The Bridge and Structural Engineer

B&SE_Volume 48_Number 4_December 2018

The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION FOR BRIDGE & STRUCTURAL ENGINEERING

Underground Transportation Structures

The Bridge & Structural Engineer Indian National Group of the International Association for Bridge and Structural Engineering

Contents :

Volume 48, Number 4 : December, 2018

Editorial l l

From the Desk of Chairman, Editorial Board: Mr. Alok Bhowmick From the Desk of Guest Editor : Dr. BC Roy

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Special Topics: Underground Transportation Structures

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Integrated Transit Corridor Development in and Around Pragati Maidan, New Delhi - A challenging Highway Project Urban Landscape Alok Bhowmick, PK Parmar Underground Transportation Tunnel: Cut and Cover Approach BC Roy, Sumit Wagh Soil-Structure Interaction Analysis of Embedded Retaining Walls for Underground Metros Makarand G. Khare, Sudheer Kumar Seekarap Palli Special Considerations of Deep Excavations and Cut-and-Cover Tunnelling in Non-Cohesive Soils with High Groundwater Level Frank Rackwitz First Tunnels Across Major River Hooghly for East West Metro in Kolkata Biswanath Dewanjee Design and Construction Aspects of Üsküdar Station in Üsküdar-Çekmeköy Metro Line (UCM) in Istanbul Emre Duman, Baris Özcan, C. Utkan Çorbacioğlu Launching the World’s Largest Tunnel Boring Machine Peter Thompson Immersed Tunnel for Bosphorus Crossing Emre Duman, Nurettin Demir, Tolga Pulak Early-Age Strength Development Monitoring of Shotcrete Tunnel Linings Current Practice Vishwajeet Ahuja Guidelines for Instrumentation and Monitoring in NATM Tunnels Ali Hayri Cuvenc, Archana Effect of Construction of UG Corridor & Stations on Influence Zone of Existing Structures BC Roy, Tanmoy Guha Assessment of Concrete Durability for Underground Transportation Structures Harshavardhan Deshpande, Madan Magdum Waterproofing - Underground Transportation Structures Rama Raju Penmatsa, Harshavardhan Deshpande Cost Optimization for Underground Metro Projects: in India Rajendra Harsh

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CONTENTS

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108 118 126

Panorma l l

Office Bearers and Managing Committee - 2018 135 Highlights of the ING-IABSE Workshop on “Inspection, Investigation and 138 Repair/Rehabilitation of Bridges & Flyovers” held at Chennai on 8th and 9th December, 2018

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Vol. 48 | Number 4 | December, 2018

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The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING

March 2019 Issue of the Journal will be a Special Issue with focus on

PREFABRICATED CONSTRUCTION FOR STRUCTURES SALIENT Topics to be covered are : • • • • •

Prefabrication – Design and Applications.

Prefabricated systems for Buildings, Industrial Structures and Housing.

Prefabrication for bridges, marine structures including foundations.

Connections in prefabricated construction.

Equipment, tools and tackles in erection of prefabricated elements.

Those interested to contribute Technical Papers on above themes shall submit the th st abstract by 15 January 2019 and full paper by 31 January 2019 in a prescribed format, at email id : ingiabse@bol.net.in, ingiabse@hotmail.com

The Bridge & Structural Engineer JOURNAL OF THE INDIAN NATIONAL GROUP OF THE INTERNATIONAL ASSOCIATION OF BRIDGE & STRUCTURAL ENGINEERING

June 2019 Issue of the Journal will be a Special Issue with focus on

STRUCTURAL ANALYSIS - RECENT ADVANCES SALIENT Topics to be covered are : • New advances in structural analysis & design software • Analysis of long span bridges, Nuclear Reactor buildings, Chimneys, Containment steel domes • Analysis for Base isolation using different type of bearings • Soil - Structure Interaction & Rail Structure Interaction • Push over analysis • Slope Stability Analysis • Analytical wind tunnel studies using CFD • Thermal analysis for solar radiation • Analysis of structure for blast loading/aircraft impact (NPCIL/AERB) Those interested to contribute Technical Papers on above themes shall submit the abstract by 1st May 2019 and full paper by 15th May 2019 in a prescribed format , at email id : ingiabse@bol.net.in . ii

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

December, 2018

B&SE: The Bridge and Structural Engineer, is a Quarterly journal published by ING-IABSE. It is one of the oldest and the foremost structural engineering Journal of its kind and repute in India. It was founded way back in 1957 and since then the journal is relentlessly disseminating latest technological progress in the spheres of structural engineering and bridging the gap between professionals and academics. Articles in this journal are written by practicing engineers as well as academia from around the world.

All material published in this B&SE journal undergoes peer review to ensure fair balance, objectivity, independence and relevance. The Contents of this journal are however contributions of individual authors and reflect their independent opinions. Neither the members of the editorial board, nor its publishers will be liable for any direct, indirect, consequential, special, exemplary, or other damages arising from any misrepresentation in the papers.

The advertisers & the advertisement in this Journal have no influence on editorial content or presentation. The posting of particular advertisement in this Journal does not imply endorsement of the product or the company selling them by ING-IABSE, the B&SE Journal or its Editors.

Front Cover: TUEN MUN-CHEK LAP KOK LINK – NORTHERN CONNECTION SUB-SEA TUNNEL SECTION As Hong Kong's deepest, longest and largest sub-sea road tunnel, this project has the largest contract sum ever awarded in Hong Kong, a reflection of the project's scale and complexity.

This dual two-lane sub-sea tunnel will run between the western New Territories and Lantau Island. The world's largest Tunnel Boring Machine (TBM) of 17.6 metres in diameter and two identical mixshield TBMs of 14 metres in diameter are used to construct the road tunnels. These state-of-the-art machineries enable real-time geological mapping of rock faces, and robotic detection of damaged components on the cutter head to reduce manual inspections under hyperbaric conditions.

Printed at: SAGAR PRINTERS & PUBLISHERS, New Delhi E-mail: sagarprinters@gmail.com

Price ` 500

Editorial Board Chair: Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt. Ltd., Noida Members: B.N. Singh, Chairman, ING-IABSE & Director General (Road Development) & Special Secretary, Ministry of Road Transport & Highways, New Delhi I.K. Pandey, Secretary, ING-IABSE & Additional Director General (Road Development), Ministry of Road Transport & Highways, New Delhi D.O. Tawade, Past Chairman, ING-IABSE & Member (Technical), NHAI Harshavardhan Subbarao, Chairman & MD, Construma Consultancy Pvt. Ltd., Mumbai V.N. Heggade, President (Engg), Gammon Engineers & Contractors Pvt. Ltd., Mumbai Umesh Rajeshirke, Managing Director, Spectrum Techno Consultants Pvt. Ltd., Mumbai Rajiv Ahuja, Consulting Engineer, Arch Consultancy Services Pvt. Ltd., Gurugram Nirmalya Bandyopadhyay, Director, STUP Consultants Pvt. Ltd., Kolkata Advisors: A.D. Narain, Former DG (RD) & Additional Secretary to the GOI A.K. Banerjee, Former Member (Tech) NHAI, New Delhi S.K. Puri, Former DG (RD) & Special Secretary to the GOI Prof Mahesh Tandon, Managing Director, Tandon Consultants Pvt. Ltd. New Delhi B.C. Roy, Advisor Transportation AECOM & Chief Executive RUPL, New Delhi Published: Quarterly: March, June, September and December Publisher: ING-IABSE C/o Secretary, Indian National Group of the IABSE IDA Building, Ground Floor (Room Nos. 11 and 12) Jamnagar House, Shahjahan Road New Delhi-110011, India Phone: 91+011+23388132 and 91+011+23386724 E-mail: ingiabse@hotmail.com, ingiabse@bol.net.in, secy.ingiabse@bol.net.in Submission of Papers: All editorial communications should be addressed to Chairman, Editorial Board of Indian National Group of the IABSE, IDA Building, Ground Floor, Jamnagar House, Shahjahan Road, New Delhi-110011.

Advertising:

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Disclaimer:

Advertising: All enquiries and correspondence in connection with advertising and the Equipments/Materials and Industry News Sections, should be addressed to Shri I.K. Pandey, Secretary, Indian National Group of the IABSE, IDA Building, Ground Floor, Jamnagar House, Shahjahan Road, New Delhi110011.

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Vol. 48 | Number 4 | December, 2018

Journal of the Indian National Group of the International Association for Bridge & Structural Engineering

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Editorial column from Chairman, Editorial Board

It is anticipated that the world population will increase from 7.7 billion to 9.3 billion by the year 2050. It is also anticipated that the population will be shifting to urban areas during this period and by 2050, the urban population will increase from 4.2 to 6.7 billion.

As per the predictions, in 2050, 70% of the world's population will be living in cities (United Nations, 2007). This is a serious challenge to all the city planners. It is quite obvious that the limited available space at earth's surface level will compel the planners to consider underground transportation corridors in the form of long tunnels. There are many such corridors already coming up in cities for metro as well as for highways. Coming years will therefore see a greater use of underground transportation structures.

There are several stated advantages of building underground transportation structures in terms of mobility, quality of life and economic and social sustainability. The decision on whether to place an urban transport infrastructure underground or aboveground is however quite complex due to high initial cost of UG

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structures. Planning, engineering, construction, urban design, economic and political aspects are therefore to be factored in while taking a decision. For the choice to be made well, both short and long term costs and short and long term benefits need to be objectively and comparatively considered.

In short, the driving factors for encouraging underground construction is the growing awareness on quality and sustainability, growing pressure on available (urban) space, growing urbanisation, large economic growth/ prosperity, technological progress, active government / political pressure.

Sustainable future has to take into consideration also the need to disseminate the knowledge of civil and structural engineering around us on current issues of importance, which has societal impact. Considering the rapid growth in the construction of underground transportation structures around us in the recent past and also the future prospects of its widespread applicability, the editorial board thought it prudent to dedicate

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this issue of the journal to “Underground Transportation Structures�. The main objective is to present an overview of the latest scientific advancements and the state of practice in the area of underground transportation structures.

There are in all 14 papers on the theme covering planning, design, construction, structural assessment, maintenance and monitoring.

For this special issue, we are privileged to have Dr B C Roy as our Guest Editor. He is an eminent personality in the field, a specialist for underground transport structures and well known in IABSE circles for his immense contribution in the field of Civil Engineering.

I hope readers will find this issue informative, thought provoking, insightful and interesting !

Happy Reading !

(ALOK BHOWMICK)

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

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From the Desk of Guest Editor

The transportation crisis in urban Indian cities is deepening with lack of space on ground to further develop transportation facilities. Higher degree of congestion, noise pollution, increased motor vehicles; unplanned suburban sprawl, uncoordinated land use and transit planning are making the matters worse. The planners and developers are either going elevated or underground for appropriate solutions.

Construction industry, one of the world's biggest employers, plays a large part in a country's economy by building the necessary infrastructure. Infrastructures generate construction jobs and boost economies. A planned and coordinated approach to urban transit planning requires innovative thinking both meaningfully, and safely. It is equally critical to integrate land use vision with the needs of travelers, developers, public and the environment. Providing sustainable urban transit solutions is a major requirement today and underground structures have developed a long way to address the issues Nowadays underground structures for infrastructures are becoming very important particularly in Indian context where the cities are thickly built-up with narrow lanes. Innovative use of underground for commercial and residential use, storage, water conveyance and treatment, and heritage conservation brings in more optimal solutions for urban development. It is the main driving force in underground space engineering for both developing and developed

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countries. Safe innovation-safety of structure, users and workers, taken integrally-is an overriding issue. As structural engineers we need to look at the magnitude of these incidents, not necessarily to fix the liability but also, to make them nonrepeatable. We must innovate with due diligence including risk management.

Most of the Indian Cities are historical cities with lack of space in the green field areas.

Building infrastructure on ground or even elevated is difficult. Going underground is the best option even though the cost increases.

An attempt has been made in this issue to address the hindrances related to infrastructures particularly underground structures for a better built environment. The deeper under the ground we go the costlier it becomes. As such the papers are aimed at innovations and best space utilization corresponds to existing condition of built-environment, building condition, geotechnical and soil structure interactions, amongst others. This edition is aimed at providing readers on the ongoing developments intermingling the past with present and future technology.

We are indebted to the eminent contributors, for their time in developing their papers, without whose support bringing out this issue would not have been possible. The shortlisted papers gave emphasis on innovations, case studies, mostly relating to transportation infrastructure particularly underground structures. Due to

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space constraints and late interaction, we could not include few international papers. The papers, included could be broadly classified under underground structures overview, types and technique, geotechnical, case study, design and construction, tunneling, existing buildings condition, instrumentation, durability, waterproofing and cost.

The selected papers include a paper on the planning and design aspects of underground transport infrastructure development followed by a few papers on the underground tunnel and station techniques like Cut and Cover approach.

The approach was adopted in the first metro construction in India in the seventies. Even though it was based on empirical approach developed through experience gained for building of underground structures in different countries, globally, the technology has come up a long way and today's metro construction particularly stations and tunnel designed through IT help and different software. Now the technologists are comfortable to plan for deeper underground design and construct metros using NATM and TBM techniques. Earlier days segments used in tunnel construction was made of cast iron. First precast concrete segments used for tunnel construction was in Germany and in the year 1974. Technique used for the underground lining in the first Indian metro was a combination of precast concrete &cast iron that has paved the way for concrete precast lining adopted today. A paper discusses the current practice in lining.

Paper on soil-structure interaction gives an insight into the new technology. Also a paper on special considerations of deep excavations and cut-and-cover tunneling gives more information. Couple of papers presents the case study of metro tunneling and stations in India and abroad. A paper is also included presenting information on the launching technique of the World's Largest Tunnel Boring Machine.

A paper is also included on immersed tunnel.

This concept was mooted in the 1990.s in India but there were a lot of apprehension at that time.

Subsequently now the Indian technocrats are

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trying to make it a reality in Mumbai. Ing-IABSE is planning a Seminar/Workshop on the Immersed Tunnel soon to discuss more on the theme We had talked about the NATM earlier. In this regard the instrumentation and its monitoring is very important. A paper discusses this aspect in more details.

Since most of the Indian cities are historical and passes through congested corridors the building condition survey assumes great importance. A paper precisely discusses the aspect. Couple of papers discusses the Assessment of Concrete Durability and Waterproofing in Underground Transportation Structures.

In planning, designing, construction and maintenance of Underground Metro Projects in India, financial viability is one of the most important aspects. Paper on Cost Optimization discusses how a metro, a non-viable project could be made viable. Even though no values or case study is given, paper covers the general issues following the concepts, which will help the decision makers in saving time and cost. The first metro was built by Indian Engineers with very little help from expatriates. Present and future Metro Projects particularly, underground could do away with expatriates whose cost and stay is very costly, saving cost and foreign exchange.

The members of the Editorial Board are providing the technocrats particularly the Indian Engineers to present their thoughts through these knowledge based papers and no words of appreciation would be enough for them. I am personally thankful to all and each one of them for their guidance and support.

I convey my best regards to each of the contributors who are themselves eminent personalities in their field. I believe the readers will find the edition interesting and will be happy to read this issue and make it a prized possession.

(B.C. Roy)

Vol. 48 | Number 4 | December, 2018

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Brief Profile of Dr. BC Roy Dr Bidhan Chandra Roy's engineering activities espouse multiple facets – technology, innovations, research, management and business growth. The projects he has carried out carry hoi signature of innovative features, leveraging across projects, that are meaningful in the context of reduced imposition on resources, speed of construction and which also accord priority to environmental concerns.

Dr. Roy's contributed arcos the gamut – conceptualizing and planning, investigations and design, value engineering, construction, project management, research and teaching. He has mentored many a young talent. He has gained high level expertise and effectively leveraged it in structures for mass housing, bungalows & high-rise buildings, Mass Rapid Transit Systems, large span roofs including shell roofs, underground structures including metros, bridges, grade separators, industrial structures, sports structures, earthquake affected structures and innovative designs for fast track construction.

Acknowledging his professional accomplishments, he has been conferred fellowship of a number of learned and professional academies and institutions, including the Indian National Academy of Engineering, the Institution of Civil Engineers, UK, Institution of Structural Engineers, UK the Institution of Engineers India, and International Association of Bridge & Structural Engineering, Zurich. He is Vice President of IABSE, Zurich, the third Indian in the 84 years history of the Association and is the Chairman of the Scientific Committee of the IABSE International Conference on “Long Span Bridges and Long Span Roofs - Development, Design and Implementation” to be held in Kolkata in September 2013, which is drawing professionals from more than 30 countries, fro across the world.

While even a short list of the iconic projects – incorporating innovations that turned out to be essential – he has been involved in will necessarily be long, mention must be made of a few: Ø Designed strutted diaphragm wall with semiintegrated and integrated with boxstructures, for the first time in India for a stretch of the Kolkata Metro; Ø Joint Project Director, of the General C o n s u l t a n t t o K o l k a t a M e t ro R a i l Corporation Limited in the prestigious EastWest Metro Project in Kolkata; Ø Prestressed voided slabs, first time in India for the Howrah Approach of the Second Hooghly Bridge;

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Ø Pioneered contiguous prefabricated I-girder system for flyover superstructure accommodating various curvatures or a series of flyovers in Delhi and Mumbai. Planned and designed the centralized precasting factory; Ø Developed precast segmental arch pedestrian subway in Delhi and Mumbai Ø Developed a framing system using precast concrete units extensively to cover the drain and convert the area so released as roadway, also improving the environment Ø Pioneered top-down construction for urban transport structures in India – for four level (first time) Punjabi Bagh intersection along Ring Road, New Delhi and taken it beyond to other parts of India Ø Reintroduced Steel-concrete composite systems for flyovers in Delhi Ø Introduced extradosed concept for the Second Viveknanada Bridge across River Hooghly in Kolkata. The bridge was adjudged the most innovative international design by the American Segmental Bridge Institute (ASBI) Ø Planning, design and implementation of a workshop building with long-span high-level roof employing semi-continuous hyperbolic paraboloid shell with 21m-grid dimension for the central excavation workshop at Gevra Ø For 3,600 housing units in an earthquake reconstruction effort under tight time schedules in Marmara, Turkey, he ensured robust design and timely and cost-effective execution Ø Developed the first Concession Agreement for BOT Project at Mumbai Trans Harbour Link and continued it for Second Vivekananda Bridge, Kolkata Ø Project Director for a number of Stadiums for Commonwealth Games 2010. Ø Team Leader for developing the Master Plan for Nairobi Mass Rapid Transport System for the first metro project in East Africa.

Dr. Roy made a name for himself in research for his work on silo structures. Dr. Roy got his PhD in Engineering for this research, carried out in Australia. He was one of the 12 invited authors world-wide for a chapter in the book Worldwide Wall Enclosures (CIB Commission W023-Wall Structures) and he focused on masonry structures. As a Distinguished Visiting Professor under the aegis of AICTE-INAE he has delivered lectures at IIT Powai, Mumbai & Jadavpur University, Kolkata.

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INTEGRATED TRANSIT CORRIDOR DEVELOPMENT IN AND AROUND PRAGATI MAIDAN, NEW DELHI – A CHALLENGING HIGHWAY PROJECT URBAN LANDSCAPE

Alok BHOWMICK

P K PARMAR

Managing Director, B&S Engineering Consultants Pvt. Ltd.

Chief Project Manager (Flyover), Public Works Department, GNCTD

Mr. Alok Bhowmick, graduated in Civil Engineering from Delhi University in 1981 and did his post-graduation from IIT, Delhi in 1992. Mr Bhowmick He is an active member of several technical committees of IRC and BIS. He is a fellow member of governing council of Indian Association of Structural Engineers & Consulting Engineering Association of India. He is Vice Chairman, ING-IABSE and also chairman of Editorial board of the Journal “The Bridge & Structural Engineer” published by ING-IABSE.

Summary The integrated transit corridor project, is a part of the mega project of GoI for redevelopment of India Trade Promotion Organisation (ITPO) complex into International Exhibition cum Convention Centre (IECC) at Pragati Maidan. The project is presently under construction on fast track mode and is likely to be completed by August 2019. The integrated transit corridor development project is a part of this mega project and comprises of construction of the following major structural components: –

A divided 6 lane highway tunnel of about 1.1 Km long, passing through the Pragati Maidan.

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Mr P.K Parmar, graduated in Civil Engineering from M.B.M Engineering College Jodhpur in 1986 and did his post- graduation in 2012 from the same college. The highlights of his career spanning more than 32 years includes planning, design and execution of buildings, industrial structures, Border fencing on Indo- Pak Border and mega infrastructure of Delhi. He was also involved in the prestigious project of Barapullah Nallah Elevated Corridor (Phase-II) from Jawahar Lal Nehru Stadium to INA. Currently he is in charge of two mega projects in Delhi (i.e.

Barapullah Nallah Elevated Corridor Phase III from Sarai Kale Khan to Mayur Vihar involving a bridge of extradosed type over river Yamuna and the most challenging Pragati Maidan Integrated Corridor project, which is the subject matter of this paper). Mr Parmar was also actively involved in planning of various corridors in Delhi which include Kalindi Kunj Bypass project from DND Flyover to Badarpur Border, elevated road at Mangal Pandey Marg & also planned Flyover at Shastri Park & Seelampur in Delhi.

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3 Nos. of 2 lane U-turn Underpasses (No. 1, 2 & 4) along Mathura Road between Pragati Maidan Station and DPS.

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1 No. of 3 lane underpass (No. 3) near Purana Quila Road.

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3+2 lanes Underpass no. 5 near Bhairon Marg & Ring Road T-Junction.

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2 lane Underpass no. 6 at Bhairon Marg.

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Widening & Strengthening of existing roads around Pragati Maidan & allied works.

This is a rare project with several unique features, requiring creative and innovative solutions. This Vol. 48 | Number 4 | December, 2018

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amenities and basement having parking facility for 180 cars.

technical paper highlights some of the salient features of the project.

1.

Introduction

The Pragati Maidan Exhibition complex has been an icon for the city, which was inaugurated in 1972 and since then, it has played host to an innumerable number of exhibitions and conventions, besides the world famous India International Trade Fair (IITF) held every year in November.

Over the years, the need for expansion of the facility and its modernisation has been felt due to various compelling reasons (i.e.. Inability to host international level large exhibitions; Low exhibition area density; 33% of existing exhibition space non-usable during most of the year; Over-utilisation in peak season; Presence of few regular, large events lead to capacity short fall; Declining market share etc.). Accordingly the Government of India (GoI), Ministry of Commerce (MoC) has decided to redevelop the facility into a global level iconic, self-contained, totally integrated, state-of-the-art infrastructure for organizing international exhibitions, business events, meetings, and conventions. The various components along-with its objectives are given as under : a)

State of the art Convention Centre with combined capacity of 13,500 people, which is many a times the capacity of Vigyan Bhavan

b)

Exhibition Halls: There are a total of 11 exhibition halls proposed in the main redevelopment strategy.

c)

Basement: Designed over total built-up area of 1,68,305 sq. mtrs. Which is divided in two parts – Administration Basement and General Basement, meant for parking facilities of 4800 ECS, which will be connected to the Ring Road through a series of tunnels, thereby freeing traffic on Mathura Road.

d)

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Administrative Block: The Administration Building is designed over a total Area of approx. 8857 Sqm. With all modern

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e)

3.7 acres land for a star hotel – Future provision

f)

Ticketing Plaza and Gate Houses with large LED digital walls

g)

Food & Beverage Kiosks

h)

Skywalk from Pragati Maidan Metro Station

i)

Covered Walkways

j)

Extensive landscaping and water bodies

k)

Musical Fountains

l)

Amphitheatres – which will seat 3,000 people, is touted to be one of the largest single-gathering space.

m)

Integrated infrastructure development to decongest traffic in and around Pragati Maidan Complex (i.e. Mathura Road, Purana Quila Road and Ring Road connectivity)

The project is planned to be executed in two phases.

The Phase-1 redevelopment is expected to cover approximately 3,82,188 m2 of built-up area, which will cover Convention Centre, Administrative Block, 6 nos. of Exhibition Halls, Basements including the integrated transit corridor connecting Mathura Road with Ring Road. Phase-I is scheduled to be completed by May 2019. Phase–II will cover balance 1,96,000 m2 of builtup area comprising of remaining exhibition halls (5 Nos.). The total cost of the Pragati Maidan redevelopment project is estimated to be Rs 2,600 crore for Phase-1. Fig. 1 shows the layout plan of the integrated Exhibition cum Convention Centre (IECC).

This article will focus only on the proposed integrated infrastructure development planned in and around Pragati Maidan to decongest the traffic around Mathura Road, Purana Qila Road & Ring Road (i.e.

Item m) above). India Trade Promotion Organisation (ITPO) decided to take up the decongesting work of the area around Pragati Maidan on priority, even before

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the exhibition grounds could be redeveloped. This work involves construction of 6 lane wide, 1.1 Km long tunnel from Purana Qila road to Ring Road running below Pragati Maidan. This tunnel will also give access to the parking lot inside Pragati Maidan. Apart from this main highway tunnel, 6 road underpasses are also proposed in Mathura Road, in the vicinity of Pragati Maidan. The infrastructure development thus planned is expected to take the huge traffic related pressure off the ITO & Bhairon Marg intersections and make the surrounding area signal free. A large portion of East bound traffic will use this tunnel for a quick getaway. With Mathura road also becoming signal free, traffic situation will improve leaps and bounds in the surrounding area.

Connaught Place may enter this tunnel through the same branch by making a U-turn via Underpass-4.

The tunnel runs below the Pragati Maidan area & culminates at Ring Road and has 4 connecting branch tunnels ramps/loops which takes care of traffic in all directions of the Ring Road. This tunnel also has a 100m long box pushing section under 7 railway tracks just beyond the Pragati Maidan Boundary towards Ring Road. The tunnel will also provide access to the new parking lots of Pragati Maidan’s International Exhibition cum Convention Center (IECC) from branch tunnels connected to it. Apart from this, passenger cars can also commute from one side of the basement to the other from underneath the tunnel through 2 cross tunnels which are integrated with the main tunnel.

Table 1 : Percentage break-up of Project Cost (Approx) Sl. Particulars No.

Approximate % of Cost

1.

Man Tunnel; with 6 Lane divided carriageway

40%

2.

Connecting Branch Tunnels from Main Tunnels to Underground parking of basement of Pragati Maidan

10%

Fig. 1 : Layout Plan of IECC, Pragati Maidan

3.

Underpasses (6 Nos.)

36%

The project is being funded entirely by the central government. Delhi government’s Public Works Department is entrusted with this part of the project and the contract was awarded to Larsen & Toubro Limited (L&T) on EPC mode at a cost of Rs. 777.00 Crores. The work commenced in November 2017 and is planned to be completed in August 2019 (construction time allotted : 660 days). The percentage break-up of the cost (Approx.) in various components are given in Table 1 below.

4.

MEP (including Fire Fighting)

8%

5.

Miscellaneous (Consultancy services, TPQA, Improvement of adjoining Roads & maintenance during project period, Art Work, FOB, Shifting of Storm water Drain, Handing over of Site and Construction of offices

6%

2.

Salient Technical Features of the Proposed Integrated Transit Corridor

The 1.1 km main tunnel has a divided 6 lane configuration. Main entry to this tunnel is through the Purana Qila road towards Pragati Maidan. Vehicles travelling on Mathura Road towards Nizamuddin can enter this tunnel through its branch tunnel whereas, vehicles on Mathura Road going towards The Bridge and Structural Engineer

TOTAL

100%

Apart from this 6 lane main tunnel, 4 Underpasses are proposed at various locations on Mathura Road over 3 Km stretch between Pragati Maidan metro station and Delhi Public School. 2 Underpasses are also proposed at Bhairon Marg providing connectivity to underground parking inside Pragati Maidan. In addition there are 2 sets of Underpasses proposed Vol. 48 | Number 4 | December, 2018

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connecting Ring Road and Bhairon Marg. Details of these underpasses are as under: a)

2 lane U-turn Underpass no. 1 near DPS, Mathura Road.

b)

2 lane U-turn Underpass no. 2 near Kaka Nagar.

c)

3 lane U-turn Underpass no. 3 near Purana Quila Road & Mathura road T Junction. This underpass also provides direct connectivity to Bhairon Marg.

d)

2 lane U-turn Underpass no. 4 near Bhagwan Das road to Mathura Road T Junction. This underpass also includes branch tunnel to Pragati Maidan underground parking, branch tunnel from Gate no. 8 of pragati maidan to parking of admin block near the new Supreme Court Building & facilitates a U-turn on Mathura road for entry in to the main tunnel.

e)

3+2 lanes Underpass no. 5 near Bhairon Marg & Ring Road T-Junction, making it signal free.

f)

2 lane Underpass no. 6 at Bhairon Marg which provides connectivity to Pragati Maidan underground parking.

Widening & reconstruction of a portion of Mathura Road, Purana Qila Road & Bhairon Marg is also being done under this project. Improvement of the following existing intersections is also being taken up which are deficient with respect to the prevailing IRC standards: a)

Bhairon Marg & Mathura road T-Junction

b)

Purana Qila Road & Mathura road T-Junction

c)

Bhagwan Das Road & Mathura road T-Junction

d)

Bhairon Marg & Ring Road T-junction

e)

Sher Shah Road & Mathura Road T-junction

f)

Subramanium Bharti Road & Mathura Road T-Junction

Fig. 2 shows the layout plan of the various infrastructures planned around the Pragati Maidan for decongestion.

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Fig. 2 : Layout Plan of Infrastructure for decongestion of Pragati Maidan area

3.

Salient Design Features of the Project

3.1 Highway & Drainage Design Philosophy Highway Geometrics Geometric design of the highway for all Underpasses, Tunnels, Ramps, existing roads are designed in accordance with Schedule B provisions of the contract and the relevant IRC standards and MoRT&H specifications. Following geometric design parameters have been followed in this project : y

Design Speed

: 80 Km/Hr for the Main Tunnel : 40/30 Km/hr. for the ramps of Underpass and Tunnel portion

y

Curve Radius

: Varies from 50m to 300m for Main Tunnel+Ramps : 50m to 112m for Branch Tunnels : 36.5m to 500m Underpasses

y

in

Vertical Gradient : Varies from 0% to 3.3% for Main Tunnel+Ramps : Varies from 0% to 4.0% for Branch Tunnels : Varies from 0% to 3.84% in Underpasses The Bridge and Structural Engineer

y

Super elevation

: Provided as per provision of IRC:86-1983

y

Vertical Clearance

: Main Tunnel – 5m, Underpasses 1, 2 & 5 – 5.5m; Underpasses 3,4 & 6 – 5.0m

Drainage System Surface drainage on roads are provided each side in conformity with the provisions of IRC:SP:50-2013. For the super-elevated portion of roads, median drains are also provided. For tunnel / underpasses, a drainage system is installed to divert surface run-off. The surface run-off from each ramp and open to sky portions is collected in the sumps through longitudinal drains, provided on the sides. Sumps are designed for 5 minutes retention of run-off. The collected run-off in sumps are proposed to be lifted through submersible pumps and discharged to the nearest surface level drain or manhole. 2 submersible pumps are provided in each sump. Design of pump capacity is based on the assumption that only one pump will be operational at a time.

Pavement Design Philosophy Flexible pavement is proposed for areas / location where road widening, road strengthening, reconstruction is to be done in the surrounding area around Pragati Maidan. Concrete pavement proposed in ramps and covered tunnel portion. Flexible pavements are designed for a minimum design period of 15 years. Design life of concrete pavement is 30 years. The minimum design traffic considered for pavement is 50 Million Standards Axle (MSA) for main road, 30 MSA for slip roads and 10 MSA for service roads.

3.2 Structural Scheme & Design Philosophy for the Main Tunnel, Underpasses and Ramps Salient Structural Scheme The covered portion of 3+3 lane main tunnel is a 2 cell RCC box structure which is being constructed cast-in-situ, using cut and cover method, except below the railway portion, just beyond the pragati maidan boundary, where box pushing technique is used. The The Bridge and Structural Engineer

ramps/loops at entry/exit of the tunnel consists of RCC U-TROUGH structure. The tunnel is provided with a clear height of 5m & its width varies from 28m to 38m. The entire carriageway is divided for traffic partly by intermediate wall & partly by RCC columns.

The thickness of walls varies from 0.8m to 1.2m.

Wherever columns are provided, they have a typical square dimension of 1.00x1.00 m with a spacing of 5.75m along the length of the tunnel.

The buried tunnel portion inside Pragati Maidan area has landscaping on top of it. The filled up soil thickness over it varies from 0.3m to 1m. However, it has been designed for a minimum thickness of 1m as per the provisions of the contract. Although there is no provision for vehicular movement over the tunnel, except at Mathura road, the tunnel is designed for a static live load of 4 t/m 2 , to cater for possible movement of fire tenders over it in case of emergency.

A portion of main tunnel lies directly beneath the exhibition Hall A-6 of IECC project, which makes the structural scheme very complex and challenging, since the structure is split into two separate units with two different agencies involved in design as well as construction. Columns of this hall directly rests over the top slab of the tunnel. Therefore, in order to design this portion of the tunnel, pre-stressing has also been introduced along with pile foundation to transfer load to the soil. Beyond the Pragati Maidan boundary, vehicular loading as per IRC:6 has been considered.

A 100m stretch of the tunnel just beyond the Pragati Maidan boundary passes below 7 railway tracks of the Northern railways from New Delhi to Mumbai.

Construction of this length is being carried using box pushing technique and is being looked after by the Indian Railways.

Apart from the main tunnel, 6 underpasses are also being built in the surrounding areas which have similar structural configuration as the main tunnel. The highway geometrics of all tunnels are based on the provisions of IRC:86. The structural modelling & analysis has been done using softwares like STAAD Pro and LUSAS. Structural design has been done as per the provisions of IRC:112. Fig. 3 to Fig. 6 shows the dimensional details of the various components of Main tunnel and Underpasses.

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5

Design Philosophy The design service life for all structural components (RCC Box structures as well as U-troughs) is considered as 100 years. Salient features of the structural design are as follows: Fig. 3 : Typical Cross Section of 6 Lane Main Tunnel (Closed Box Portion)

y

Minimum Grade of : M45 for RCC; M20 for Concrete Levelling Courses.

y

Min. Grade of Reinft

: Fe 500D. The reinforcement shall be corrosion resistant steel (CRS).

y

Exposure climatic condition

: “Severe” for outer faces in contact with earth and “Moderate” for inner faces.

y

Cover to Reinforcement

: 75mm for foundation and outer face of RCC Box / U-trough; 45mm for inner faces.

y

Design Ground Water Level

: For the stretch of the Main tunnel from Mathura Road to Railway Boundary, the GWT is considered as 204.55m. For all other locations, it is considered as RL 206.30 or the existing ground level, whichever is lower.

y

Vehicular Live Load : For the underpass, live load shall be considered as per IRC:6. For the roof of underpass.

Fig. 4 : Typical Cross Section of Underpass (Closed Box Portion)

Fig. 5 : Typical Cross Section of 6 Lane Main Tunnel (Open to Sky Portion)

3.3 Waterproofing System

Fig. 6 : Typical Cross Section of Underpass (Open to Sky Portion) 6

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Stringent waterproofing system is proposed for this structure. This includes providing and mixing of integral crystalline admixture for waterproofing treatment to RCC structures, which is mixed at the time of transporting of concrete. The crystalline admixture shall be capable of self-healing of cracks upto a width of 0.5mm. The material used as

The Bridge and Structural Engineer

crystalline admixture shall conform to ACI-212-3R2010, with minimum dosage of 0.8% to the weight of cement per cubic metre of concrete and shall reduce the permeability of concrete by more than 90% compared with controlled concrete as per DIN 1048.

In addition to the above, following waterproofing system is proposed to be used for raft, retaining wall, basement roof and water stop at construction joints : a)

For Base Raft / Base Slab

Pre-applied water proofing membrane should be having a minimum thickness of 1.2mm. Fully bonded membrane shall comprise of HDPE layer of not less than 0.8mm strong adhesive and protective layer with following properties : y

Minimum elongation at break of 400%

y

Peel Strength of concrete > 800 N/m

y

Puncture resistance > 900 N

b)

For Retaining Walls

Cold applied, flexible self-adhesive polymer modified asphalt waterproofing membrane with laminated HDPE film. Membrane should be of minimum thickness of 1.5mm with HDPE layer of minimum 0.2mm. The membrane should have the following properties : y

Minimum elongation at break of 200%

y

Puncture resistance > 250 N

y

Lap Adhesion of 650 N/m

c)

For top slab of tunnel / Underpass

3.4

Geotechnical Aspects

The geotechnical investigations was carried out at site in and around November 2017. The investigation indicates that the sub-soil is primarily a mixture of various layers of Non plastic sandy silt / Silty Sand / Fine Sand / Clayey Silt / Sandy Clay / Silty Clay of low or medium plasticity. Ground Water table is observed at a depth of 2.30m to 7.5m below the existing ground level at the time of investigation.

Liquefaction potential of the sub-soil is also assessed.

For the purpose of liquefaction potential assessment, the peak ground acceleration values are taken from the published microzonation maps for NCT Delhi prepared by National centre for Seismology, Ministry of Earth Science, Govt. of India. The sub-soil is found to be in loose condition and is prone to liquefaction upto 6 to 7.5m below the existing ground surface at some locations near the main tunnel portion. Wherever, the founding level of the structure lies above potentially liquefiable soil, ground improvement & soil replacement is being carried out.

The RCC Box structures or the RCC U-trough structures are proposed to be constructed in-situ by cut and cover method in a bottom-up sequence. A net safe bearing capacity of 10t/m2 is considered for design purpose as per recommendations by the Geotechnical Expert. This SBC is derived based on an assumed allowable settlement of 75mm for the foundation. Photo 1 to 6 shows various stages of construction of the main tunnel.

Single component, environment friendly, water based, non-toxic, with low VOC, polyurethane membrane in minimum 1mm thickness, with following minimum properties has been used : y

Minimum Tensile Strength : 1.9 Mpa

y

Minimum elongation at break of 450%

y

Minimum Tear strength of 12 N/mm

y

Solid content of minimum 90% Photo 1

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7

Photo 6 Photo 2

4.

Mechanical, Electrical & PHE Services (MEP)

It is necessary to make provision of ventilation and lighting all through the tunnel.

4.1 Tunnel Lighting System

Photo 3

Tunnel lighting criteria conforms to CIE guidance (CIE 88). The lighting system is specially designed such that there is more lighting at the entry and gradually reducing inside the tunnel with an increase at the exit point.

For planning the lighting of tunnel, the tunnel length is divided into four zones. They are : a) Threshold zone, b) Transition zone, c) Interior zone and d) Exit zone.

Table 2 gives the Lighting Level to be achieved in the Tunnel.

Integrated Tunnel Control System

Photo 4

Photo 5 8

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An integrated tunnel control system will be installed in the project that will remotely monitor one or more tunnel controls. The tunnel lighting falling in the Threshold and Transition zones are to be controlled by the Tunnel Control Unit placed inside the feeder pillars with the help of Photometer through SCADA Tunnel Management System for remote monitoring.

There are provisions for emergency override switch, a digital input that forces the full tunnel lighting to the maximum light level in case of emergency situations, such as accidents. The emergency switch shall be manually operated at each Feeder Pillar and can also be operated remotely from the Tunnel Control Room workstation.

The Bridge and Structural Engineer

Table 2 : Lighting levels to be achieved at site Zone

Length of Zone

Day/ Night

Average Luminance (In cd/m2)

Uniformity (U 0)

Longitudinal Fittings to Uniformity be used (U f )

Threshold- 1

0m-50m

Day

150.0

40%

60%

Threshold- 2

51m-100m

Day

150.0 to 60.0

40%

60%

Transition

101m-170m

Day

60.0 to 8.0

40%

60%

Interior

171m from entry upto 60m before exit

Day

8.0

40%

60%

Exit

Upto 60m before exit till exit

Day

40.0

40%

60%

Night Time

0-1.2 Km approx.

Night (Upto exit)

Night

4.0

40%

60%

IP65, IK-08 LED fittings or better

—do—

Failure monitors will also be installed, which shall monitor the failure of a group of luminaires (at least 3 luminaires) so as to detect any change depending upon the decrease in the current rating. The status of the failed luminaires will be communicated to the Tunnel Control room through Fibre Optic Cable.

3.

Incident Operation – Traffic is slow moving or stopped due to accidents or breakdown in or beyond the tunnel.

4.

Emergency Operation – These are operations that require the intervention of emergency services.

4.2 Tunnel Ventilation System

Design Criteria

The ventilation system for the tunnel comprises unidirectional jet fans with silencers. Though the jet fans are unidirectional, these operate in the reverse direction also in case of emergencies. The motors are provided with moisture oil and fungus resisting insulation of a type specifically designed and constructed to withstand severe humid condition and to operate after a long period of idleness without drying out.

The basic principle of tunnel ventilation is dilution of vehicle emissions by providing fresh air and then removing the exhaust air from the tunnel. The exhaust air can be removed via a portal (a location where the tunnel carriageway opens up to the surrounding environment), via a ventilation outlet (such as a stack), or via a combination of both. This objective can be achieved by the following:

The tunnel ventilation is required to ensure that the tunnel will operate with low risk and with acceptable air quality at all times. The operating conditions can be divided into the following categories.

1.

Preventing the dangerous accumulation of vehicle-emitted pollutants (i.e., carbon monoxide CO, and oxides of nitrogen, NOx)

2.

Maintaining visibility in the tunnel by preventing the accumulation of haze-producing pollutants.

1.

Normal Operation – Traffic is freely flowing.

System Design

2.

Congested Operation – Traffic is slow moving due to vehicle build up.

Simulation analysis including 1-dimensinal and 3dimensional (CFD) analysis has been performed for

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Vol. 48 | Number 4 | December, 2018

9

the ventilation design of tunnel. Numbers of cases were performed and only Longitudinal ventilation system with Jet Fans is found possible. The main tunnel shall be equipped with 28 jet fans (16 jet fans of type1, 804 mm dia and 12 jet fans of type-2, 630 mm dia). The branch tunnels connecting basements shall be equipped with 8 jet fans of type- 1 (2 fans in each connecting branch). This leads to a total of 36 jet fans in tunnel.

e)

Fire water static Storage (above ground) : Fire water static storage (above ground) has been provided in accordance to NFPA.

f)

Fire Pumping System: Pumping system comprising of independent pumps for hydrant sprinkler & jockey application has been provided.

g)

Hydrant system: Hydrants complete with hose reel.

5.

Protection

h)

Sprinkler System: Sprinkler rating and type shall be selected for respective areas.

It is necessary to make a provision of fire-fighting system for the connecting branch tunnels, cross tunnels and the main tunnel of the proposed development, for taking care of any fire hazards and even for washing and cleaning of the tunnels etc. The basic requirement is made compliant to NFPA 502, NBC 2016 (Part 4) of BIS, IRC-91 and Local Fire Authority Norms. In addition, other codes which are also used in designing the fire-fighting system are NFPA 10, NFPA 13, NFPA 14, NFPA 502, NFPA 20, IRC-SP:91, IS-15105, IS-2190 - 2010, IS: 15301. The Minimum fire protection and fire life safety requirement is based on tunnel length and the same is differentiated into various categories. As per IRC-91 the tunnel comes under medium category as the length of the tunnel lies between 500m to 1500 m. As, per NFPA-502 when the tunnel length equals or exceeds 1000 m (3280 ft.), it comes under “Category D” and when the tunnel length equals or exceeds 300m (800ft), it comes under “Category C”. In this case, the main tunnel length equals 1120m, thus the requirements of tunnel conforming to “Category D” as per NFPA-502has been considered. As per Indian Standards the tunnel has been classified under Moderate Category and thus the design principals with respect to Moderate category has also been adopted.

i)

Hand held fire extinguishers: Strategically placed at designated areas as per NFPA-502 and IS Standards. The installation is also to have consent of Local Fire Service Authorities.

Fire Fighting System

&

Fire

Following functional systems are provided, in compliance with the listed reference standards: d)

10

Piping System: Piping system confirming to IS: 1239, ASTM A53B – MS Heavy Class.

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The entire fire safety installation is made compliant to ensure the highest safety standard and uniformity of system. Further, the fire protection system is planned to be fully tested under simulated conditions before the tunnel is opened to traffic. Fig. 7 shows typical details of ventilation, electrical and fire-fighting fixtures in the tunnel.

Fig. 7 : Typical Cross Section of Underpass (showing MEP fixtures)

Conclusions Execution of such complex mega projects on a fast track requires a good team work between all the stake holders. The design of structural components for this project focussed on adoption of innovative engineering solution using local material and available equipment’s with the contractor. It is expected that the project will be completed within the stipulated period. Once operational, this project will not only bring considerable relief to the commuters in Delhi, but also bring down the pollution level in the area by reducing the idle time of vehicles on signals.

The Bridge and Structural Engineer

Credits y

Owner Client

y

Proof Consultant : B&S Engineering Consultants Pvt. Ltd.

: Public Works Department, GNCTD

y

Contractor (EPC) : Larsen & Tubro Limited

y

Design Consultant : Ramboll India Pvt. Ltd.

Quantities of Major Items (Approx.): y

Concrete

y

Reinforcement

: 21,250 MT

y

Waterproofing

: 2,80,000 sq.m

y

Crystalline Admixture : 830 MT

References 1.

Video by Ministry of Commerce & Industry : https://www.youtube.com/ watch?v=YNn4pvCgVHI

: 2,50,000 cu.m

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UNDERGROUND TRANSPORTATION TUNNEL: CUT AND COVER APPROACH

Dr. B C ROY

Sumit WAGH

BCE, M.Tech (Struct), Ph.D MD, RUPL

BE, M.Tech Structural Engineer AECOM

B C Roy, FNAE, Ph.D, M.Tech (Struct.), BCE. In a career spanning over 45 years in Civil/Structural engineering, Dr. Roy has dealt with many multi-disciplinary projects; experience ranging from developing concept plan to execution and has adopted innovative techniques in his designs. He was Chief Engineer for part of Kolkata NS Metro, FIRST Indian Metro and PD/JPD for EW Metro passing under River Hooghly. He is a Fellow/Member of many professional associations of repute.

Sumit Wagh, got his Master ’s Degree in structural Engineering & Bachelor’s degree in Civil Engineering from Yeshwantrao Chavan College of Engineering, Nagpur. He has experience in underground metro, Tunnel, residential buildings, Oil and Gas industry.

Abstract Kolkata Metro Railway, the first ever metro in India, was designed and constructed, using Cut & Cover technique. The Metro was planned, designed and constructed by Indian engineers and contractors except a small part using shield tunnelling. The construction work of first Metro started in 1973 and the first section was opened to passenger traffic in October, 1984. Subsequently the experience gained in Kolkata Metro was very useful for design and construction of metros in other cities.

India is rapidly growing country in terms of economy, population, infrastructure etc. The Country has undertaken several transportation infrastructure projects including rail-based mass transits, at grade, elevated and underground metro.

Numbers of Metros are already in operation, few are in development stage and some are in planning.

This paper gives emphasis on design and construction techniques and advancement in Engineering and Technology in Indian metro structure since 1970.

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Vol. 48 | Number 4 | December, 2018

Key Words: N-S (North-South) Kolkata, EW (East West) Metro Kolkata, Greenfield, Semi Integrated and Integrated Introduction Indian underground metro industry evolves such a way to adopt different construction and design technics as per the site condition, type of project, availability of material and engineering solutions.

Method and techniques are currently used in cut and cover tunnel and station construction have evolved under the influence of environmental factors at the work site. Complexity and land availability for execution the work is also a major factor to establish the construction and design methodology. Contractors are commonly using Cut and cover technics for stations, Corridors and Ramps. Usually construction sequence is followed as identification and relocation of utilities; installation of earth retaining system; installation of temporary traffic decking; excavation till the bottom; and construct the station box. Cut and cover technique is still being continued for many The Bridge and Structural Engineer

Metro Corridors, where feasible, from cost considerations, at present, where ever cost permits, in thickly built-up areas with narrow roads and accommodating ground EPB (Earth Pressure Balancing) or Slurry TBMs (Tunnel Boring Machine) are being used for tunnelling in Corridors. Where land & existing structures/ facilities create problems, metro station platform is being built by using NATM (New Austrian Tunnel Method).

Underground metro structures are commonly being built by using Diaphragm Wall (DW) either by top down or bottom up construction. Also, where sufficient land is available, for construction of pre-installed temporary retaining system for water and soil retaining system are used, with cast in situ permanent corridor and station.

Construction Methodology Construction techniques in Underground Corridors and station boxes are adopted considering parameters like geology, availability of space, depth of excavation.

Construction of Box can be done using either Topdown (as done in Kolkata N-S Metro) or bottomup or combination of both, as done in Kolkata EastWest (EW) Metro stations, first Indian Metro under a major river.

Fig. 2: Kolkata East-West Metro Tunnel https://www.railway-technology.com/projects/east-west-metrounderground-twin-tunnels-kolkata/

Bottom-up method The main site is excavated, with ground support as necessary, and the station box is constructed within. The station is being constructed with castin-situ concrete. The trench is then carefully backfilled above the tunnel roof and the surface is restored.

Top-down method Here side support walls and cap beams are constructed from ground level typically with slurry walls, or secant piles or using other techniques.

Shallow excavation allows making the station roof of in situ concrete. The surface is then restored except for corridor/ station access openings. This allows early reinstatement of roadways, services and other surface features. Excavation then takes place under the permanent station roof, concourse and base slabs is constructed, later on. In two sides of station box Excavation up to roof slab may be using strutted excavation (like soldier pile and timber lagging) which is dependent upon top soil condition.

Cut & Cover Method

Fig.1: Cut and cover construction (Bottom-Up) The Bridge and Structural Engineer

Kolkata metro had to deploy different types of design and construction techniques to suit the availability of material (mostly indigenous, from cost considerations), site conditions and to keep future provisions. The cut and cover stretch have a box configuration built either with DW, heavy duty sheet piles, contiguous bore piles, soldier piles (HVol. 48 | Number 4 | December, 2018

13

pile) and timber lagging. Few of these walls like DW or contiguous bore piles or continuous secant piles can be used both as temporary and permanent structures.

Diaphragm Wall (DW) The continuous diaphragm wall is a structure formed and cast in a slurry trench. The trench excavation is initially supported by either bentonite or polymer-based slurries that prevent soil incursions into the excavated trench. The term “diaphragm walls� refers to the final condition when the slurry is replaced by tremie concrete that acts as a structural system either for temporary excavation support or as part of the permanent structure.

The main advantages of DWs are: 1.

2.

3.

4.

5.

Increased wall stiffness compared to sheet piles.

Less noisy construction (use of hydraulically operated Kelly is less noisy than Mechanical Clamp shell bucket. In the first Indian metro NS both were used.

Can be used both as temporary and permanent wall. For permanent structure can also be used as Vertical loads besides earth and water pressure.

Provision for future Structures can also be kept as were done in First metro like cross tunnel below, to treat as foundation of future flyovers in line with City Master Plan.

Water tight (lately with improved design approach leaking through joints reduced considerably. In seventies steel tubes used at junction of two contiguous DWs where now specially made water tight joints with neoprene membrane between two specially made male / female form of steel sections are being used).

are formed by constructing intersecting reinforced concrete piles. The piles are reinforced with either steel rebar or with steel beams and are constructed by drilling through strata (can be a combination of RCC & PCC piles in case of temporary shoring walls). Primary piles are installed first with secondary piles constructed in between primary piles once the latter gain required strength. Pile overlap is typically depended on verticality tolerance rig and depth of pile.

The main advantages of secant pile walls are: 1.

2.

3.

4.

5.

6.

Increased alignment flexibility.

Increased wall stiffness compared to sheet piles.

Can be installed in difficult ground (cobbles/ boulders).

Less noisy construction.

No need to install timber lagging.

Reduced water leakage.

The main disadvantages of secant pile walls are: 1.

2.

3.

Verticality tolerances hard to achieve for deep piles.

Total waterproofing is very difficult to obtain.

Increased cost compared to sheet pile walls.

Contiguous Pile Contiguous pile walls are formed by constructing a line of circular reinforced concrete piles with a

The main disadvantages of DW walls are: 1.

2.

Requires special equipment.

Complete water tightness at junction of contiguous panel is difficult to achieve.

Secant Pile Secant pile wall can be temporary or permanent structure in underground works. Secant pile walls

Fig. 3: Open excavation

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gap typically of as per design requirement. They may be constructed using segmental temporary casing and conventional heavy-duty rotary drilling tools or by continuous flight auger techniques.

Reinforced concrete guide wall can be constructed at piling platform level to aid positional and verticality tolerances, if required.

Concrete piles constructed with full-length reinforcement cage.

In tank area the shoring wall was formed on embankment side with contiguous timber pile of 16 m long on one side. Local material was used with joint at the middle (N-S Metro Kolkata Ref. Fig.) The main advantages of Contiguous bored pile walls are: 1.

2.

3.

4.

Plan footprint flexibility.

Load bearing capacity.

Can be installed in difficult ground.

Economy compared to Diaphragm and Secant pile walls.

stages and installing lagging followed by backfilling and compacting the void space behind the lagging. Moment resistance in soldier pile and lagging walls is provided solely by the soldier piles.

Passive soil resistance is obtained by embedding the soldier piles beneath the excavation grade. The lagging bridges and retains soil across piles and transfers the lateral load to the soldier pile system.

Soldier pile and lagging walls are the most inexpensive systems compared to other retaining walls. It is also very easy and fast to construct.

The major advantages of soldier pile walls are: 1.

2.

3.

4.

5.

6.

The main disadvantages of bore pile walls are: 1.

2.

3.

Verticality tolerances may be hard to achieve for deep piles.

Waterproofing is difficult to obtain.

Increased cost compared to sheet pile wall.

Soldier Pile Soldier pile and lagging walls are some of the oldest forms of retaining systems used primarily in shallow excavations. Soldier pile walls have successfully been used since the late 18th century in metropolitan cities like New York, Berlin, and London. The method is also commonly known as the “Berlin Wall� when steel piles and timber lagging is used. In N-S Metro top 3m, in general, Soldier piles and timber lagging used.

Alternatively, caissons, circular pipes, or concrete piles can also be used as soldier piles but at an increased cost. Timber lagging is typically used although reinforced concrete panels can also be used.

Soldier pile walls are formed by constructing soldier piles (rolled I Beam used in N-S Metro) at regular intervals followed by excavating in small The Bridge and Structural Engineer

Fast to construct.

Cheaper when compared to other systems.

Installation is versatile and adjustments can be made in the field easily to accommodate changes.

Lagging construction can be very quick.

Construction of walls does not require very advanced construction techniques.

Common lagging materials include timber, shotcrete, precast concrete panels, or steel plating.

Permanent transportation walls usually utilize precast concrete panels while temporary soldier pile walls utilise timber lagging.

The major disadvantages of soldier pile and lagging systems are: 1.

2.

3.

4.

5.

They are primarily limited to temporary construction.

Cannot be used in high water table conditions without extensive dewatering.

Control base soil movements.

Poor backfilling and associated retaining systems. Ground losses can result in significant surface settlements.

They are not as stiff as others.

Sheet Piles Interlocked sheet piles form a wall for Permanent or Temporary lateral earth support with reduced ground water in flow appropriate, if requirement to withstand high pressure anchors can be introduced to provide additional lateral support.

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15

but the noise of driving restricts the use in urban areas. Concept is to design narrow, interlocking sheets that can be connected and driven into ground to form a wall. Stability and strength are defined by the shape and materials of the sheets. Steel is supposed to be most appropriate material if the requirement is to withstand large bending moment and pressure.

elements (incl. sheet pile walls, diaphragm walls) •

transferring lift forces resulting from construction (e.g. temporary anchoring of bottom plates, anchoring of stays, test loading systems, etc.)

Major Advantages are: a) b) c) d) e)

Light to easy lifting and handling.

Sheeting is reusable and recyclable.

Long life for both under and above water.

Length is adaptable.

Stronger joints to withstand pressure.

And disadvantages are: a) b)

Most difficult to install in rock or in boulder bed.

Driving cause’s noise and vibration problems for neighbouring areas.

For N-S Metro, concept was prepared by Russian Engineers and sheet piles were proposed for shoring. During that period in India, available length of sheet piles were of 7 to 8 metres and the section modulus was not good enough to use in medium to deep excavation. It was proposed to import appropriate length with required section modulus. However Indian Engineers replaced the proposal of imported sheet plies with DW to save cost and Foreign exchange.

Ground Anchors Ground anchors are used to arrest the high stresses due to ground and water pressure. Ground anchors are usually considered as a temporary system.

Temporary ground anchors are applied for carrying high tensile forces onto the load bearing soil stratum in a limited period of time (up to 2 years).

A temporary ground anchor is made of root length, rod (free anchor length) and anchorage. Temporary anchors are primarily applied for: •

supporting various types of temporary retaining walls, incl. sheet pile walls, secant pile and diaphragm wall designed as support systems for deep excavations;

•

supporting various types of permanent excavation support systems/construction

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Fig. 4: Semi-integrated Box Structure-Used in N-S Metro (Par)

Major advantage of ground anchors is, it provides the unobstructed excavation within station area.

However, it is observed in many cases that theoretical bond between ground and soil mass is much more than actual bond value which is dependent to quality of workmanship.

DW: Different approach of design & construction For the design of underground corridor and station, use of DW (used in N-S Metro in seventies and is being used till date. The difference is the basis of design approach) can be in three different ways such as a)

As temporary structure used only to facilitate excavation (strutted) and construction of independent Box for Corridor and station (First Metro is primarily based on this approach).

b)

As semi-integrated, which means that DW will be used as temporary structure during construction and will take total earth pressure The Bridge and Structural Engineer

while Box to with stand only water pressure.

Part of N-S Metro used this approach. c)

DW used as load bearing structure both during Temporary and Permanent stage (Recent Trend).

Top down construction technique with DW Top down construction technique is adopted where geology is sand, soil, soft material is available up to substantial depth. To optimise construction cost and increase the execution rate permeant wall of station box is also designed as a temporary earth retaining system as DW. DW usually designed for active pressure during the construction stages and at rest pressure for permanent stage including water pressure both for construction and permanent stage.

In few Metro projects DW is designed for soil pressure i.e. active and at rest soil pressure, with provision of weep holes in DW to avoid pore water pressure on DW. To retain the water pressure separate skin wall with wall built with bottom up construction. This construction, methodology can be adopted where water table is significantly below the ground level and station is proposed in green field area. During the construction stage no major water ingress is expected in station excavation, otherwise it may lead to settlement in nearby area.

z

Casting of roof slab and backfill the excavated portion with provision of openings of appropriate size in slab for future operations including excavation and concreting.

Bottom up construction technique When good quality of rock is available at shallow level and/or site condition is favourable for open excavation, bottom up excavation is adopted for construction. This approach is also used in clay, like the system adopted in N-S Metro. Excavation in this case is being carried out using struts in NS Metro and struts and anchors for Mumbai Metro.

In this technic excavation need to be carried out till base slab and subsequently construction of base slab, concourse, and roof slab is being carried out.

One good advantage of the bottom up construction is that good quality work is delivered with good water proofing.

Construction stages for top down execution are as given below: z

Diversion of traffic from construction site.

z

Installation of DW in two sides of station box.

z

Excavation up to roof slab may be using strutted excavation (like soldier pile and timber lagging) which is dependent on level of roof slab.

z

Divert back the traffic within the station box area, to normalize the existing traffic movement.

z

Excavate till concourse and base slab and cast as per design.

Major advantages of top down construction are one can avoid completely temporary works i.e. shoring system (except where top soil is of poor quality) also before excavation traffic can be placed in after casting of roof slab and road can be reinstated.

The Bridge and Structural Engineer

Fig. 5: Combination of struts, side anchors as applicable

Fig. 6: Excavation works for installing DW after blocking traffic close to building Vol. 48 | Number 4 | December, 2018

17

Bottom up construction technique is generally adopted where hard strata available within an excavation Zone at shallow depth. It is expected that excavation till the bottom shall be carried out with temporary shoring system. Excavation could be strutted excavation or anchor excavation. As a temporary retaining system secant pile, sheet pile, bored pile, solder pile or retaining wall can be adopted. Adoption of any methodology is also depending on the water tightness requirement, geology, and construction practicality. One good advantage of the bottom up construction is that good quality work is delivered with good water proofing.

Common issues faced during the execution of temporary works: z z

z

z

z

To ensure the verticality of DW panels.

To ensure the adequate lap joints between panels.

To ensure the quality of DW while pouring the concrete in water filled drilled hole.

To set the drilling and termination criteria for panels.

To ensure the water tightness, as far as practicable.

Brief details of DW & RCC box structure of First Metro of India

types, one for top strut (for solder pile and lagging using wales) and the second type was at deeper levels with heavier sections. The struts and wales were re used. As the design was based on empirical formula the strut forces were measured as excavation proceeded, using the strain gauges and pressure cells. It was interesting to note that the strut forces measured at general matched with design values.

A stretch in one of the sections (section 11) was constructed as a semi-integrated construction, where the top and bottom slab was integrated with diaphragm wall (Fig.). A gap of 75 mm was kept between side wall box (a structural element),and the diaphragm wall, and permanent box is designed for water pressure. While it has the advantage of lesser width of construction, it imposes stricter control on diaphragm wall. There were number of changes in the corridor and station design due to site and design issues. Numbers of such problems are indicated below.

Under the existing railway bridge, which had open foundations on loose sand layer, a special procedure had to be adopted to ensure the safety of the bridge (Fig.). The corridor divided for up and down track between two spans of ROB, DW constructed using special equipment as per local practice which can be accommodated in restricted height, between bottom edge of bridge structure and road level.

The underground structure is a RCC box of 500 mm thick side wall, top and bottom slabs, and a row of column at centre (also 600 mm in place) of box corridor (column location at station as per design requirement), spaced at 3 m with top and bottom longitudinal beams, for bottom up construction. A gap of 500mm was kept between the diaphragm wall and the to-be-filled-with-earth subsequently (Fig.). This gap takes care of inaccuracy in the construction of diaphragm wall, though it also increases the overall width of construction. The box was constructed between two 600/800 mm thick DW, as applicable The Excavation was carried out between two rows of DWs after propping them against each other by steel struts. The design of compression struts accommodated earth pressure on diaphragm wall.

The strut sections were standardized and made with rolled sections joining them with battens as per design. While standardization, there were two 18

Vol. 48 | Number 4 | December, 2018

Fig. 7: Cross section Arrangement of Diaphragm Walls and struts for Box Structure The Bridge and Structural Engineer

Another special case was near Shiv-Kali temple, where to avoid shifting of the temple which could have given rise to serious socio-religious apprehensions, the up and down alignments were taken in independent boxes, and constructed using normal approach for strutted excavation with profile to suit site. Fig in the corresponding page shows the same.

In the general tank stretch non-availability of sheet piles and equipment for diaphragm wall on time, it self-forced the decision for open excavation. It had serious issues on slope stability.

Moreover, movement of heavy equipment was also not possible in the area for using precast or bored piles for interception. Hence, open cut with timber piles to support the slope of excavation was the method adopted. Timber pile of 14/15 m deep with joint of two piles at middle was used. Piles were also supported by inclined struts Box structure was

Fig. 8: Open excavation in General Tank Area near a Temple to address slop stability issues

constructed using cast-in-place concrete in open environment.

Advancement in design and construction approach in underground metro Design method adopted in first metro of India during seventies: During seventies based on practices followed in different countries, experience gained across the World, analysis, particularly for rigid structures like DW was adopted in N-S Metro.

Distribution of earth pressure corresponding to the soil pressure at rest (k o ) on either side of the diaphragm wall is one of the most important design considerations. Strut spacing is influential for the earth pressure development and rigidity of the diaphragm wall itself. The earth pressure models for both cohesive and non-cohesive soils which were similar to that of Peck’s apparent earth pressure diagram. An instrumentation program concurrent with the execution with real-time feedback fixed and validated the lateral pressure due to building surcharge with the execution with real-time feedback fixed and validated the lateral pressure due to building surcharge. It was considered as 5.5 t/sqm at a minimum distance of 2 meters horizontally and 1.5 m vertically below the ground surface. This pressure was presumed to act continuously along the side of the diaphragm wall wherever applicable. Lateral pressure due to road surcharge had been divided into two mutually exclusive cases, during construction and service.

Stability of the excavation, ground movement, control of water into the excavation area, effect on adjoining structures and design of structural elements such as diaphragm wall and struts are distinct, yet inter-related features in the design of braced excavation. The depth of penetration of supporting wall below bottom of cut was determined from the consideration of stability against bottom heave (Fig.). The factor of safety against bottom heave was kept as not less than 1.5, as per formula.

600 mm thick wall (800 mm in some areas) was cast mostly in 3 m panels into bentonite slurry trenches. Excavation was done using imported Clamp Shell Bucket (4t wt. and mechanically operated, with absolute plumb) in one package and others by hydraulically operated Kelly grabs.

Fig. 9: Timber Pile Arrangement The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

19

Approach being adopted currently in India

Fig. 10: Distribution of earth pressure

F.O.S

Cu4Nc+r3D2+r4D1+Σ Cu(H+D2+D1)/D1

Σ r(H+D +Dr)

>1.5

2

Depth of penetration was in general is 3-4m. In certain cases, depth has to increase to 7-8 meter, due to soil condition or to carry additional loads of Flyover in future or for planned high rise buildings in future over the Metro Section. Panel widths were also increased in few places up to 6 meters with two rows of Struts, as par site requirement. Struts were located at mid of each Panel except for wider panels and three or four layers depending on depth/ as par site requirement. In N-S Metro, different design approaches were adopted depending upon Site/Design condition / requirements, like Cross DW, Bored Cast in situ RCC pile walling, Topbottom Construction (first time in India) for a length of 56 metres.

Remedial Measures Cases of leaning of Diaphragm walls towards cut side occurred in number of sections and maximum infringement was in the tune of 800 mm. As remedial measures enveloping DWs were built outside. And tilted DWs were dismantled.

Where sides of DW trench collapsed during concreting (due to mechanical failure of cranes), enveloping DW system were too introduced. In places of considerable honeycombing and exposure of reinforcements steel plates were welded.

To retain a Temple in middle of Road, enveloping DW were built around the Temple and entry provided through top temporary decking. In addition appropriate design was adopted to construct the underground Corridor in number of sections and keeping the safety arrangement like grabbing under water by filling the excavation, using sand bags for protective measures, underwater grouting and others.

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Vol. 48 | Number 4 | December, 2018

Now designers are commonly using finite element base software for more accurate and optimized design. Because of advancement of technologies engineers are able to used more sophisticated tools to handle different complex scenario. Good engineering design includes analysis of system performance as part of design development. Many tools are available to design details of underground structures-For example, thickness of supports or appropriate size and location of ventilation shafts.

Empirical and analytical design methods, ideas and procedures based on experience, building codes, and analytical and computational software packages all contribute to optimal design of underground structures. However, their effectiveness directly correlates with the quality of data input and the knowledge base and experience of those applying the tools.

Empirical design methods rely on quasiquantitative approaches to material characterization based largely on experience-driven judgments. They are not necessarily based on fundamental mechanisms of ground and structure behaviour. For example, soil and rock classification systems are based on the comparison of observed material behaviours from the infrastructure site to similar observations made elsewhere. Behaviour is predicted based on those comparisons, but the underlying reasons for the behaviours may not be well understood. Even so, the soil and rock classifications based on empirical characterization often inform support requirements and design specifications. In some cases, empirical characterization may be based on a large number of prior observations, and resulting conclusions may be robust. In other cases, few data exist to enable comparisons, and empirical characterizations may be more similar to “best guesses”. Empirically based conclusions can be considered first-order estimations, and further observations may be necessary to confirm or refine those estimates. In other words, they can be used to interpolate but not extrapolate. Improper use of empirical tools can result in safety hazards, poor performance, or unnecessary expenses. Educating professionals about the limitations of empirical methods is one way to improve their use. Improving the databases of observations and the methods for their expansion is another.

The Bridge and Structural Engineer

Comparison of Design and Construction Approach including Cut & Cover and Tunnel in 1970s and 2010s EAST – WEST METRO (2009 s -)

NORTH – SOUTH METRO (1974 s -)

Bottom-Up method adopted, but top-down method was also used in small stretch.

Vertical retaining DW ground supports and inside concrete box. In some portions, the retaining DW was semi-integrated with inside concrete station box.

Rigid box. Retaining DW designed for full earth pressure and other loadings. In-situ concrete box wall designed for hydrostatic pressure Depth of station box are similar for all stations In Central, Island and Side types platforms. Others were Island Platform Temporary DW retaining wall and H-pile with lagging were used for C&C link tunnel. Temp DW was semi-integrated with the inside concrete box tunnel in some portions.

Analytical methods of analysis.

Earth pressure calculations using Terzaghi-Peck empirical formula Strut-waling support system for Bottom-Up technique Temporary traffic decking used at most locations.

More width required for constructing temporary earth retaining DW Conventional system used with Kelly-grab attached to crane and also mechanical grab, clamp shell bucket (4t) for one section.

Tube form articulation at panel joint.

Thickness of DW 0.6m-0.8m.

All round PVC water bar at box-box joints.

Grade of concrete M20/M25 Cut & Cover box tunnels linking stations. Bored tunneling for short critical stretch using conventional TBM and blade shield tunneling.

Precast cylindrical concrete/ cast iron ribbed lining jointed by high tensile bolt. Short portion using precast segmental lining.

Analytical methods using empirical formula for lining.

Earth pressure calculations using Terzaghi-Peck empirical formula Link tunnels generally C&C box, bored tunnel portion using Blade Shield tunnel machine and double ‘D’ tunnel by TBM also used.

Conventional TBM with air pressure 0.5-1 atmosphere.

Conventional system for bored tunnels Conventional TBM with air pressure regulation.

M40 grade concrete

Top-Down method for stations and Bottom-Up for Crossover box and access shaft.

Permanent diaphragm wall earth retaining system for Bottom-Up box.

Rigid box subject to earth pressure at rest and other loadings.

Stations on each side of river are deeper than others Island type platform for u/g stations. Island + side types platform at Howrah.

Bored tunnels linking u/g stations.

Numerical analysis for construction and permanent stages.

Soil-Structure Interaction models employed using Plaxis program.

Seismic modeling performed for u/g structures Temporary strut-waling system reduced by TopDown technique Limited use of temporary decking during construction.

Less C&C box footprint in Top-Down technique Hydraulic rig with grab for DW. Special equipment for monitoring trench profile.

Stop end and water bar used at DW panel joint.

DW panels up to 1.5m thick and ~ 60m depth.

Membrane waterproofing to base and roof of box.

Grade of concrete M40 Bored Tunnels linking the u/g stations for entire corridor.

Segmental precast concrete tunnel lining, jointed by high tensile bolts.

Analytical + Numerical analysis for segmental lining subject to earth pressure and other loads.

Soil Structure Interaction analysis using Plaxis program Seismic analysis performed Radial segment joints EPB Machine for bored tunnels.

Sensor fitted face pressure monitoring.

Hydraulic segment erector.

Two level gaskets for joints.

VMS guidance and Safety features.

M40/M50 grade concrete

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

21

Ground Improvement Technologies It is often necessary or productive to temporarily or permanently change soil or groundwater properties during underground construction to ease facility design, construction, or operation. For example, ground freezing can temporarily turn a weak, saturated soil into a solid and nearly impermeable material; dewatering can ease construction problems both in terms of water flow and soil stability; and grouting can be used to stiffen or change the permeability of soils. Ground modification techniques and the development of new materials used for geo-environmental and geomechanical applications (e.g., bio- and nanotechnologies; NRC, 2006) are active areas of research and field application. Furthering application of established methods (e.g., jet grouting and compensation grouting), as well as developing new approaches and materials, offer the potential for cost reductions and performance improvement. However, as for trenchless technologies, application of new ground improvement technologies may outstrip theoretical understanding of the methods, meaning that application of these techniques in design may not be optimized. Further research and development are needed to improve existing methods, enhance understanding of their application, and allow better engineering with, for example, in situ biotechnologies, nanotechnologies, and other ground improvement and remediation techniques that can reduce the resource use and be gentler on the environment than can more traditional construction methods.

Monitoring During Construction Geotechnical instrumentation refers to the instruments used to monitor geotechnical projects or sites requiring such monitoring. Geotechnical instrumentation and monitoring are essential for the successful completion of a geotechnical projects. Limited geotechnical instrumentation may be needed for simple projects but the demands on geotechnical instrumentation and monitoring can be very demanding for critical projects such as tunnels, slopes, and excavations next to sensitive structures. Real time monitoring has help industries to understand the response of sensitive structure due to nearby major station excavation.

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The principal parameters of interest in geotechnical monitoring are: (1) structural and soil deformations, (2) stresses acting on structural elements (wall and bracing), and 3) ground water pressures and inflows.

Inclinometers, piezometers and optical surveys have been used to monitor the majority of the projects compiled in this database. Generally, the quality of the available instrumentation was dictated by the project requirements. The quality of data in more recent projects tends to be better since computers have facilitated data acquisition and archiving. In sensitive deep excavations, inclinometers and surface settlement surveys are used in almost all the projects. Thus, inclinometer deflections have been more widely used for comparisons between cases due to their availability in almost all the archives. Water levels and piezo metric levels can also be critical.

Fig. 11: Typical Cut and cover Station box

In a many project, strain gages or load cells were used to monitor strut loads (used for NS Metro).

In very few projects strain gages and embedment gages were used to deduce moments and axial forces in the slurry wall.

Sometimes, single point extensometers have been used to measure subsurface settlements, but multipoint borehole extensometers have only rarely been used. Earth pressure cells have been used only in test programs.

Monitoring strategies are not significantly different from city to city but the extent of instrumentation does depend on local practices.

The Bridge and Structural Engineer

Way Forward

Fig. 12: Typical NATM Station BOX

Future development is planning to reduce economic & financial cost, social and environment. As such Construction cost is not only factor, delays in construction resulting commuters delay, interruptions of Business Activities, cost and availability of Tenants, loss of local business etc. all part of Construction Methodology. In developed countries like USA, to develop faster construction to reduce time and cost, precast panels are being planned to use in slurry trench. The approach improves quality, pre-erection waterproofing for soil face, required finishes on operation side besides bearing plates, keys, dowels and recesses being included during casting of panels. Precast deck panels can also be introduced for permanent decking with better quality and less interruptions to public. As such precast concrete temporary decking already used in large scale in N-S Metro in Seventies are adopted.

References

Fig. 13: Typical NATM Platform to Station BOX Connection

NATM Station NATM Station generally proposed when geology is favourable and space to accommodate the station box is limited. In many projects in India tunnel is passing outside the cut and cover station box. In such a case access to tunnel from station box is made with NATM excavation, also widening of exiting TBM tunnel is need to make with NATM excavation technique to accommodate the platforms.

The Bridge and Structural Engineer

1.

Kolkata Metro – Planning and Design by B C Roy et. al.

2.

Kolkata Metro – Design & Construction by B C Roy et. al.

3.

Behaviour of Braced Cut in Soft Soil Condition– Calcutta Metro by B C Roy & N Som.

4.

Urban Mass Transit System and Metro Kolkata

by H K Sharma, B C Roy.

5.

Kolkata Metro including the East West Metro

by H K Sharma, B C Roy & B Dewanjee.

Vol. 48 | Number 4 | December, 2018

23

SOIL-STRUCTURE INTERACTION ANALYSIS OF EMBEDDED RETAINING WALLS FOR UNDERGROUND METROS

Dr. Makarand G. KHARE

Sudheer Kumar SEEKARAP PALLI

Associate Director AECOM India Pvt Ltd Mumbai, INDIA Makarand.khare@aecom.com

Makarand Khare, received PhD (Engineering) from Indian Institute of technology Madras, Chennai, India. His areas of specialisation are Geotechnical Engineering, SoilStructure Interaction, Finite Element Analysis, and Underground Structures. He has worked as a Geotechnical Expert in number of metros.

Engineer II AECOM India Pvt Ltd Mumbai, INDIA ss.kumar@aecom.com Sudheer Kumar received his Civil Engineering degree from National Institute of Technology Tiruchirappalli, India. He has worked as a Geotechnical Engineer for Underground Metros.

Abstract

1.

The construction of underground stations with cut and cover method requires a stringent control of ground movements. The allowable ground movement governs the selection of embedded wall and propping scheme. The paper compares the deflection of embedded walls using finite element method (FEM) and subgrade reaction method (SRM). The analysis shows that the wall deflection and ground movements predicted by SRM are likely to be more than that predicted by the FEM analysis. At sites where structures having poor condition / sensitive / heritage characteristics exist in the close vicinity of excavation the prediction of ground movements becomes paramount for the design and construction of propped embedded wall.

At such sites it is beneficial to use sophisticated design tools such as FEM to model soil-structure interaction.

The construction of an underground metro station using cut-and-cover method requires deep excavations in the congested urban environment.

At sites where major depth of the excavation is in soft ground, a multi-propped diaphragm wall is preferred as a temporary support during excavation and permanent support during service life.

Diaphragm wall offers water-tightness, minimum noise and vibration disturbance during installation, and is a proven construction method for lateral earth support. Diaphragm wall also enables flexibility in terms of construction sequence.

However, where the rock is relatively shallow compared to rail level, installation of diaphragm walls becomes challenging then secant piled walls supported with struts and / anchors may be a preferred option. The analysis and design of embedded propped wall requires a thorough understanding of site geology, construction sequence and allowable ground movement. In the first section of the paper a case of propped diaphragm wall is presented to illustrate the influence of method of analysis to account soil-

Keywords: underground metro, cut and cover structures, diaphragm wall, secant piled wall, ground movements, subgrade reaction method, finite element method 24

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Introduction

The Bridge and Structural Engineer

structure interaction. In the second section a case of secant piled wall is presented to demonstrate how the method of analysis impacts estimation of ground movements behind the wall and thereby the potential damage to the nearby existing buildings and structures. The cases described in this paper are based on various metros under construction/ operation.

2. Soil-Structure Interaction Analysis of Embedded Diaphragm Wall The methods of analysis for an embedded retaining wall can be broadly classified as limit equilibrium, subgrade reaction method (SRM) or pseudo-finite element and finite element method (FEM) or finite difference method (FDM). The FEM and FDM consider the interaction using various constitutive models for soil and structure. The limit equilibrium approach may be used for preliminary design of multi-propped wall without prestressing in anchors (Tamaro and Gould, 1992). A case of multi-propped diaphragm wall in sandy soil is presented here using subgrade reaction method and finite element method. A case of bottom-up construction sequence for a typical underground metro station is modeled.

Appropriate surcharge due to construction equipment, adjacent buildings and traffic loads are considered in the analysis. The wall deflection, bending moment and strut forces obtained from SRM and FEM are compared.

crystalline rocks mostly of charnokite series.

The ground water table is shallow and rises near to ground level during rains. The generalized geological profile is shown in Fig. 1. Table 1 shows geological profile and engineering properties of soils and rock considered for the purpose of this paper.

2.2 Construction Sequence In the present paperbottom-up (BU) construction sequence is analyzed with SRM and FEM. A typical cross-section of the station excavation using BU construction sequence is shown in Fig. 1. The maximum excavation depth isabout 19 m below ground,

2.1 Site Geology The geology consists of alluvial soils overlying the bedrock. The average depth to bedrock varies from 20m to 25m. The alluvium consists of silty sand, sandy clay, silt and occasional gravels and is underlain by

Fig.1: Geological profile and schematic of bottom-up construction

Table 1: Engineering properties of soils and rock Depth (mRL)

+2.8 to -2.2 -2.2 to -9.2 -9.2 to -17.2 -17.2 to -22.2 -22.2 to -27.2 Below 30

Soil Unit

Engineered backfill SM 1 SM 2 SM 3 SM 4 HWR MWR

Bulk Density γ (kN/m3)

Poisson’s Ratio

Cohesion, c’ (kPa)

Frictional Angle, Φ ’ (°° )

Young’s Modulus, E’ (MPa)

Interface strength, Rint

20

0.3

0

35

35

0.67

18 19 20 21 22.5 23

0.3 0.3 0.3 0.3 0.3 0.25

0 0 0 0 5 800

30 31 33 36 42 36

15 20 30 50 100 1400

0.67 0.67 0.67 0.67 0.7 0.7

The Bridge and Structural Engineer

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Table 2: Slab and strut properties

Identification

Diaphragm wall (1m thick) Base Slab (1.1m thick) Roof slab (0.9m thick) Concourse slab (0.55m thick) S1 S2 S3 S4 S5 .

EA [kN/m] 3.165 3.478 2.855 1.740 6.293 6.293 6.293 7.240 9.102

× × × × × × × × ×

107 107 107 107 106 106 106 106 106

and the excavation is retained by a 1m thick, 29 m deep reinforced concrete diaphragm wall founded in highly weathered charnockite. The geometrical and material properties of diaphragm wall, slabs and struts are given in Table 2. A 10 m wide traffic surcharge of 20 kPais applied at a distance of 1m away from the wall. The effect of building foundations near the excavation is considered by applying a 10 m wide, 100 kPa surcharge at ground level at a distance of 11 m from the edge of diaphragm wall. The construction stages are described in Table 3.

The groundwater level outside excavation is considered at ground level (which is a common scenario for most of the metros in India) and groundwater profile is considered to be hydrostatic throughout the period of excavation.

2.3 Subgrade Reaction Method (SRM) In this approach, soil-structure interaction is analyzed as a one-dimensional problem. The diaphragm wall is considered as a continuous beam of unit width and soil is modeled by a set of unconnected horizontal springs; any structural supports, such as props or anchors, are also represented by simple springs (Carrubba and Colonna, 2000).

In spite of its saving in terms of computer resources over more rigorous procedures, the SRM does not provide a complete behavior of soil movements and overall stability, due to the reduction of the original problem from 26

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EI [kN-m²/m] 2.635× 3.510× 1.925× 4.380× -

106 106 106 105

w [kN/m/m]

ν [-]

Strut Spacing [m]

24.00 26.40 21.60 13.20 -

0.20 0.20 0.20 0.20 -

6 6 6 6 6

Table 3: Construction stages for Bottom-Up Method Stages

Construction Sequence

1

Traffic (20 kPa) and building surcharge (100 kPa) are activated Install Diaphragm walls Excavate to 0.5m below strut (S1) and Install strut (S1) at level 2.0mRL Excavate to 0.5m below strut (S2) and Install strut (S2) at level 0.0mRL Excavate to 0.5m below strut (S3) and Install strut (S3) at level -3.0mRL Excavate to 0.5m below strut (S4) and Install strut (S4) at level -8.0mRL Excavate to 0.5m below strut (S5) and Install strut (S5) at level -12.0mRL Excavate to level -16.325mRL Construct base slab, permanent column and concourse slab Remove struts (S5) and (S4) Construct permanent column and roof slab Remove struts (S3) and (S2) Engineered fill upto 0.5m below strut (S1) Remove strut (S1) Engineered fill to Ground level

2 3 4 5 6 7 8 9 10 11 12 13 14

bi-dimensional to one-dimensional. Some implementations of SRM provide for limited interaction between springs making a significant improvement in the approach (Pappin et al., 1985). Nevertheless, these procedures have problems in dealing with soil-wall friction and therefore often neglect the shear stress on the wall or make extra assumption to deal with it (Potts, 1992).

The Bridge and Structural Engineer

The major drawback of SRM is it does not capture the effects of soil arching on account of wall deflection during excavation (CIRIA, 2003). Commercially available software is used to analyse the construction sequence using SRM. The key features of the SRM analyses are:

The key features of the FEM analyses are: a) The diaphragm wall is assumed to be “wished in place” and sequential excavation are simulated by removing the soil clusters from the front of the wall and activating the strut and slab elements, b) Diaphragm wall, slabs, columns and barrettes are modeled using plate element with elastic behavior,

a)

Soil and rock behavior is assumed elastic,

b)

Diaphragm wall and soil are modeled as a beam and springs respectively,

c) Soil and rock are modeled as Mohrcoulomb materials with Elasto-Plastic behavior,

c)

The roof, concourse and base slabs are modeled by applying rotational fixity at the respective elevation,

d) 15 noded triangular elements are used for soil and rock,

d)

The water table at each stage is assumed to follow the excavation profile with hydrostatic pressure during all stages of excavation,

e)

Struts are modeled as strong elastic springs.

2.4 Finite Element Method (FEM) FEM discretizes the geometry of problem into many small regions, or finite elements, which are connected at a discrete number of nodes located on their boundaries. FEM analyses the problem of a continuous body with an infinite number of unknowns, to that of a discretized body with a finite number of unknowns, corresponding to the displacement components of the nodes. The major problem dealing with finite element analysis are: geometric modeling and discretization, modeling of installation, excavation and pore pressure equalization, choice of constitutive model and associated soil parameters, and finally computational difficulties (Woods and Clayton, 1992). Comparative analyseshave shown that, although simple models generally provide realistic values of wall movements, only the most complex may accurately predict soil displacements (Viggianiand Tamagnini, 1997). In this paper, the wall is assumed to be linearly-elastic and the soil continuum asa linearly-elastic perfectly-plastic material.

Commercially available software is used for finite element analysis.

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e) Struts are modeled as node-to-node anchors with elastic behavior and slabs are modeled using plate elements, f) The water table at each stage is assumed to follow the excavation profile with hydrostatic pore pressure at all stages of excavation.

2.5 Comparison of FEM and SRM Analyses The wall deflection profiles predicted from SRM and FEM are compared in Figure 2. For BU construction, the maximum wall deflection predicted by SRM is about 22% higher than that of FEM as shown in Figure 2 (a). This could be because of the fact that FEM can model arching effects behind the deflected wall. The soil arching behind wall lowers the net active earth pressure and thereby the wall deflection. As the excavation progresses below the concourse slab (i.e. below -6.2 mRL), the wall deflection increases rapidly and the deflection predicted

by FEM converges with SRM at the base slab level.

The bending moment envelopes obtained from SRM and FEM are compared in Fig. 2 (b).

From Fig. 2 (b), it is observed that the bending moment on ‘excavated side’ predicted by SRM and FEM follow identical trend and the magnitude of bending moment is comparable.

The SRM predicts slightly higher bending moments possibly because; SRM does not account the arching effects behind the wall.

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27

a) Wall Deflection

b) Bending moment envelope

Fig. 2: Wall deflection and Bending moment envelope

However, the bending moments towards retained face predicted by FEM are notably high at the roof and concourse slab levels.

In case of SRM, horizontal soil yielding is often evaluated by means of the Caquot and Kerisel (1966) earth pressure coefficients.

These coefficients refer to free displacements of rigid walls, and may be not suitable for multi propped walls when arching phenomena modifies the stress field behind the wall.

Carrubba and Colonna (2000) suggested that the mean active and passive earth pressure coefficients may be evaluated by FEM and subsequently introduced in SRM. By this approach, the results obtained by SRM and FEM may show better agreement.

The appropriate values of soil stiffness and limiting earth pressures is an important factor when analysing a problem with SRM. The major drawback of SRM is its inability to account for soil arching and to perform stability calculations. The FEM models the reduction in active earth pressure due to soil arching. Therefore the wall deflections predicted by FEM were generally lower than SRM. A comparison of various methods of analyses in initial stage of project can be useful before the detailed designs are carried out.

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3. Ground Movement Prediction – FEM and SRM The deflection of propped embedded wall results in vertical and horizontal ground movements behind the wall. The underground metro stations are oftenbuilt in the close proximity of high rise buildings, dilapidated structures, sensitive / heritage structures, critical utilities, bridges etc.

Therefore, the prediction and control of the ground movements around the proposed stations is an important objective of design and construction.

During the design phase, the ground movement prediction and its potential impact on the neighbouring existing buildings and structures is assessed to limit the impact to acceptable level.

In order to limit the potential impact, sometimes the excavation support scheme may have to be revised to make it far more rigid/stiff than that may have been envisaged earlier. In such cases a thicker wall, additional struts / anchors, ground improvement may have to be considered during design phase.

The above discussion emphasises the importance of wall movement and settlement prediction in deciding the excavation support scheme. This section of the paper compares the ground movement prediction using FEM and by empirical methods for a BU excavation sequence using secant piled wall embedded in rock.

The Bridge and Structural Engineer

3.1 Site Geology

material properties of secant piled wall, struts and anchors are given in Table 5. The groundwater table is considered at the ground level. The schematic of excavation sequence modelled in FEM and SRM is shown in Fig. 3. The secant piled wall deflection using FEM and SRM are compared in Fig. 4.

The ground comprises of soft soils (predominantly silty, clayey sand, clay of medium to high plasticity and boulders) followed by volcanic rock formation. The thickness of soft ground varies from about 1m to 15m. The major volcanic rocks are basalt, breccia, and tuff. Intertrappean sedimentary rocks such as shale are also found. The ground water table is shallow and rises close to ground level during monsoon. Table 4 shows geological profile and engineering properties of soils and rock considered for the purpose of this paper.

The key features of the FEM analyses are: a) b)

c)

3.2 Construction Sequence

d)

The excavation support is provided by 1m diameter secant piles supported by steel struts and groundanchors. The geometrical and

The secant piled wall is assumed to be “wished in place”, Secant piled wall and concrete decking are modeled using “standard beam” with elastic behavior, Soil is modeled as Mohr-Coulomb materials with Elasto-Plastic behavior, Rock mass is modelled using equivalent friction, cohesion and deformation modulus based on Hoek-Brown criteria,

Table 4: Engineering properties of soils and rock Depth (mRL)

2.1 to -0.9 -0.9 to -4.9 -4.9 to -7.6

-7.6 to -12.90 -Below -12.90

Soil Unit

Bulk Density, γ (kN/m3)

Poisson’s Cohesion, c’ Frictional Young’s Interface Ratio (kPa) Angle, Modulus, strength, Φ ’ (°° ) E’ (MPa) Rint

Fill Medium Stiff Clay Completely to Highly weathered rock Moderately weathered rock Highly Weathered Rock

20 20

0.3 0.3

0 0

26 26

10 15

0.5 0.5

23

0.3

76

38

148

0.7

24

0.3

144

49

854

0.7

24

0.3

200

54

1957

0.7

Table 5: Wall, Struts, and Anchor Properties Identification

Secant pile wall Concrete Deck Strut 1 (Steel Strut) Strut 2 (Steel Strut) Strut 3 (Steel Strut) Anchor 1 (Tie back) Anchor 2 (Tie Back) Anchor 3 (Tie Back)

Cross Section [m2]

Youngs Modulus (kN/m2)

0.06809 0.10070 0.10070 0.10070 0.00033 0.00033 0.00033

3.1600E+07 2.958E+07 2.000E+08 2.000E+08 2.000E+08 2.000E+08 2.000E+08 2.000E+08

The Bridge and Structural Engineer

Spacing Inclination [m] (Degs) 1 10 10 10 3.2 3.2 3.2

0 0 0 0 0 15 15 15

Pre-stress Free per strut Length (kN) (m) 0 0 0 0 800 800 800

7 6 5

Tension Allowed No No No No Yes Yes Yes

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29

(a) SRM Model

(b) FEM Model

Fig.3: Schematic of FEM and SRM models

e) f) g)

6 noded triangular elements are used for soil and rock, Struts are modeled as “standard beam� with elastic behavior, The water table at each stage is assumed to follow the excavation profile with hydrostatic pore pressure at all stages of excavation.

The key features of the SRM analyses are: a) Soil and rock behavior is assumed elastic, b) Secant piled wall and soil are modeled as beam and springs respectively, c) The water table at each stage is assumed to follow the excavation profile with hydrostatic pressure during all stages of excavation, d) Struts and anchors are modeled as elastic springs, e) Anchors are allowed to take tension / prestress force.

30

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Fig. 4: Secant Piled Wall Deflection Profile

3.3 Ground Movement Prediction The secant piled wall deflection profiles predicted by FEM and SRM are compared shown in Fig. 4. The maximum wall deflection predicted by FEM is 10 mm

The Bridge and Structural Engineer

whereas that by SRM is 24 mm. The reasons for lower wall deflection estimates by FEM compared to SRM are already discussed in section 2.5 of this paper. The ground movements can be readily extracted from FEM analysis. However, in the case of SRM empirical methods have to be used to predict the ground movement based on deflected wall profile. Bowles’ (1997) suggested a procedure to estimate excavation-induced ground surface settlements, which is described below: a)

Estimate the lateral displacement of the wall. Here, the wall displacement is estimated using SRM,

b)

Numerically integrate the wall deflections to obtain the volume of soil (V s) in the displacement zone,

c)

Estimate the lateral distance (D) of the settlement influence which is considered as two times the depth of slightly weathered Basalt,

d)

Compute the surface settlement at the edge of the excavation wall as, 2V s Sw =

e)

_______

(1)

D Compute remaining ground loss settlements assuming a parabolic variation of S i, from Dtowards the wall as x 2 _____ Si = Sw D (2)

( )

The above described method is used to estimate ground movements. The predicted ground movement profiles by FEM and SRM are shown in Fig. 5. It is observed that the ground s ettlement predicted by FEM is only about 8mm against 28mm predicted by empirical method.

Therefore, where the dilapidated/sensitive structures are located close to the excavation it is prudent to analyse the excavation scheme using FEM in order to have realistic assessmentof ground movements which will govern the design and construction of excavation support scheme.

The Bridge and Structural Engineer

Fig. 5: Ground Settlement Profile by FEM and SRM Methods

4.

Conclusions

The design and construction of underground stations with cut and cover method in densely urban area is often governed by the allowable ground movements. Therefore prediction of ground movement plays an important role in selection of embedded wall and propping scheme. The paper shows that the deflection of embedded walls using SRM is likely to be more than that predicted by the FEM analysis. This is due to the fact that FEM explicitly captures stress redistribution within the retained soil mass and thereby accounts for the arching effects behind the wall. However, FEM requires higher computational efforts and can be relatively complex when compared to SRM. At sites where structures having poor condition / sensitive / heritage characteristics exist in the close vicinity of excavation, the prediction of ground movements as precise as possible becomes vital for the design and construction of propped embedded wall. At such sites it is beneficial to use sophisticated design tools such as FEM. References 1.

Bowles, J.E. (1997), “Foundation Analysis and Design, 4th Ed”, McGraw-Hill Book Company, New York, USA.

2.

Caquot, A. and Kerisel, J. 1966 “Traite de mecanique des sols”, Paris Gauthier-Villars.

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31

3.

Carrubba, P. and Colonna, P., 2000 “A comparison of numerical methods for multi-tied walls. Computers and Geotechnics” Vol. 27 pp. 117-140.

7.

Tamaro, G.J., and Gould, J.P., 1992. “Analysis and design of cast in situ walls (diaphragm walls)”. Proceedings Retaining Structure, Cambridge, pp. 343- 352.

4.

Gaba, A.R., Simpson, B., Powrie, W., and Beadman, D. R., “Embedded retaining walls – guidance for economic design” Ciria – C580, 2003 Published by Ciria, London, UK.

8.

5.

Pappin, J.W., Simpson, B., Felton, P.J., Raison, C., 1985. “Numerical analysis of flexible retaining walls” Proceedings of the Numeta ’85 Conference, Swansea, UK. pp. 789-802.

Viggiani, G. and Tamagnini, C. 1997.

“Analisideimovimenti in corrispondenza di scavisostenuti da paratieancorate: alcune considerazion isull’influenza del modellocostitutivo”. In: Attidel IV Convegno Nazionale del C.N.R., Perugia, pp. 603 - 623.

9.

Woods, R.I., Clayton. C.R.I., 1992. “The application of the CRISP finite element program to practical retaining wall problems”.

Proceedings Retaining Structures, Cambridge, pp. 102-111.

6.

32

Potts DM.”The analysis of earth retaining structures”. In Proceedings Retaining Structures, Cam-bridge, 1992. p.167±86.

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

SPECIAL CONSIDERATIONS OF DEEP EXCAVATIONS AND CUT-ANDCOVER TUNNELLING IN NON-COHESIVE SOILS WITH HIGH GROUNDWATER LEVEL Frank RACKWITZ Professor Dr.-Ing. Head of Chair of Soil Mechanics and Geotechnical Engineering, Managing Director of the Civil Engineering Department, Berlin University of Technology (TU Berlin), Germany frank.rackwitz@tu-berlin.de Frank Rackwitz, born 1969, received his civil engineering degree as well as doctoral degree from the Berlin University of Technology, Germany. He has been Professor at BTU Cottbus and OTH Regensburg, Germany before becoming Professor and Head of Chair at the Berlin University of Technology, Germany. His main area of research is related to geotechnical experimental investigations and numerical modelling.

Summary The design and execution of deep excavations in non-cohesive soils with high groundwater level require special solutions to prevent uplifting of the geotechnical structures before and during the construction of the superstructure under dry conditions inside the excavation pit. An overview of suitable geotechnical solutions is given for such requirements. Some details to be considered during design and construction are presentedbased on the experience of various executed projects in the City of Berlin. Results from measurements of wall displacements, slab heaving and leakage rates indicate the necessity of robust design and construction in conjunction with sophisticated simulation as well as monitoring strategies. Special focus of the contribution is also on the application of web-based monitoring systems to complex geotechnical engineering projects.

Keywords: deep excavations, cut-and-cover tunnelling, sandy soil, high groundwater table, monitoring, anchor pile installation, web-based monitoring data management.

1.

Introduction

Since the mid of the nineties in the City of Berlin there have been built underground structures, i.e. railway and street tunnels as well as foundations The Bridge and Structural Engineer

deep embedded in the groundwater, with some extraordinary measures. The surface area of all tunnel constructions of the VZB-Project (inner city traffic tunnels in Berlin) amounts to approx.

240,000 square meters thereof trough excavations (wall-slab constructions) cover about 200,000 square meters. The excavation pits for the tunnel structures have depths of more than 20 meters and widths of more than 100 meters. All this projects lead in the mid nineties to the characterization of the City of Berlin as Europe‘s biggest construction site [1].

The essential technical part of this solution was the new 3.4 km long, four-track railway tunnel running through the city centre beneath the new government district, the Tiergarten Park, and the new development centre at the square Potsdamer Platz. Parallel to the railway line goes the national road B96 which also crosses the government centre.

So it was necessary to put the road down in a tunnel.

On the design and construction of these two tunnels, especially that for the railway line, was reported in the past [1].

A number of technical problems had to be resolved and new strategies devised at the planning stage because of the geotechnical and hydrogeological conditions in the central area of Berlin, the environmental requirements concerning groundwater conditions, and interaction with the surrounding green area and the nearby existing Vol. 48 | Number 4 | December, 2018

33

buildings. Several methods of tunnelling constructions in cohesionless soils with high ground water level were applied, such as caissons, shield driven tunnels and trough-type excavations (cut-and-cover tunnels) [1, 2, 3].

Quality assurance and management is an important issue of complex geotechnical engineering projects.

It includesusually extensive monitoring systemsin the frame of the geotechnical observation method to ensure the quality of the constructions and to control design predictions. The impact of a big geotechnical project on the urban life and on the environment wouldn‘t be minimized without a sophisticated project and ground water management. Based on the experience with the huge projects beginning in the 1990s a number of improvements on design, construction execution, numerical simulations, and monitoring has been made which will be reported here.

2.

2.1

Deep excavations and cut-and-cover tunnelling methods Soil and groundwater conditions The geology of the central area of Berlin is characterized by saturated deposits of the quaternary stratum. The glacial sediments are highly irregular in their horizontal and vertical distributions and also vary widely in their composition, which consists of sands, gravel and boulder clays.Simplified geotechnical profiles for the City of Berlinconsist of sandy tills interrupted by discontinuous layers of silt and marl. On the base of the marl one can find stones and boulders. In a greater depth of about 40 till 50 m below ground surface there is an organic brown coal layer of high density and low permeability. The groundwater level is 2 till 3 m below the ground surface and the permeability of the sandy soils is in the order of 10-3 till 10-4 m/s [1].

2.2

Wall-slab construction methods Besides shield-driven tunnelling and caisson constructions the main method of groundwater protecting construction used in Berlin is the cut-and-cover solution, also

34

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called wall-slab or trough-type construction.

It is build with almost impermeable vertical walls as well as horizontal base slab. Possible combinations of such wall-slab constructions are shown in Figure 1. Main difference between the combinations is the design depth of the slab. Figure 1b and 1c show top-seated slabs whereas Figure 1a and 1d represent deep-seated slabs. Top-seated slabs require either heavy weight of the slab or anchorage to prevent uplifting of wall-slab pit. The design depth of deep-seated slabs is calculated from the proof against uplift of the wall-slab construction. As an approximation to become an idea about the dimension of the construction one can have for a 15 m depth of the excavation below ground water level, about 15 m length for the anchor piles or a 30 m deep wall below groundwater level. In both cases the base slab is about 1.5 m thick.

The main components of all these constructions are: (i) walls including tie backs, (ii) slabs, and (iii) uplift anchor piles if required. The components are explained in the following subsections.

2.2.1 Wall construction methods including tie backs Very stiff and impermeable walls are required to support deep excavations in urban areas with very limited lateral wall deformations. In general diaphragm walls as well as secant bored pile walls are suitable solutions. In the majority of projects diaphragm walls are used. The thickness varies according to the design loads and boundary conditions between about 80 till 160 cm. Most projects are using solider pile walls (Berlin type walls) above the groundwater table to enable removal of that part of the wall at the end of construction.

In the cases with deep-seated slabs(Figure 1a and 1d) the vertical walls have to be built much longer than in the variant with topseated slabs and they have to reach till the depth of the slab to ensure a trough-type construction. Such very long walls lead to a The Bridge and Structural Engineer

high demand for the verticality of the wall until the final depth to ensure a closed joint between the diaphragm wall panels.

Tie backs are used instead of braces to support the excavation walls above the excavation level. Only one layer of tie backs is used in the case of a top-seated slab (Figs.

1c and 1b) due to the high groundwater level a few meters below ground surface. That enables installation of the tie backs above the ground water table. Trough excavations with deep-seated slabs (Figure 1a and 1d) require in most cases also additional layer of tie backs which have to be installed against the acting water pressure behind the wall.

marl as well as the brown coal layer have been used in several cases as natural horizontal impermeable layer for deep excavations. In these cases the site investigation has to be done very detailed especially in the depth of the natural impermeable soil layer to proof their homogeneity.

The two distinguished categories with artificial slabs shown in Figure 1 with topseated or deep-seated slabs have to be used if a natural slab is not available in situ. In the first variant the top-seated base slab is built as an underwater concrete slab (Figs.

1b and 1c). Depending on the acting water pressure the weight of the concrete slab might be enough to fulfil the proof of uplift of the excavation pit. If the water pressure is high below the slab then an anchoring of the slab before pouring is necessary to avoid uplift.

In the second variant the deep-seated slab is constructed as an injection or hydrojet grouting layer (Fig. 1d). The soil weight above the slab prevents uplifting due to the depth of the slab below the excavation level.

2.2.3 Uplift anchor piles

Fig. 1: Wall-slab construction methods in soils with high permeability as well as ground water table

The length of the tie-backs of the diaphragm walls varies from 15 till 70 m with maximum anchor forces of about 1,500 kN. Each anchor comprises a circ of 9 strands that is embedded into the grouted portion. Most of the anchors are temporary and some of them were removed later.

2.2.2 Slab construction methods The most cost-effective slab construction is a natural nearly impermeable soil layer. The The Bridge and Structural Engineer

Two different types of anchor piles are preferably to be used for top-seated slabs.

The mostly used RI-Pile consists of aHsection steel profile that is vibrated into the soil (Fig. 2, middle and right). At the pile tip there is an expansion made by steel bars welded on the pile shaft (Fig. 2, Photo at the bottom, middle). Two injection pipes are attached to the steel profile in its inner corners (cf. same Photo as before, one pipe is visible). During the vibration of the pile into the ground the water saturated soil in the vicinity of the pile liquefies and the continuously through the pipes injected mortar mixes with the liquefied soil and produces an earthen concrete shaft.

Excavated RI-Piles proved a thickness of that earthen concrete of about 15 cm resulting in an overall RI-Pile diameter of about 59 cm, back calculated from the injected volume of Vol. 48 | Number 4 | December, 2018

35

Fig. 2: Anchor piles for concrete base slabs: GEWI-Pile (left) and RI-Pile, head (top middle) and tip (bottom middle), excavated RI-Pile after load testing (right)

mortar [4]. Attached to the pile head there is a steel plate which has to be embedded in the concrete slab. As an alternative bored piles of small diameter the so called GEWIPiles can be used (Fig. 2, left). The bore hole is grouted with cement mortar after placement of the steel bar.

The experience with large and deep excavation in sandy soils with high groundwater level and anchorage against uplifting was very limited in the 1990s.

Therefore extensive tension loading tests were performed on single piles as well as groups of piles before the construction of the excavations to determine the load capacity of the slab anchor piles of Fig. 1c [4]. A total number of 21 single RI-Piles and 7 GEWIPiles with a length between 9 and 24 m have been tested at six different places.

Furthermore two groups of 5 RI-Piles, two groups of 9 RI-Piles and one group of 5 GEWI-Piles were tested at five different places on the VZB-Project site.The slab anchor piles have been placed with a distance of about 3 by 3 m.The single pile tests were performed with force control whereas the 36

Vol. 48 | Number 4 | December, 2018

pile group tests were done displacement controlled to simulate the existence of the underwater concrete base slab which prescribes nearly the same displacement to every anchor pile.

The load-heaving data from the single pile loading tests resulted with broad variation especially due to the different soil densities at the sites and the different effective pile diameters. A normalization of the measured pile head heaving and the tension force as well, both normalized to the pile length, made the results comparable [4].

Using this procedure Fig. 3 shows the evaluated load-heaving results for all piles longer than 15 m. Two mean curves can be approximated as shown, one for each kind of pile - GEWI and RI respectively.

At the same level of tension force per pile length the GEWI-Piles clearly behave much softer compared to the RI-Piles, because of the smaller cross section of the tension effective steel. For piles shorter than 15 m no mean curve can be found, caused by the upper inhomogeneous soil layers. Also one

The Bridge and Structural Engineer

Fig. 3: Normalized load-heaving curves for GEWI- and RI-Piles with pile length L > 15 m [4]

test with a RI-Pile longer than 15 m does not fit the mean curve which is caused by the soil conditions too (Fig. 3).

The Quality Assurance required that after the installation of the anchor piles (Fig. 4), three percent of them had to be tested in situ, which has to be performed again from a

pontoon. Afterwards the final concrete base slab has been poured underwater with the aid of divers ensuring the correct embedment of the pile heads.

3.

Numerical simulations

Numerical simulations by the finite element method are performed mainly to predict the wall and slab displacements. Calculations using simple elasto-plastic soil models predicted maximum base slab heaving of about 41 mm after dewatering which underestimated the measured values.The underestimation was mainly caused by the fact that the softening of the soil due to the excavation and pile driving was not concerned in the simplified numerical analysis [1]. Such differences between predicted and measured deformations were obvious also for the diaphragm walls.

Simulations using a more sophisticated soil model lead to much better matching predictions of deformations [5, 6].

Fig. 5 illustrates the measured diaphragm wall displacements by means of vertical inclinometers inside the walls. Measurements were done after the following construction stages: first prestressing of the installed tie backs, complete underwater excavation of the pit M1, vibratory installation of the RI-Piles, and second prestressing of the tie Fig. 4: Vibratory installation of a RI-Pile from a backs. Other measurements of the same excavation pontoon to prevent uplifting of the afterwards poured underwater concrete slab in a trough type excavation M1 have been used in [5, 6] for comparison.

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

37

realistic predictions of soil-structure interaction phenomena incorporating large deformation which cannot be simulated using classical lagrangian finite element schemes.

4.

Fig. 5: Measured wall displacements by vertical inclinometer for different construction stages of the excavation M1 (MQ 1)

Vibration of RI-Piles doubles the wall deflections after the excavation stage and results in up to almost 8 cm displacement as a maximum (Fig. 5).

Such large deformations have not been predicted and partial overloading e.g. of tie backs had to be taken into account. There were no suitable numerical models capable to realistically predict the installation effects of vibratory driven RI-Piles.

A short overview of similar experiences from measurements with deep excavations in Berlin is given in [7]. Different construction procedures and geotechnical installation methods are described and discussed, all of them leading to unpredicted large deformation of the geotechnical structures and the surrounding ground.It is concluded that there are existing only a few methods capable to realistically predict the measured deformations.

Own recent extensive research work also focuses on such installation effects with geotechnical structures such as piles [8, 9]. The numerical method used in these simulations is the so called Arbitrary Lagrangian Eulerian (ALE) approach.

That is a generalized finite element framework to consider large deformations and material flow through the mesh. By means of the incorporation of sophisticated soil models one gets much more 38

Vol. 48 | Number 4 | December, 2018

Monitoring and data management

Quality assurance is an important issue of any huge geotechnical engineering project and with deep excavations it shall include an extensive monitoring system to ensure the quality of the constructions and to control and proof the design and predictive calculations. The impact of a project such as the VZB project on the urban life and on the environment wouldn‘t be minimized without a sophisticated project monitoring as well as data management. Based on the experience with numerous large trough excavation projects the data requirements for a web-based monitoring and data management platform has been assembled (Fig. 6 and Fig. 7).

A new web-based software DoMaMoS has been developed recently to cover all the needs in a new manner and to provide the practitioners a tool for efficient geotechnical monitoring and data management for their daily work as well as for disaster prevention [10]. During execution works most of the participants provide and use data which is more or less relevant for any decision process.

Among these data only the key information, i.e. construction objects, basic geometries,

Fig. 6: Participants and geotechnical requirements with deep excavation projects [10] The Bridge and Structural Engineer

and right place. Therefore a web-based software platform is suitable and necessary to support such complex geotechnical projects with numerous sources of big data.

References

Fig. 7: Web-based software DoMaMoS covering geotechnical data and project requirements [10].

1.

Savidis S., and Rackwitz F., “Development of Transport Infrastructure under the City of Berlin”, The Bridge and Structural Engineer, ING-IABSE, New Delhi, Vol. 36, No. 3, 2006, pp. I.47-I.56.

2.

Mönnich K.-D., and Erdmann J., “Planning New Public Transportation in Berlin”, Structural Engrg. Intern.,Vol. 7, No. 4, 1997, pp. 231232.https://doi.org/10.2749/ 101686697780494437

3.

Mönnich K.-D., Scherbeck R., Klapperich H., Savidis S., and Effenberger K.,”Geotechnical, applied geological and environmental aspects during conception, planning and ongoing realization of the mega-project ‘Berlin City Traffic’-Infrastructure”, In: Marinos, Koukis, Tsiambaos& Stournaras (eds.),Proc. Intern.

Symp. On Engrg. Geology and the Environment.

Athens, Greece, 23-27 June 1997, Balkema, Rotterdam, pp. 2803-2808.

4.

Rackwitz, F., “Numerical Analysis of Anchor Piles for Deep Excavations”, Proc. IABSE Symposium Metropolitan Habitats and Infrastructure, Shanghai, China, 22.-24.

September 2004, Report with CD-ROM, Paper SHA338, 6 pp.

5.

Nikolinakou M.A., Whittle A.J., SAVIDIS S., and Schran U., “Prediction and Interpretation of the Performance of a Deep Excavation in Berlin Sand”, Journal of Geotechnical and Geoenvironmental Engineering, Vol. 137, No. 11, 2011, pp 1047-1061, https://doi.org/ 10.1061/(ASCE) GT.1943-5606.0000518

6.

Nawir H., Prasetyo B.E., and Apoji D., “Excavation Analysis using Stress Path Dependent Soil Parameters”, Proc. Regional Conference in Civil Engineering (RCCE) and The Third International Conference on Civil Engineering Research (ICCER), August 1st-2nd 2017, Surabaya – Indonesia, 2017, pp. 115-120.

7.

Hettler A. and Triantafyllidis TH., “Deformations of Deep Excavation Walls

measurement devices, measured data, is most important for disaster prevention. Fig. 6 shows some of that key information of a deep excavation project.

Fig. 7 illustrates the general sources of data, objects and documents which have to be managed in geotechnical engineering projects. Data are unequally distributed amongst the participants of the project. Therefore it is one main task of the project management to control the flow of information between all involved people in a project. The outer circular ring in Fig. 7 contains requirements from project management to achieve a safe and economic geotechnical construction.

5.

Conclusions

The existing geotechnical and hydrogeological conditions in the City of Berlin, i.e. mainly sandy soils with high permeability in conjunction with a groundwater table just about 2 till 3 m below ground surface, as well as the necessity to save the environment in the vicinity lead to mainly deep trough-type excavations. Sophisticated numerical simulations are required to model the resulting soilstructure interaction realistically. Monitoring and data management are the keys of geotechnical project and risk management as well as disaster prevention providing right information at right time The Bridge and Structural Engineer

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induced by Construction Processes”, Proc. of the 17th International Conference on Soil Mechanics and Geotechnical Engineering, 2009, pp. 2457-2460, https://doi.org/10.3233/ 978-1-60750-031-5-2457 8.

40

Aubram D., Savidis S., and Rackwitz F., “Theory and Numerical Modeling of Geomechanical Multi-material Flow” In: Holistic Simulation of Geotechnical Installation Processes. Benchmarks and Simulations.

Triantafyllidis, Th. (Ed.), Lecture Notes in Applied and Computational Mechanics, Vol. 80, Springer Verlag, 2016, pp. 187-229. https:// doi.org/10.1007/978-3-319-23159-4_10

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9.

Aubram D., Rackwitz F., Wriggers, P., and Savidis S., “An ALE method for penetration into sand utilizing optimization-based mesh motion”, Computers and Geotechnics, Vol. 65, No.4, Elsevier, 2015, pp. 241-249, https://doi.org/10.1016/j.compgeo.2014.12.012

10. Rackwitz F., Savidis S., and Rickriem J., “Webbased Data and Monitoring Platform for Complex Geotechnical Engineering Projects” Journal Geotechnical and Geological Engineering, Vol.31, No.3, Springer, 2013, pp.

927-939, https://doi.org/10.1007/s10706-0129592-4.

The Bridge and Structural Engineer

FIRST TUNNELS ACROSS MAJOR RIVER HOOGHLY FOR EAST WEST METRO IN KOLKATA

Biswanath DEWANJEE Chief Engineer Kolkata Metro Rail Corporation Limited biswanath_dewanjee@hotmail.com In-charge of execution of underground corridor of Kolkata East-West Metro Project. A post-graduate Civil Engineer, FIE& Life member of tunnelling Association of India with more than 27 years of experience in infrastructure industry in highways, bridges, township infrastructure and Metro Railway.

Summary Kolkata East-West Metro Project is an important urban engineering project of the region involving numerous challenges including crossing of river Ganges. Twin tunnels of Kolkata East West Metro Corridor passes below the river Ganges with 520m of river crossing width at a depth of approximately 13m below river bed. The 5.55m internal diameter tunnels with RCC segmental liner has been constructed using earth pressure balancing tunnel boring machines. This is the first transportation tunnel project in India under any major river. This ambitious engineering challenge involved meticulous planning of the alignment and geotechnical investigation. The approach adopted for design of this underground tunnel as well as face pressure calculation and grouting protocol are highlighted in this article. The precautionary measures and safety arrangements are also discussed.

Keywords: Kolkata East West Metro, tunnel alignment, tunnel design, face pressure, tunnel waterproofing.

1.

Introduction

As per UN Habitat report, global urban population has increased from in year 220 million in year 1900 The Bridge and Structural Engineer

to 3200 million in year 2005. Such fast urbanizing demands futuristic design of cities to accommodate mega population while creating high quality of urban life. Tunnels provide an effective transportation corridor below earth surface with minimal impact to busy city life at surface level.

The advent of Urban Rail projects in last century have changed the dimension of travel in densely crowded cities and success of such metro projects largely depend on effective tunnelling in busy districts of the cities. The 1st Metro line in Kolkata was initiated in 1972 and commissioned in 1984 in North-South direction which was eventually the 1st rapid transit system in India and presently carries about 0.6 million passengers per day. Kolkata Metropolitan Area is a fast developing megacity with expanse of urban conglomeration around the core part and houses 16 million people.

Providing transportation solution in this 300 year old metropolis is a daunting task for city planners.

Several Metro corridors are planned in this city and sub-urban region with total length of 106 Km of new lines. A very challenging Metro corridor is being implemented in East-West direction with 16.6 Km corridor length and project cost of around INR 9000 Crs. 65% of this metro corridor runs underground through densely populated and built up part of the city and it crosses river Ganges Vol. 48 | Number 4 | December, 2018

41

after award of design & build contract. It was necessary to plug the boreholes with cement slurry during withdrawal of casing pipe to avoid river water infiltration in lower strata through impervious capping layers in top which could be detrimental for tunnelling.

through tunnelling. In this present case study of passage of underground tunnels below river Ganges, the challenges associated with design and construction of such unprecedented underground project undertaken in juvenile alluvial geology of Ganga-Brahmaputra deltaic region is demonstrated.

2.

Engineering characteristics of sub-soil in tunneling horizon is shown in Table 1 :

Tunnelling scheme across river Hooghly

2.2 Finalisation of alignment

2.1 Geotechnical investigation Boreholes for geotechnical investigation in river portion has been carried out by marine cable percussion method using floating raft/ boat. Investigations were done in project planning stage as well as in execution stage

2.2.1 Horizontal Alignment of Tunnel Below River Ganges The horizontal alignment for river crossing has been selected with following considerations :

Table 1 : Engineering Characteristics of Sub-Soil Soil Strata & Nature

Unit 1 Made Ground

Depth

Tunnel Section

5.5m All MSL to 4.5m MSL

Unit 2 4.5m All Organic MSL to Clay -10m MSL

Unit 3a Firm to stiff clay -10m Silt MSL to -40m MSL

Unit N Poisson’s Angle of Cohesion υ ) Friction (c’) Weight Value Ratio (υ Φ ’) (y) (Φ

Undrained Shear Strength (Cu)

Drained Young’s Modulus (E’)

Undrained Young’s Modulus (Eu)

kN/m³

17.5

19

East Side of River Unit 3b Sandy Silt / Silty Sand

kPa

kPa

MPa

MPa

28°

0

n/a

12

n/a

West- 0.25 side: 4-18 East side: 2-7

25°

5

25

6

8

12-40

30°

(z+7.2222) -0.1111

(z+4.706)0.353

25-31

32° (below – 24m MSL)

(z+7.8814) - 0.0847

(z+6.875) -0.3125

(z+7.549) - 0.098

(z+1.4286) - 0.4286

n/a

(z+4.706) -0.353

19

West Side of river River Section

Deg 0.3

12-27 0.2

West Side of river River Section East Side of river

0

1.25x E’

30°

19

10-42 0.2

16-57

32° (below – 24m MSL)

0

(z+6.875) -0.3125 (z+1.4286) -0.4286

n/a

z = Depth in meter from MSL

42

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

a)

b)

c)

d)

e)

2.2.2

Tunneling zone below the river is considered mostly in favorable tunneling zone of firm to stiff clayey silt with N Value 25 to 30 and angle of internal friction [Φ’ ] of 320.

The river in Kolkata had been used for water transport for centuries and it was ensured from Port Authority that bottom of jetty piles and shore line structures extends upto -20.3 m MSL and the crown of the tunnel must be sufficiently below that level so that it does not infringe any existing or abandoned structure.

In Urban underground projects in brownfield situation like Kolkata Metropolis, availability of land is always a challenge. The aspect of acquisition of land & constructability of Howrah Station at west bank of the river & intermediate Ventilation Shaft in east bank were major factors in finalization of alignment. Comparatively vacant areas were selected in both banks and alignment of the tunnel in the river section has been guided accordingly.

The proposed tunnels are at about 320 m away from existing Howrah Bridge which is a major entranceto the city & it is analyzed that tunnelling work at such distance has no direct effect on Howrah Bridge.

For easy maneuvering of Tunnel Boring Machines inside the river no horizontal curve is provided.

Vertical Alignment of Tunnel Below River

Hydrological data : This is a tidal river near estuary with progressive type of tidal wave

ranging from 3m to 4m with bore tides which is characterized by standing wave of about 1.75m high. As per reports available from Kolkata Port Authority, the highest scouring at location of the tunnel during year 1988 to 2003 was in the order of 4.5m while the highest silting was in the order of 6.5m & maximum water velocity was in the order of 2.5m/sec.

As revealed in survey conducted in February, 2004, maximum water depth of 17m was observed at 90 meters from right bank [Howrah side]. The gradient of the river was very flat [almost nil]. The deepest scoured river bed at the alignment of the tunnel as per report of Kolkata Port Trust was stated to be 23.865m below MSL. Before preparation of Detailed Project Report, an initial feasibility study for this river tunneling was done by Japan External Trade Organization [JETRO] and The lowest rail level suggested was – 28.74 m below MSL. Further bathymetric survey was conducted in DPR Stage in 2006 as well as after award of construction contract in 2010 and some changes in the river bed profile was observed as shown in Fig. 1. As per the latest survey, there is tendency of silting in right bank and deep channel is shifting towards left bank [Kolkata Side] with maximum depth 14.434m at 280 m from left bank.

2.2.3 Checking against Flotation & Heaving A relatively shallow tunnelsshould be checked against flotation due to differential water pressure with overall safety factor R / U > 1.2

Fig. 1 : River Bed of Hooghly – Bathymetric Survey

The Bridge and Structural Engineer

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43

Table 2 : Comparative Factor of Safety with different values of soil cushion Soil Cover [m]

Factor of Safety

Soil Cover [m]

Factor of Safety

12.4 10 8

3.50 2.86 2.32

6 5 4

1.787 1.518 1.25

Other factors influencing finalization of alignment are : o Schedule of dimension of the project [permissive horizontal and vertical curve for the transportation or utility medium], o Maximum grade requirements for the TBM, o Future channel improvements like dredging.

Fig. 2 : Schematic Diagram for Floatation Check

where: R is restraining force calculated by weight and shear resistance of soil & U is net uplift force considering weight of tunnel.

Where applicable for relatively shallow tunnels in clay, checking for heave due to shear failure of the ground at tunnel invert level (for example, for mining operations) will be undertaken following the method derived from the base heave analysis after Bjerrum & Eide (1956) Where: Overall safety factor: > 1.0 when surcharge is applied > 1.2 when surcharge is not considered Factor of safety for different soil covers at the river location are calculated and shown in Table 2.Tunnel vertical alignment is finalized with 3% vertical grade [permissible limit] on the basis of bathymetrical survey done in 2010 and critical cushion against maximum scour of 4.5m reported by Kolkata Port Trust is [15.855-4.5] m = 11.355 m which provides adequate factor of safety as per Table 2. The cushion provided is also required to be checked against blow out criteria during application of face pressure during tunneling which is detailed in section 4.2.

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Penetration from ship’s anchors in navigational waterway is also a guiding factor for soil cushion for tunnel in soft sub-soil condition like Kolkata.

Fortunately the riverine port of Kolkata is located on sea side of the tunnel alignment and there is no ship route in tunneling zone. However there is inland transportation in the river for both ferry passenger and cargo using motor launches, steamers and barges. Information regarding the project has therefore been transferred to the Port Authority and it is ensured that there will be no effect due to anchor penetration. The tunnel alignment below the River Hooghly has been shown in Fig. 3.

Width of River Crossing : 520 meters, Internal diameter of the tunnels : 5.55 m Spacing between tunnels : 16.1 meters Center to Center Depth of Tunnel : 16 m water depth plus depth of tunnel crown extra dose 13 m below river bed Maximum Tunnel Gradient : 3% [Approx.] & nature of Soil : Predominantly Stiff Clayey Silt in tunneling horizon.

3.

Structural Design of Tunnel lining

3.1 Basic circular tunnel structure The circular tunnel of 5.55m internal diameter consists of pre-cast concrete segmental lining which forms the permanent support of the tunnel and is installed inside the shield of the Tunnel Boring Machine (TBM), as the tunnel The Bridge and Structural Engineer

Fig. 3 : Tunnel alignment below river vis-à-vis geotechnical profile

excavation progresses. The TBM boring diameter is larger than the lining outer diameter. The void between the ground and the tunnel lining is continuously filled with grout from the shield tail. The segment lining consists of five large segments plus one key segment for each ring. The lining thickness is designed as 275mm and same universal segments will be used for all rings. The segments are bolted together during erection inside the tunnel shield, with bolts on the circumferential joint of each ring edge and bolts on the radial joints of each ring. The bored tunnel waterproofing is provided by a hydrophilic seal and EPDM (Ethylene Propylene Diane Monomer) gasket on the segment circumferential joints. The hoop load induced into the bored tunnel as a result of the ground water pressure and soil loads will be sufficient to compress the gaskets to prevent groundwater intrusion in combination with the hydrophilic swelling properties.

Gaskets on the circumferential joints will be compressed by the TBM jacking pressure and locked by the bolts connecting segments.

The Bridge and Structural Engineer

3.2

Design Approach

3.2.1 Static Lining Force The continuum analysis for ground and ground water forces is done using closed form analysis model developed by Duddeck & Erdmann (1982). This is based on a general plane frame analysis that will be carried out for varying soil stiffness and differential hydrostatic load. A full bond between the lining and the subsoil is assumed. Calculations has been carried out for the average effective unit weight (γav) of soil, considering the soil layers and groundwater table. The effect of differential hydrostatic pressure along the circumference of the tunnel has been considered in the analysis. The analysis is carried out at 20m intervals along the tunnel alignment.

Following critical sections are identified for detailed numerical analysis with the consideration of seismic loading.

• •

Ch -0+815 – Section near Howrah Maidan Station, shallowest section.

CH -0+620 – Section near Howrah Maidan Station, near shallowest section.

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45

• • • •

CH 0+620 – Section of tunnel crossing the Hooghly River with minimum soil cover.

CH 0+860 – Section near ventilation shaft, deepest tunnel.

CH 1+920 – Section beneath G+10 Govind Bhavan building CH 2+200 – Section of minimum tunnel spacing (9m centre to centre spacing)

3.2.2 Numerical Soil-Structure Interaction Analysis For specific critical locations identified through static analysis, more appropriate numerical soil-structure interaction analysis is done through numerical models.

Numerical analysis has been undertaken using PLAXIS version 9. A volume loss of 1.5% is assumed for the PLAXIS analysis.

This is conservative compared to typical values for earth pressure balance tunnelling with tail-skin grouting in soft clay.

Numerical analysis is undertaken with following construction sequence : o Initialize stress condition and water pressure; o Apply surcharge; o Excavate tunnel and install lining for 1st tunnel o Excavate tunnel and install lining for 2nd tunnel o Consolidation after construction completed o Change the properties of lining to long term modulus; o Apply seismic acceleration; and o Consolidation after seismic acceleration.

Relaxation of ground stress is assumed before installation of lining 3.2.3 Analysis of the effects of Imposed Distortion The maximum allowable deflection of the tunnel lining is 25mm on radius of the tunnel.

The induced bending moment by applying this distortion is derived by using the method of Morgan for jointed lining cases with reduction of lining moment of inertia based on the recommendation by Muir Wood . The predicted bending moment coupled with minimum thrust force will be input for reinforcement calculation.

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3.2.4 Seismic Lining Forces Kolkata is in seismic Zone 3 as per IS-1893: 2002, giving a Zone Factor, Z = 0.16g, corresponding to the Maximum Considered Earthquake (MCE). According to IS-1893: 2002, the design methodology adopted will ensure that the structures will possess at least a minimum strength to withstand a DBE event “without significant structural damage” and an MCE event “without collapse”. The design of tunnels to resist seismic loads is not explicitly covered by the Indian Standards; hence reference is made to internationally recognised design methods from published literature. In accordance with IS-1893:2002, the horizontal seismic accelerations corresponding to the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) are 0.16g and 0.08g respectively. The “Free-field racking deformation” method as elaborated in Hashash et al (2001) has been adopted for the design. The method assumes the structure will be racked by the soil surrounding it during an earthquake, with the degree of racking dependent upon the relative shear stiffness of the structure to the soil mass it replaces, and the free-field soil deformation profile.

The free field deformation of the soil during a seismic event is derived using the SHAKE 2000 software. The design inputs include ground motions obtained from the SHAKE 2000 software library and from available ground motion libraries like Chamoli (1999), Diphu (1988) and Burma (1995) events. The input data includes soil profile, ground acceleration due to 0.08g (DBE) and 0.16g (MCE) and dynamic shear modulus derived from the ground investigation.

3.2.5 Other factors affecting design of tunnel liners o Analysis of the Effects of Poor Ring Build o Design of Radial Joints o Analysis of the Effects of Jacking For Propulsion at the Circumferential Joint o Effects of Uneven Shield Shoving Loads o Grouting Loads o Analysis of the Handling and Stacking The Bridge and Structural Engineer

o Face Pressure to be maintained during advancement - Mean Values determined at 20m interval along the alignment by COB Method [Dutch Center Ondergroun Bowen] o Face Pressure during Stoppages - Mean of values determined at 20m interval along the alignment by Max Ground Water Load plus 20 Kpa

The lining stiffness is reduced according to Muir Wood (1975) to account for the effect of radial joints. This is based on the number of joints for each ring and the reduction of lining thickness at joints: Ir =Ij + (4/n)2 x I where, Ij is the moment of inertia at joint, I is the moment of inertia through the nominal lining thickness: and n is the number of segments for each ring

The mean values are further stepped in 40 m interval and mean graph is generated with upper envelop of Maximum Face pressure of 0.2 bar more and lower envelop of Minimum Face pressure of 0.2 bar less than mean value. Though stoppages during river crossing is not at all recommended, in case it is required for more than 24 hours during break down and weekends, the chamber is recommended to be kept pressed by injecting Bentonite. The face pressure graphs thus generated are cut off to a maximum value of 3.6 bar considering maximum rated face pressure of the machine of 4.5 bar. A typical face pressure plotting for advancement is shown in Fig. 5.

Based on the out puts, the design bending moments are compared in Fig. 4 in between different sections and it is found that RCC design is most critical river and shallow sections.

Fig. 4: Comparison of Design Bending Moment for tunnel liners

4.

Maintenance of face pressure during tunnelling

4.1

Aspects of face pressures & application for tunnelling below river Ganges Computation of tunnel face pressure during advance as well as during stoppage are extremely important and maintaining the parameters of face pressure during tunneling is equally important in open water to have an effective control. Unlike normal circumstances, maintenance of machines under the river as well as interventions are expensive and involves higher risk factors.

Face pressures are computed using values of overburden and ground water parameters along the tunnel alignment at tunnel depth using following principles :

The Bridge and Structural Engineer

Fig. 5: Typical Face Pressure during Tunneling

4.2

Blow Out Verification The riverine portion of the tunnel is most vulnerable against the blow out phenomenon due to application of the face pressure as the resisting force R in Fig. 8 should have adequate factor of safety against uplift blow out pressure U provided by face pressure.

This aspect has been appropriately verified before finalization of the tunneling scheme.

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47

4.3

Comparison of theoretical and actual face pressures Tunneling below river Hooghly has been done with meticulous control over the parameters. A 24X7 team of supervision personnel was formed to monitor the matters and a protocol for high level management information system was developed.

During excavation by EPB Machine, the volume of the extracted material should be equal to the volume of the excavated material. In order to achieve this equilibrium, apart from maintaining a proper working pressure, it is necessary to control other fundamental parameters, like apparent density and the conditioning system of the material in the chamber. All these aspects are also strictly related to settlement control.

Furthermore, a crucial parameter in the settlement control is represented by a proper grout injection of the annular gap as well as an adequate filling of the void related to the shield conicity.

Fig. 6: Schematic Diagram for Blow Out

The maximum pressure against blow out is represented by following equation:

[

Pmax = C. γ +

2c+C.k .γ`.tan φ

h ________________________

D

]

Where ‘C’ is soil cover to tunnel crown in meter, ‘c’ is cohesion in Kpa, ‘K h’ is horizontal earth pressure coefficient, ‘γ’ & ‘γ’ are unit weight & Effective unit weight of Soil in KN/ cum and ‘Φ’ is angle of shear resistance of soil in degree

The density in the chamber shall be kept as high as possible. The value of the density of the material into the working chamber should never be lower than 12.0 KN/M3 . It would be desirable to keep a value of 14 KN/M3 or higher in order to have the closest pressure gradient between the soil at the front and the conditioned material in the chamber.

The maximum pressure against blow out is plotted against face pressure in Fig. 7 and it is seen that the tunnel is most critical against blow out in river section and the soil cushion provided is justified.

Tunneling was smooth below the river with no major surprises, all the protocols mentioned were strictly followed and a uniform rate of progress was achieved. The tunneling below the river was started on 14th April, 2017 and both the tunnels crossed the river stretch in 66 days. Following figures depict the status of tunneling parameters during crossing of the river.

5.

Fig. 7: Pressure against Blow Out vs Tunnel Face Pressure

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Vol. 48 | Number 4 | December, 2018

Conclusion

Tunneling in urban situation demands meticulous planning, investigation and design considering all the factors in the tunneling horizon. In this article it is depicted how analysis of necessary data

The Bridge and Structural Engineer

Fig. 8: Comparison of Theoretical and Actual Face Pressure

collected through geotechnical investigation has helped in tunnel planning and design below river Ganges . Analysis of hydrological data is also an extremely important factor for consideration of a tunnel prospect in open water which is described in the article. It is needless to mention that strict adherence to tunneling parameters and maintenance of flawless emergency protocol is mandatory for the success of a tunnel below river.

The success of first transportation tunnel below any mighty river in India will definitely inspire similar achievements in the country in coming years.

the project was initiated under the leadership of Dr. B.C. Roy, Ex- Joint Project Director of General Consultants, whose contribution is hereby acknowledged.

6. Acknowledgement The effort by KMRC Management to take up the challenging job in Kolkata and the untiring endeavour of all fellow designers and engineers from Consultants and Contractors demand acknowledgement. The design basis report and subsequent analysis for the underground section of The Bridge and Structural Engineer

References 1.

Bjerrum L. and Eide O. (1956): “Stability of strutted excavations in clay”. Geotechnique 6.

2.

Duddeck H. and Erdmann J. (1982): “Structural design models for tunnels”. Proceedings of Conference Tunnelling ’82, pp 83-91, UK.

3.

Hashash, M.A., Hook, J.J., Schmidt, B. and Yao, J.I. (2001): “Seismic design and analysis of underground structures”. Tunnelling and Underground Space Technology Vol. 16 p 247-293.

4.

Muir Wood, A.M. (1975). “The circular tunnel in elastic ground”. Geotechnique 25, No. 1, 115 – 127.

Vol. 48 | Number 4 | December, 2018

49

DESIGN AND CONSTRUCTION ASPECTS OF ÜSKÜDAR STATION IN ÜSKÜDAR-ÇEKMEKÖY METRO LINE (UCM) IN ISTANBUL

Emre DUMAN

Baris Özcan

C. Utkan Çorbacio ğ lu

Lead Design Manager SYSTRA Mumbai, Maharashtra, India eduman@systra.com

Director Do ğ us Construction Teknik Engineering Istanbul, Turkey barisoz@dogusinsaat.com.tr

Engineering Manager Do ğ us Construction Teknik Engineering Istanbul, Turkey utkanc@dogusinsaat.com.tr

Emre Duman, born 1981, received his civil engineering degree from Istanbul Technical University

Baris Özcan, born 1981, received his civil engineering degree from Istanbul Technical University.

C. Utkan Çorbacio ğ lu, born 1982, received his civil engineering degree from Istanbul Technical University

Summary Üsküdar-Çekmeköy Metro Line, which is located on the Asian side of Istanbul, is an 18 km underground metro line consisting of 27 km TBM tunnel, 13 km NATM tunnel with 16 underground stations and having a daily capacity of 1.600.000 passengers. Both Marmaray and ÜsküdarÇekmeköy Lines have stations at Üsküdar which enables integration between European and Anatolian districts of Istanbul. A combination of construction techniques, termed as bottom-up and top-down methods is selected for construction of Üsküdar Metro Station, which has dimensions of 207m by 26m with a depth of 21m below the sea level. The station is seated between Marmaray Station and the existing buildings which was a relatively narrow corridor. In the east part of station, there are very close buildings and a heritage building which makes the excavation safety highly critical. In this part, a more reliable method for controlling the ground settlements, top-down construction method has been chosen. In the west part, buildings are relatively far therefore a bottomup method with some special details could be used.

Some structural elements of excavation support system are designed as a part of permanent final 50

Vol. 48 | Number 4 | December, 2018

lining which made it possible to increase the width of the permanent station structure which was necessary for passenger circulation. As being an important part of city transportation high level of seismic analysis was required. Site specific probabilistic earthquake hazard analysis and soil amplification effects have been considered in the seismic design of station structure. Calculated free field deformations have been modified considering rigidity of the station in order to obtain structural deformations and internal forces. Starting from early stages of basic design up to the site implementation of detailed design, engineering experience obtained from design and construction phases of this station has a rich engineering value and is an example for the near future rail projects which are being planned in the metropolitan cities to solve the transportations problems.

Keywords:cut-cover, top-down, bottom-up, metro station, construction method 1.

Üsküdar Çekmeköy Metro Line

Underground transportation needs of Istanbul are greater than ever. As the population of Istanbul grows very fast, there is also a radical increase in The Bridge and Structural Engineer

Fig.1: Alignment of UUC Metro Line

the ownership of individual cars in the last decade.

Increasing traffic urges new metro lines to be constructed in Istanbul. Üsküdar Çekmeköy Metro (UCM) line, which is located on the Asian side of Istanbul, is an 18 km underground metro line consisting of 27 km TBM tunnel, 13 km NATM tunnel with 16 underground stations. This westeast bound line is integrated to two existing and two future main transportation lines.

Construction started in 2012 and is completed in 2017 including E&M and architectural works.

Among those 16 stations, Üsküdar is a special type station due to its two different contrary construction methodology. Top-down and bottom-up methodologies have unique advantages and disadvantages in respect of physical and management-wise restraints.

2.

UCM – Üsküdar Station

Among those 16 stations, Üsküdar is a special type station due to its two different contrary construction methodology. Top-down and bottom-up methodologies have unique advantages and disadvantages in respect of physical and management-wise restraints.

2.1 General Aspects of Design Üsküdar Station is located west-east longitudinal direction, next and parallel to existing Marmaray Station which has -32m bottom of foundation elevation. TBM tunnels from the station towards the east direction are passing between buildings in the ground and the existing Marmaray TBM tunnels.

Fig.2: Location of Üsküdar Station The Bridge and Structural Engineer

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51

Despite heavy passenger circulation is expected, due to very limited construction area, a compact station is designed in architectural point of view. Passenger movement is handled with four entrances from the ground and three passages from Marmaray Station which are located in ticket hall level.

One floor below is mainly designed for technical volumes and the bottom level is for passenger platform.

In the west end of the station from ground to approximately level -15m general geology formation is marine deposits and silty sand layers. This highly weak soil is even going deeper towards the east end of the station where rock level is 8 m below the bottom of foundation consequently a soil improvement

is included in the design. Rock is generally moderately weathered clay-stone which is literally named Thracian Formation (Fig. 3).

In the east part of the station, many buildings including a historical building are very close to station excavation. Due to this reason, design development is continued according to a more settlement-controlled construction method called “top-down”. This choice of method also enabled an additional space for construction activities. West part is designed as conventional “bottom-up” with some modifications.

Excavation support system (ESS) design is inherently different for top-down and bottomup sections however secant piles are used for

Fig.3: Geological Profile

52

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The Bridge and Structural Engineer

Fig.4: Plan view showing risky buildings close to excavation and general secant pile system

both sections due to high ground water level which is just below the surface (Fig. 4). Shear keys are designed between secant pile wall and station structure almost for full perimeter so that the piles work as a tension member against stability problems caused by hydraulic uplift.

As Istanbul is close to a highly active seismic region it was important to determine seismic parameters carefully. Middle East Technical University (METU) prepared a probabilistic “Seismic Hazard Report for UUCM line” Akkar, 2013, considering both historical and recent earthquakes. Seismic parameters were estimated for a return period of 72, 475 and 2475 years return period. Every station’s distance to fault zone and soil amplifications due to local geological conditions were also considered to obtain the parameters. To determine the sectional forces two levels of ground motion has been considered; Operating Design Earthquake (ODE) with 50% of occurrence in 50 years and Maximum Design Earthquake (MDE) with 2% probability of occurrence in 50 years. In seismic analysis methods given in “Seismic Design of Tunnel, Wang, 1993” and “Seismic Design and Analysis of Underground Structures”, Hashash, 2001 have been implemented. The following calculation procedure has been used: i.

Shear wave velocity is determined based on the in-situ tests and shear strain level (Vs).

The Bridge and Structural Engineer

ii.

Peak ground velocity is determined based on Seismic Hazard Analysis also considering soil amplification. (PGV)

iii. Shear strain of soil is calculated. γsoil = PGV/Vs

Fig.5: Shear modulus of box structures

iv.

Shear modulus of the RC structure is calculated for 1 kN of unit load. Gstr = 1/γunitL.

v.

Shear strain of the structure is calculated. γstr = 2 (Gsoil/Gstr )/(1+Gsoil/Gstr ) γsoil .

Fig. 6: Simple frame analysis models Vol. 48 | Number 4 | December, 2018

53

vi.

Shear deformation of the structure is calculated which cannot exceed double of the free field deformations. Point loading or triangular loading selected depending on thestructural and geotechnical conditions. Δstr = γstrH

The method is based on the concept that it is unlikely that such structures, which are constrained by the surrounding medium (rock or soil), could move to any significant extent independently on the medium, or be subjected to vibration amplification. This approach focuses on the deformation aspect of the ground and the structures.

PGV values to corresponding shear wave velocities have been used as an input to shear strain calculations.

Table 1: Shear wave and peak ground velocities Soil Type

Vs (m/s)

MCE, PGV (cm/s)

Made Ground Alluvial Soil

180 200

68.4

Weathered Rock

500

53.2

Following above mentioned analysis deformations obtained different sections of the station is given in Table 1. R=1 for ODE, R=2 for MDE have been used in structural design load combination providing elastic behavior in ODE, and limited plastic behavior in MDE.

Table 2:Calculated deformations, Δs (cm) ODE

MDE

West Side

1.4

7.1

East Side

2.1

10.3

2.2 General Aspects of Construction Methodology Besides controlling the deformations, it was also aimed in top-down section to cast the slabs as soon as possible and reach to foundation elevation enabling TBM breakthrough in an earlier date. Space created after the completion of top slab was also used for construction operations. After completion of excavation support system piles, construction of top-down and bottom-up sections started independent from each other.

2.2.1 Top-Down Section Main concept of top-down methodology is based on carrying the loads of structural elements as construction goes deeper with king post piles and placed top slab over ESS piles. First excavation step is completed till the bottom of top slab. ESS piles are trimmed to form notch in order to place the top slab onto. Two rows of king post piles are constructed in the cross-sectional direction.

Also, plastic soil improvement piles are

Fig.7: Notch detail 54

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

Fig. 8: Rebar connection between two slab levels with couplers

Fig. 9: King post piles with steel gussets

constructed. Soil improvement under foundation is maintained by plastic piles and crushed stone barrier layer with a thickness of 120 cm between those piles.

Top slab supported by king post piles and ESS pile notches is cast with coupler connections

for outer wall vertical rebar. Following the second stage excavation, ticket hall level slab shall be casted connected to king post piles with steel gusset. Top slab and ticket hall slab shall be connected to each other with coupler connected rebar (Fig.9) therefore excavation can continue as the Ticket Hall slab is in suspension. According to circumstances outer walls can be cast or not since designers has considered both alternatives. This process continues similarly down to bottom of foundation. The whole load of slabs and side walls were carried out by KP piles and the notch.

As groundwater level is so high a continuous waterproofing system had to be implemented.

For such situation KP piles had to be cut off before completion of foundation concrete works. Foundation is cast leaving 2.5m*2.5m square opening for each king post pile. A steel structure is designed specifically for this operation which supports the slab with 4 bases on top for jacking during pile cut-off operation. Deformations are closely monitored by micrometers during suspension and cutting off piles which are generally around 2 to 4 mm. KP pile is cut with razor wire from two levels for pulling a slice.

Following the waterproofing works, rebar installed with welding to outer steel shell then concrete is poured and a closed frame structure has been achieved. Finally, KP piles

Fig. 10: Column suspension system The Bridge and Structural Engineer

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55

Fig.11: Construction sequence of bottom-up section

are covered with a non-structural reinforced concrete layer for corrosion protection.

2.2.2 Bottom-Up Section West part of the station is constructed by conventional bottom-up method. Secant piles are supported by four levels of steel pipe struts. However, a modification in the support system is required due to narrow construction space. Waling beams are designed as

permanent part of outer wall. To serve this purpose, waterproofing membrane is installed beforehand and waling beams are hanged to the vertical reinforcement of pile cancelling anchor connection with the piles. Rebar continuity is maintained with dowel rebar in the up direction and with coupler in down direction. With such application available space has been used more efficiently.

2.3 Discussions on Construction Methodologies Both methods used in this station include innovations and improvements on conventional bottom-up and top-down methods. Optimization of use of space, flexible construction planning and deformation control are the key features of developed methods. These developed construction methods can be useful tools for engineers who are willing to create a reliable structural system adapts on the existing site conditions and time schedule demands of such specific projects.

Construction started in 2012 and is planned to be completed in 2017 including E&M and architectural works. Among those 16 stations, ĂœskĂźdar is a special type station due to its two different contrary construction methodology. Topdown and bottom-up methodologies have unique advantages and disadvantages in respect of physical and management-wise restraints.

Fig.12: Notch detail 56

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The Bridge and Structural Engineer

References 1.

Akkar, S. (2013). Seismic Hazard Report for UUCM line.Report No: 2013-03-03-2-01-04 Middle East Technical University (METU), Ankara, Turkey.

2.

Wang, J. N., (1993). Seismic Design of Tunnels.

Parsons Brinckerhoff Inc., New York.

The Bridge and Structural Engineer

3.

Hashash, M. A., Hook, J. J. and Schmidt, B. (2001). Seismic design and analysis of underground structures. Tunnelling and Underground Space Technology, Vol. 16, pp.

247-293.

4.

Özmen, A., Çaliskan, F. (2016). Üsküdar Istasyonu Yapisal Tasarum Uygulama Projesi Raporu. Prota, Ankara, Turkey.

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LAUNCHING THE WORLD’S LARGEST TUNNEL BORING MACHINE

Peter THOMPSON Director of Infrastructure Director Arup Hong Kong peter-a.thompson@arup.com

Abstract Ground breaking in every sense, the Tuen Mun Chek Lap Kok Northern Connection Sub-sea tunnel project will complete the main arterial transport link between Hong Kong, Zhuhai and Macau with sections reaching depths of up to 60m below sea level. Incorporating the world’s largest diameter tunnel boring machine, the project presented a number of different challenges including a critical launch from the northern approach in Tuen Mun which was undertaken at a shallow depth in newly formed reclamation with barely more than a single tunnel diameter of cover. To facilitate the entry of this large tunnel boring machine into these challenging ground conditions an innovative launch shaft design was devised, made up of multiple cells that work together in hoop action to create an open excavation with minimal strutting which had the

Peter Thompson received his Civil Engineering Degree from Bristol University and a Master Degree in Soil Mechanics and Engineering Seismology from Imperial College UK. Area of Specialization: Geotechnical Engineering for Road, Rail, Metros, Airports, Ports, Buildings and Energy Infrastructure.

advantage of not only expediting the construction works programme but also to made it easier to maneuver and work on the tunnel boring machines once inside. This paper describes the evolution and development of this critical design structure for the project and its advantages in terms of constructability and programme.

1. Introduction The Tuen Mun-Chek Lap Kok Link Northern Connection Sub-Sea Tunnel is an essential design and build project connecting the Hong KongZhuhai-Macau Bridge Hong Kong Boundary Crossing Facility island, a newly reclaimed area adjacent to the Chek Lap Kok Airport, with the west side of the Hong Kong New Territories at Tuen Mun Area 40 as part of a strategic plan to create better connectivity across the Pearl river delta as shown in Fig. 1.

Fig. 1: Site Location Plan 58

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The Bridge and Structural Engineer

The project comprises the design and construction of a 4.2 km length of twin sub-sea tunnels beneath the Urmston Road channel which are connected at either end to cut and cover structures in both the northern and southern landfall areas which were formed within newly formed reclamations. The sub-sea tunnels, with an internal diameter of 12.4m, each contained a two-lane carriageway, requiring a tunnel excavation external diameter of 14m which at the time would be of record breaking size for the region.

However, as an innovation to the tender design, it was proposed to replace an approximately 500m length of cut and cover structure with the northern landfall reclamation area in Tuen Mun with bored tunnel through an extension of the sub-sea bored tunnel as illustrated in Fig. 2 below.

A challenge to the technically feasibility of this proposed innovation was that the northbound exit tunnel for the project was required to contain a third climbing lane which would require the internal diameter to be increased to 15.6m with a corresponding increase to the external diameter of 17.6m external diameter making it the largest tunnel ever constructed before in the world. Due to the large dimension of the bored tunnels and

shallow cover within freshly reclaimed areas, a similarly innovative solution was therefore needed to be developed for the associated launching shaft at the northern landfall to house such a large machine.

2. Ground Conditions The proposed temporary launch shaft is located within the new reclamation area constructed to form the Northern Landfall for the project, in the south-east waters of the existing water frontage of the River Trade Terminal (RTT) and Chu Kong Warehouse in Lung Mun Road, Tuen Mun. The existing seabed level at the location of launch shaft varies between approximately -10mPD and 13mPD and the ground level of the reclamation was required to be formed to +6.0mPD. The final excavation level for the shaft at the deepest point was required to be at approximately at -17.5mPD. The Marine Deposits and underlying alluvial clays were left in place at the launch shaft location and therefore vertical band drains with soil surcharge were adopted as the ground improvement measures to accelerate the consolidation to strengthen the ground and limit any residual settlements both inside and outside of the shaft. The ground level

Fig. 2: Site Layout on Northern Landfall Area The Bridge and Structural Engineer

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adjacent to the shaft was maintained at a level of +6.0mPD with the exception of the northern side where it was raised to a level of +12mPD to increase the overburden pressures to facilitate the Tunnel boring machine launching.

The alluvium is underlain by the granite which includes a weathered layer of Completely to Highly Decomposed (Grade V/IV) Granite (CDG/HDG) that progressively improves to moderately decomposed (Grade III) or better Granite with depth. Typically, the weathered profile is consistent with a few metres of variation within the launch shaft area. At the northern end of the shaft there was evidence of a possible geological structure, which resulted in an increased thickness of the weathered material. The geology is summarized in Table 1 below.

3.

Northern Launch Shaft Geometry

3.1 Conventional TBM Launching Systems The conventional excavation and lateral support system use for the launching of typical

sized tunnel boring machines is illustrated in Fig. 3 below.

For large tunneling projects, it is common to adopt a simple braced excavation supported by diaphragm walls of similar to house the launching equipment for two machines side by side. With a typical large diameter tunnel boring machine of up to 10m it is possible for this system to span vertically to provide sufficient working space for the tunnel boring machine launching operations but requires a number of horizontal struts and waling beams to provide lateral support, which, due to high lateral load from the newly reclaimed land and sea would be expected to be bulky which would limit the use of excavators and vehicles inside making excavation slow. For a machine with an external diameter of 17.2m, this approach becomes practically infeasible due to the need for a minimum clear height of 19m inside the excavation and therefore an alternative approach was required.

Table 1: Soil Conditions at the Northern Launch Shaft Stratum

Elevation of Top (mPD)

Thickness (m)

Description

Reclamation Fill Marine Deposits Alluvium

+6.0 to -10.0 -10.0 to -13.2 -12.2 to -14.9

16.0 to 19.2 1.5 to 3.5 2.5 to 7.4

Completely/Highly Decomposed Granite (V/IV)

-16.1 to -20.1

14.0 to 21.3

Moderately or better Decomposed Granite (III/II)

-33.0 to -39.5

Not proven

Public Fill Soft silty clay Loose to medium dense layers of silty and clayey sand Extremely weak to weak completely to highly decomposed granite Moderately strong to strong moderately to slightly decomposed granite

Fig. 3: Typical TBM Launching ELS Scheme 60

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The Bridge and Structural Engineer

3.2 Innovative TBM Launching System Adopted for the Tuen Mun – Chek Lap Kok Link Due to the large dimensions of the two tunnel boring machines used for the Tuen Mun Chek Lap Kok Project, it was determined that a minimum clear space of approximately 100m length by 42m width by 19m height was required for their installation and launch. In order to provide this amount of open space an innovative excavation and lateral support solution using a strut free multi-cell system was adopted as illustrated in Fig. 4 below.

Fig. 4: Interconnected Cellular Cofferdam Solution

The multi-cell shaft comprised three interconnected circular diaphragm walls forming Cells 1 to 3 as shown in Fig. 5 with approximate dimension of 100m by 50m. The cells are designed to work in hoop stress by transferring the radial earth pressure forces acting on the outside of the excavation in compression around the perimeter walls.

In doing so, the only lateral support required for the excavation was provided by the two

cross walls and two cross beams between Cells 1 & 2 and Cells 2 & 3.

4. Northern Launch Shaft Design 4.1 Design Overview The shaft was formed by a series of diaphragm wall panels with a varying thickness of 1.2m in Cell 1 and 1.0m in Cells 2 and 3. Glass fibre reinforcement was installed across the soft eye openings at the northern end and a large concrete tympanum cast in front to support the shaft during and after the tunnel boring machine launching. Internally the hoop stresses are transferred across the excavation through a combination of two low cut-off cross walls and two flying beams which have a dual purpose to support the gantry crane for installation of the tunnel boring machine components. Due to the stresses which were transferred across the excavation due to the tall span and low cutoff arrangement to facilitate construction works within the shaft, the cross-wall thickness was 1.2m.

4.2 Design Analysis Due to the complex nature of the launch structure it was necessary to use advanced numerical analysis software to model both the geotechnical and structural behavior of the structure. As no single program was considered adequate to accurately model each situation it was decided to undertake a parallel analysis using Strand7 and Plaxis 3D. The Strand 7 model used 2D plate elements to model the diaphragm walls, slabs and struts while the Plaxis 3D model was used to derive the earth pressures, water pressures and soil springs as inputs into the structural model. A typical illustration of the two models is shown in Figs. 6 and 7.

Fig. 5: Interconnected Cellular Cofferdam Solution The Bridge and Structural Engineer

A complex construction staging sequence was modelled in each of the programs to identify the governing case load combinations with continuous iteration between the structural and geotechnical models until convergence Vol. 48 | Number 4 | December, 2018

61

Fig. 6: Typical View from the Plaxis 3D Model

Fig. 7: Interconnected Cellular Cofferdam in the Strand 7 Model

was achieved. The combined use of the two 3D modelling tools enable optimization of the structural elements for the multi cofferdam.

4.3 Y-Panels and Flying Beams Due to the high stress concentrations that exist at each of the intersection points between cells, special Y-panels were designed between the adjacent circular arcs to allow for transfer

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of the hoop stresses between cells and across the excavation. The Y-panels were formed from three bites from a diaphragm wall cutter with suitable stop-end details to create angled connections to abut the arching diaphragm wall elements from the cells on either side.

The stem was necessarily deep and heavily reinforced to accommodate the large bending stresses imposed induced by spanning 19m between the flying beams at the top level and the cross walls beneath. The flying beams were required to traverse the excavation to not only provide support to the full lateral earth pressures acting on the upper parts of the structure but also to support the weight of the gantry crane and tunnel boring machine components that it carried for the tunnel boring machine assembly. The flying beams were a critical component to the design of the cofferdam structure which is a characteristic of this design approach where the success of the entire system relies on the integrity of each of the component parts that form the system.

The Bridge and Structural Engineer

5.

Northern Launch Shaft Construction Programme Benefits

By comparison to a conventional cut-and-cover excavation and lateral supporting cofferdam, the multi-cell cofferdam was arguably more complicated to design and construct due to the need for each panel to follow a particular geometry with less tolerance for any deviation to ensure that the hoop stresses are carried continuously and properly around the perimeter of the structure. Similarly, the structure also included a number of critical and very heavily loaded cross walls and flying beams with complex Y-panel connections to ensure a direct transfer of forces across and between the structural elements. However, notwithstanding the design and construction complexities, it is considered that these measures are an investment of time and materials as the system thereafter introduces a number of key benefits to the construction. Most importantly, the cofferdam can be excavated freely and continuously without interruption in an open space without the need for multiple strutting layers nor complex excavation sequencing. As a result, the total construction time for the 100m length of structure was significantly reduced to only around four months of which the excavation only took around one a half months

leaving a strut-free environment for preparing and launching the tunnel boring machines yielding significant programme and safety advantages for the contractor. A photograph showing the launch of the largest tunnel boring machine is given below in Plate 1.

6.

Conclusion

The Tuen Mun – Chek Lap Kok Link northern section is a record breaking project with the inclusion of the world’s largest tunnel boring machines ever used for construction in the world and the first use of multi-cell shafts in Hong Kong.

The innovative adoption of these shafts has provided a simple and elegant solution to a challenging problem for excavation support by making use of the interlocking circular cells to form a strut free elongated open excavation, with only two buried cross walls and two flying struts to interfere with the works progress inside that latter of which were given a dual purpose to support the machine gantry to serve the excavation needs. No other lateral support was required for the multicell shafts, which greatly increased the working space in the shaft providing a safe open environment for working which enhanced both the speed of construction and speed of launching by allowing the use of larger shaft construction vehicles.

Acknowledgements

Plate 1: Northern Launching Shaft TBM Launch (Courtesy of Dragages-Bouygues Joint Venture and Highways Department, HKSAR Government)

The Bridge and Structural Engineer

The writers are grateful for the support of Highways Department, HKSAR and Dragages-Bouygues Joint Venture for the opportunity to have been involved with such an exciting and rewarding project which has extended the boundaries for technical excellence in the region through the introduction of a number of key innovations that were necessary to overcome the challenges afforded by the project.

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IMMERSED TUNNEL FOR BOSPHORUS CROSSING

Emre DUMAN

Nurettin DEMIR

Tolga PULAK

Lead Design Manager SYSTRA Mumbai, Maharashtra, India eduman@systra.com

N. Africa Regional Man. NUROL Co. (Turkey) Algier, Algeria ndemir@nurol.com.tr

Deputy Project Director Obrascon Huerta Lain Istanbul, Turkey tolga.pulak@ohl.com.tr

Emre Duman, born 1981, received his civil engineering degree from Istanbul Technical University.

Nurettin Demir, born 1951, received his civil engineering degree from Middle East Technical University - Ankara.

Tolga Pulak, born 1973, received his civil engineering degree from Gazi University - Ankara.

Summary The Marmaray Project Contract BC1, namely Bosphorus Crossing-Tunnels and Stations, of Istanbul City of Turkey, is a fast rail-track transportation scheme through a new underground route including a double cell immersed tube tunnel (IMT) of 1.4 km installed under Bosphorus. The IMT is unprecedented among about 150 various immersed tube projects in respect of the depth of 60 m and the flow speed of 2.5 m/sec at the surface and a reverse flow of about 1.0 m/sec at lower sea water levels.

The design features as well as the related design criteria, construction planning and method statement for fabrication, marine works, towing and immersion of the IMT elements are described in the present paper.

transportation capacity for about 150.000 passengers per hour in both directions of the route and to reduce the present total travelling time of 185 minutes by nearly half.

13.6 km is a new underground route within the scope of the EPC Contract BC1, namely Bosphorus Crossing, which is constructed by the Joint Venture of the Contractors TAISEI from Japan, GAMA and NUROL from Turkey. Project, designed for a lifetime of more than 100 years, consists of a twin route of 1.4 km immersed tube tunnel (IMT), 9.7 km TBM tunnels, 2.0 km NATM tunnels, 0.5 km of cut-andcover stations (no 2), a mined station and two at-grade stations (Fig. 1).

Keywords:Marmaray Project, Bosphorus Crossing, Immersed Tube Tunnel, IMT 1.

Introduction

The Marmaray Project is a modern fast railtrack transportation scheme of 76.3 km connecting the European and Asian sides of the Istanbul City underneath the Bosphorus at a depth of 60 m.

The objective of the Project is to establish a

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Fig.1: Scope of Marmaray Project – Contract BC1 The Bridge and Structural Engineer

2.

Immersed Tube Tunnels for Bosphorus Crossing

The immersed tube tunnels (IMT) of the Bosphorus crossing are unprecedented among about 150 various immersed tube projects in respect of the depth of 60 m and the flow speed of 2.5 m/sec at surface and a reverse flow of about 1.0 m/sec at lower sea water levels.

2.1 Layout and section of IMT The IMT are connected to the TBM tunnels at European and Asian coasts of the Bosphorus.

Total length of 1387 m of IMT consists of 11 elements with the size of 15.3 m wide by 8.6 m high by maximum 135 m long as shown herein below. The immersed tube tunnels are located into a trapezoidal channel prepared in the sea bed prior to the immersion.

2.2 Design criteria The basic design requirements are as follows: i.

Design Basis Earthquake

: Mw = 7.5

ii.

Countermeasure for Liquefaction

: Compaction grouting

iii. Huge Water Pressure : ~ 6 bar iv. Rapid Current Upper Layer (N to S)

: Max. 5 knots (2.5m/sec)

Bottom Layer (S to N)

: Max. 2 knots (1.0m/sec)

Fire Resistance

: 100 MW hydrocarbon fire minimum 4 hours : No early-age crack, >100 years design life

v.

vi. Concrete vii. Marine works under risks

: > 55 000 very large vessels/year

2.3 Immersed Tube Tunnel Elements

Fig.2: Major Immersed Tube Tunnels’ depths

TBM tunnels enter into the seabed at both sides to enable the connection with IMT using the advantage of shallow depth and steep slope. Seismic joints are provided at the connection of IMT with the TBM tunnels for damping off possible 3-dimensional seismic movements.

A tube element consists of a main body and two end-shells at each end. The end-shells are strengthened sandwich sections of the tubes to be closed with steel bulkheads to withstand the water pressure being subjected during and after immersion.

The body of a tube element is built with reinforced concrete cast inside a water-proofing steel membrane, manufactured in the factory in Izmir and transported to the fabrication yard. The water-proofing steel membrane remains as integrated into the permanent structure of the tube element, as shown herein below, that cathodic protection is applied by means of sacrificial anodes.

Fig.3: Profile and cross-section of IMT The Bridge and Structural Engineer

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Fig.4: Typical cross section showing dimensions and fabrication stages

The outfitting details and the fabrication steps are described on a typical cross section in Fig.4. The elements are equipped with the following outfittings, as shown herein below, for safe and proper execution of the marine operations.

•

Vertical and horizontal jacks; jacks moving in every direction for the fine adjustment of the element after immersion

•

Measuring device; a frame to place supersonic sensors to be used during immersion for relative positioning

•

Lifting lugs; hooks for the wire connection with the placing barge

•

Bollards; used for docking of the element

•

Grout curtain; a steel barrier to avoid under base grout to reach to the jacks

•

Temporary man shaft; temporary access shaft during testing and towing operations

•

Temporary access shaft lower part (for E11 only)

•

Survey tower (for E11 only); for the first immersion operation.

3.

Construction Planning and Implementation

3.1 Tunnel element fabrication Fabrication of the immersed tube tunnel elements are performed in two main stages: (i) Construction in dry docks consisting of the outer steel structure, the reinforced concrete base slab and first level of walls. (ii) Construction in harbor while floating consisting of the upper level of walls and the top slab of the reinforced concrete tube.

Fig.5: 3D illustrative image showing main parts and key outfitting installations of an element

•

Rubber gasket; seal for hydraulic pressure connection between elements

•

Bulkhead; closing covers of tubes resisting against hydrostatic pressure

•

Setting guide; a frame with pulling jacks to move elements to a closer distance fabrication stages

•

Pulling jack; a jack penetrates into jack box to pull the newly immersed element to the place for hydraulic connection

•

Ballast tank; water tanks for increasing the weight of the tunnel for immersion operation

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To minimize the fabrication time, two dry docks were prepared in the fabrication yard, each separated from the sea by means of movable watertight bulkhead gates such that the element, after the first stage, could

Fig.6: Aerial photo of tunnel fabrication yard in Tuzla, 30 km east of Istanbul The Bridge and Structural Engineer

be towed out to the harbour for execution of the second stage.

The first fabrication stage (dry dock), as shown in Fig.7, commences with erection of the steel end-shells at the two ends and the waterproofing steel membrane in between. The steel membrane is used as the outer framework for the reinforced concrete section. Each end-shell is built with nine sandwich type steel sections embedded by a self-compacting concrete. The first and last immersed tube tunnel elements, namely E11 and E1 respectively, are equipped with sleeve pipe sections to allow connection with the TBM tunnels.

Besides, the element E11 is equipped with an access shaft basis, specifically called hybrid.

The reinforced concrete body of element is built in three steps; the bottom slab of about 2300 m3 is cast continuously as a single lift lasting about 40 hours.

The two side walls and one inner wall are cast separately up to the mid-height, however, to avoid uncontrolled cracking, crack inducer contraction joints are provided at every 15 m along the longitudinal direction, which are filled up with special joint sealants afterwards. After completion of the bottom half of each element, the dry dock is flooded so that the element was moved by floating to the outside harbour where the upper wall and slab were cast from the pontoons. A special waterproofing membrane is placed over the top slab and a protection concrete layer is cast for the coverage. A complete empty tube element remains floating with a unit weight of nearly 0.97 t/ m3 and sometimes a concrete ballast is required on the top to secure balance of the element.

3.2 Marine works in Bosphorus (pre-immersion) 3.2.1 Soil Improvement

Fig.7: Steel construction of a newly started tunnel element in dry dock

Based on the results of the seismic analysis, soil improvement was required in some sections to avoid risks of liquefaction during earthquakes. Liquefiable

Fig.8: Steel fabrication in dry-dock

Fig.9: Dry dock is flooded (left) and element is towed out to the harbour (right) The Bridge and Structural Engineer

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dredging – is executed by a barge dredger unit with a 27 m3 grab. The side slope of the trench shall not be steeper than 2-horizontal 1-vertical.

Fig.10: Geological profile showing soil improvement zones

soils, identified in 2 sections as shown in the following figure, were treated by compaction grouting and soil replacement.

More than 2750 grouting columns were performed in a section of around 500 m to eliminate the liquefaction potential on the IMT foundation. For the compaction grouting, a very stiff mortar is injected into the soil under high pressure. The grout material during injection remains in a homogeneous mass and expands in size resulting in a displacement and densification of the surrounding soils. The results are verified by cone penetration tests (CPT) based on the cone and skin friction resistance.

A preliminary bathymetric survey was performed prior to dredging to determine the sea bed profile. Dredging proceeded based on the data obtained from a sonar system installed on the dredger. Finally, a bathymetric survey is redone to identify completeness of the sea bed excavation.

Dredged soil was carried in barges, pushed by boats, and disposed into a depression hole existing in the Marmara Sea.

3.2.2 Access jetty construction The access to the IMT during the construction time is maintained through the access shaft provided on E11. The access to this shaft is secured through a temporary jetty and a cantilever suspended connection bridge constructed at the Uskudar shore as shown herein below. A ship barrier was constructed on the upstream side (north) of the jetty to prevent collision to access shaft due to the heavy traffic in the Bosphorus.

Fig.12: Dredger dumping excavated soil into the barge

3.2.4

Element Foundation

After the final dredging, a gravel foundation was formed to support the IMT elements. The work consists of cleaning of the trench, gravel placement and grading. A final cleaning is made to ensure that the trench bed is clear off mud and sediments. Then, the selected gravel material is dumped into the position through a tremie pipe extended from a barge and the layer is levelled by means of a blade attached to a steel frame. The gravel foundation profile was then checked by a bathymetric survey.

3.3 Towing

Fig.11: Aerial view temporary jetty and access shaft 3.2.3 Dredging

Removal of the marine deposits to form a trapezoidal shape trench at the sea bed for installation of IMT –

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When an IMT element is fully completed, it is towed out from the construction harbour and docked to the placing barge. Then, the placing barge together with the element is towed to the position (Princess Island shores) for installation of the out-fittings and testing.

During the immersion testing, the IMT element is fully immersed into the sea down to a depth about 30 m where waterproofing and all other operational equipments such as surveying tools, electrical

The Bridge and Structural Engineer

Fig.13: Illustration of gravel dumping (left) and grader testing in the ground

Fig.14: Route of IMT element (left) and placing barge

connections etc. are tested. Following the decision for immersion, the element is towed with the placing barge to Bosphorus as illustrated in the following layout.

for the decision of GO/NO GO for the immersion operation of the tunnel element. According to input data, model develops current velocities in the incoming immersion period.

3.4 Immersion

3.4.2 Mooring

3.4.1

Positioning of the placing barge is controlled by 13 anchors; some for mooring only and some for handling.

Immersion of an IMT element can only be commenced after proper positioning of the placing barge. At first, anchors are placed and tightened to the calculated coordinates to make the placing barge parallel to current so that the element can face the strong upper current with its cross section. As the immersion continues, the current velocity decreases gradually. Then, the barge with the submerged element is rotated by changing the anchor locations and wire lengths to match with the design position.

Go/No Go decision

Since the current is generally too strong for an immersion operation in the Bosphorus, a current forecast model was developed to obtain a reliable idea of the current velocity in advance. The process includes (i) Hydrological survey, (ii) Online monitoring and (iii) Forecast modelling.

The purpose of the hydrological monitoring is to obtain hydrological and meteorological conditions, such as current, water level, stratification due to salinity, temperature, wind and atmospheric pressure to be used to set up the forecast model. Online monitoring is carried out to monitor the hydrological condition at the immersion site on the Bosphorus. Afterwards model is run and calibrated with the real-time online monitoring results. The resulting forecast model is used

The Bridge and Structural Engineer

3.4.3 Immersion operation of E11 Immersion operation of the first element (E11) is different from the other elements because no hydraulic connection is required. When the barge is moored into

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Fig.15: Location of monitoring stations (left) and model output

Fig.16: Illustration of E11 immersion

the required location, immersion starts by taking water into the ballast tanks and continues down to -15 m.

Then, the placing barge is rotated to its original location and immersion continues. Adjustment of anchor wire lengths may be necessary, because the drag force of the current may change the position of the element.

Immersion is completed roughly in the tolerances by placing the tunnel over the gravel foundation with the vertical and horizontal jacks. Finally, wires connected to the lifting lugs are released by diver operation and placing barge is disconnected.

3.4.4

Access shaft installation

Access into E11 was maintained until completion of all activities. Lower part of the access shaft (basis) was already installed in the fabrication harbour. Upper part was brought into the position over a crane barge connected to lower part with a flexible waterproof joint with divers’ operation.

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Fig.17: Access shaft installation

3.4.5 Final adjustment of elements Final adjustment of the element positioning is achieved by means of vertical and horizontal jacks directed by cable remote control. E11 has two pairs of vertical and horizontal jacks at each side. The other elements are equipped with only two vertical and two horizontal jacks inasmuch as the connection side is fixed.

3.4.6

Immersion of other elements

Immersion operations of other elements are performed under the same principles, except a hydraulic vacuum

The Bridge and Structural Engineer

Fig.18: Fine adjustment of tunnel element by jacks

Fig.20: Monitoring system of immersion

3.5 Marine works immersion) 3.5.1

Fig.19: Mechanism of vacuum connection (P.E.: Preceding Element, I.E.: Immersed Element)

connection is applied on the existing element; once the new element comes nearer to the existing one, a pulling jack is released from the existing one and plugs onto the new one’s jack box and pulls that with a resulting 4 cm compression on the gasket providing a limited sealing. From this point, dewatering of the water trapped between two elements starts and finally a complete vacuum is achieved. A temporary but robust connection is thus maintained. This operation is controlled inside the tunnel since access to the existing element is achieved through the access shaft after removal of the bulkheads.

in

Bosphorus

(post-

Underbase grouting

After positioning of an IMT element, underbase grouting is required of the space between the bottom of the element and the gravel foundation. At first, grout stoppers are formed around the perimeter of the element to confine the underbase space to be filled by grout. The grouting is made inside the element through the pipes and valves installed during fabrication. A 3-component plasticized special grout mix is applied for underbase grouting. Mixing is made at the nozzle and the grout mix becomes a gel like viscous liquid such that washing out inside the water is prevented. Volume check of filling material is done by the control valve points during process. As shown in the following figure, another key feature of this gel like material is that it does not penetrate into the gravel foundation such that additional pore pressure increment inside the porous underbase is prevented, which would otherwise increase the soil liquefaction risk in case of an earthquake.

3.5.2

Backfilling of IMT

Backfilling of IMT consists of locking fill, general fill, armour protection and anchor release band. All type of material is selected rockfill and mainly dumped through a tremie pipe from a barge whereas the large boulders for anchor protection are placed on top of the backfill by means of a special handling crane. The

3.4.7 Measuring system for positioning of elements Position of placing barge before immersion is maintained by GPS and gyrocompass. Multi-beam is used for the submerged element positioning.

Measurements to check the relative positioning of an element in respect to existing one is performed by three-dimensional supersonic sensor.

The Bridge and Structural Engineer

Fig.21: Mix soil filling

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locking fill is crushed rock type material up to particle size of 200 mm to prevent lateral displacement of the elements.

A final bathymetric survey is performed after completion of each layer to check and verify the asbuilt lines and grades with respect to the design.

Fig.23: TBM is excavating towards sleeve (left), explodes waterstop packing

The space between the elements E1 and E11 and the sloping sea bed on shores of the European or Asian sides is filled with selected mix soil material as shown in the figure. This cementitious material is relatively impermeable with a strength of about 1MPa. 3.6 IMT-TBM connection In the fabrication harbour, sleeve pipe is filled with LW material which is a type of liquid glass and this material is frozen prior to immersion.

TBM penetrates into LW and the waterstop packings are exploded so that removal of the end-shell bulkhead becomes possible without flooding. Shield of TBM is left as an outer form so that the TBM can be dismantled. An in-situ concrete lining is cast finally.

Fig.24: Successful connection of TBM and IMT

4.

Fig.22: Concept of TBM-IMT connection

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Conclusion

An immersed tube tunnel of 1.4 km has been implemented under the Bosphorus at a depth of 60 m, the deepest ever constructed so far, within the scope of the Marmaray Project Contract BC1, which is a fast rail-track transportation scheme connecting European and Asian sides of Istanbul. The IMT has a lifetime of more than 100 years, like all components of the Project, and has been constructed within a reasonable range of cost alike the similar projects. A cost optimization can be achieved with immersed tube tunnels owing to relatively shallower depth and thus shorter length, which would be deeper and longer in case of bored tunnels through the underlying bed rock.

The Bridge and Structural Engineer

EARLY-AGE STRENGTH DEVELOPMENT MONITORING OF SHOTCRETE TUNNEL LININGS – CURRENT PRACTICE Dr Vishwajeet Ahuja holds a wide array of experience in NATM/Conventional Tunnelling. He has worked on variety of railway and road tunnelling projects, such as Dulles Metrorail, Mumbai Metro and Rohtang, involving both the soft ground and hard rock conditions.

Dr Vishwajeet Ahuja Sr Design Engineer (NATM) Louis Berger, India vishwajeet.ahuja@gmail.com

Abstract

1.

Shotcrete tunnel lining is an important part of soft ground tunnelling. It provides immediate ground support and maintains tunnel stability. A quick set and rapid strength development of freshly sprayed shotcrete are crucial for maintaining shotcrete lining integrity. An inadequate strength development leads to the lining failure and tunnel instability. This poses serious health and safety risks to construction workers and nearby structures. Therefore, early age strength development monitoring forms a crucial aspect of tunnel construction. Currently used testing methods, namely needle penetrometer, stud-driving and uniaxial compressive testing of cored samples, are of destructive nature. To avoid damage to the freshly sprayed lining and to mitigate safety hazards to testing operatives, testing is performed on test panels. Current test methods, however, test a very small part of the shotcrete. Since the temperature histories of the lining section are different from the test panels, the outcomes are local in nature and provide an incomplete picture of the shotcrete lining strength gain. Thus, there remains a need for a test method with a capability of testing large volumes of the shotcrete works remotely, holistically and non-destructively.

Underground spaces have been in use for thousands of years to meet various requirements, such as resource mining, dwelling or infrastructure.

Underground infrastructure comes in different forms – transportation (such as highways and railways), conveyance (such as hydropower, sewage, storm water, and pipelines), and storage caverns (such as petroleum or natural gas). There are two approaches for creating an underground space, namely open excavation and closed excavation. The open excavation approach leads to buried infrastructure, such as water pipelines and utility cables, and the closed excavation approach leads to infrastructure installed at shallow or significant depths, such as sewage tunnels and urban rail tunnels. Both methods have their own ground support requirements. Various types of geotechnical support systems have been developed and are prescribed as required.

The maturity method is well established nondestructive approach for normal concretes and allows maturity and hence strength to be calculated from a temperature history.

Keywords: Conventional tunnelling, shotcrete, shotcrete tunnel lining, maturity method, early-age strength development.

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Introduction

Concrete, under different names, tends to find its place in these support systems. Concrete classification is based on the aspects such as the method of preparation (precast concrete), the method of installation (cast in-situ concrete), purpose (backfill concrete), and ingredients (reinforced concrete). One such classification is the shotcrete and finds its use in the both excavation approaches. This paper investigates the early age strength development of a shotcrete mix when used as a closed excavation support measure, and the application of Arrhenius equation based maturity method on to the shotcrete lining.

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2.

Shotcrete

Shotcrete (also known as sprayed concrete) is defined as concrete that is conveyed through a hose and pneumatically projected at high velocity onto a surface [1]. The high velocity spray leads to placement and compaction at the same time to produce a dense homogeneous mass, allowing its application to any type or shape of surface, including vertical and overhead areas.

There are two placement methods, namely the ‘wet process’ and the ‘dry process.’ In the wet process,

the ingredients are mixed and conveyed through a pipeline to the nozzle to be pneumatically placed. For the dry process, the dry ingredients, such as cement and aggregates, are mixed and conveyed through a hose to a nozzle where water is added. Fig. 1 show the schematics of the wet and dry processes, respectively. In the case of the shotcrete lining works, an accelerator (typically in liquid form) is also required for immediate set, and is typically added at the nozzle for both the wet and dry processes. Once the accelerator has been added, the shotcrete sets soon after and hardening begins.

Fig. 1: Spray process (a) dry mix and (b) wet mix spray process

Each process has its own pros and cons, which act as trade-offs based on the placement requirements.

For example, the dry process suffers from disadvantages of less control on water content and aggregate, and high dust [2]. On the other hand, the wet process requires extensive logistical arrangements, and it becomes inefficient for small volumes. The dry process is well utilised when small volumes are required intermittently. From the perspective of quality control and Health & Safety, the wet process is usually the preferred method.

prescribed immediate application of shotcrete in conjunction with other ground support measures such as rockbolts and lattice girders to prevent ground loosening [3]. Later on, the aspect of ground strength mobilisation was added to the NATM philosophy. In all cases, the support measures must be installed before the ground loosening can begin, i.e., within the ground stand-up time, and are required to provide immediate response to the ground loading. Fig. 2 shows a typical NATM support system as adapted for metro rail tunnel in soft ground.

3.

In soft-ground conventional tunnelling, the short standup time leaves shotcrete as the preferred measure to provide quickest ring closure for full-face tunnel support. To sustain the on-coming ground loading and prevent ground loosening, shotcrete must achieve an immediate set and undergo a phase of rapid strength development to “attain a high carrying capacity as quickly as possible” [4, p. 454]. Thus, shotcrete lining has special constructional as well as post-construction performance criteria; the most significant issues are listed below:

Shotcrete tunnel lining

With greater flexibility of application, shotcrete is frequently used on heavy construction projects especially during the excavation and support process of tunnel and shafts. When applied on to the excavation surface, it acts as acontinuous shell structure and is called as shotcrete lining.

Shotcrete lining, as designed and constructed today, has its roots in the New Austrian Tunnelling Method (NATM). NATM (or conventional tunnelling) 74

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Fig. 2: NATM support measures for a metrorail tunnel in soft ground

1.

2.

Constructional considerations: a.

pumpability through pump lines and hoses;

b.

adhesion to sprayed surface, reducing rebound and falls; and

c.

homogeneity from batching up till the placement.

Post-construction considerations: a.

early-age compressive strength gain;

b.

long-term compressive strength;

c.

ductile (tensile) failure;

d.

durability;

e.

fire resistance; and

f.

permeability for water-tightness.

The shotcrete mixes are tailored to achieve the performance requirements and are required to conform to standards such as EN 14487-1 [1]. The most critical factors are typically the early age strength and the pumpability requirements.

The key differences between a typical high strength concrete mix and a typical shotcrete are as follows: • •

higher w/c ratio to ease workability and spraying of pumped concrete; greater ordinary Portland cement content;

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•

properly graded aggregates;

•

maximum aggregate sizes to 10 mm;

•

use of accelerator to create an immediate set and accelerate the strength gain;

•

use of high range water-reducing (super plasticiser) admixtures to improve workability;

•

use of stabilisers/set-retarders to increase pot life of mixed concrete;

•

use of silica fume to improve immediate adhesion;

•

use of fibres to achieve uniform crack control.

Thus, the admixtures are mainly responsible for modifying the fresh concrete behaviour during installation, and the post-installation mechanical performance is derived from the basic ingredients, namely cement, supplementary cementitious materials, water, and aggregates.

4.

Mechanical nature of shotcrete

Shotcrete, like any other Portland cement concrete, is a composite material consisting of a binding medium (Portland cement and water) within which are embedded particles or fragments of a relatively inert mineral filler. Initially, the binding medium is plastic in nature, with anhydrite cement occurring as dispersed particles in the water. As the cement hydration progresses, the medium hardens to become a porous and permeable solid.

The upper limit of important mechanical properties of the concrete, such as strength and stiffness, are largely related to the upper limit of the density of matrix. This is so because more porosity is observed in the binding medium and less in the aggregates. While the required values of mechanical parameters for the shotcrete are project specific, many of them are prescribed based on an understanding of the method of construction. Typical mechanical parameters for the shotcrete are presented in Table 1.

Table 1: Typical properties of shotcrete Property

Unit

Age

High quality shotcrete

Compressive strength MPa

1 day

>20

Compressive strength MPa

28 days

60

Tensile strength

MPa

28 days

>2

Initial setting time

mins

(start - end) 1 – 3

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Property

Unit

Age

High quality shotcrete

Density

kg/m3 -

2150 – 2300

Total porosity

%

-

15 – 20

Permeability

m/s

-

<2.0 x 10-12

In summary, the concrete’s compressive strength depends on density. The density can be improved by maximising binding matrix hydration and improving the binding matrix – aggregate interaction.

4.1 Shotcrete strength development As mentioned earlier, the strength development or hardening of concrete occurs as the cement and water reaction, or cement hydration, progresses. The hardening process may be subdivided into four phases, as described in [5] and is shown Fig. 3: • • • •

fresh concrete; early age; “almost” hardened concrete; and hardened concrete

4.2

Shotcrete strength determination

Mechanical testing for shotcrete requires more input than typical concrete strength testing. Due to the importance of early age strength development, stringent testing criteria have been developed[3]. Due to the construction method of the shotcrete lining, insitu testing is the most suitable approach for strength determination. Although, from the personnel safety perspective, it is not appropriate to perform in-situ tests until the lining has achieved sufficient strength (usually above 0.5 MPa). Therefore, test panels are used for the early age testing. The test panels are required to be sprayed simultaneously with the lining as this will provide the most appropriate strength development profile [6]. Typical strength development specifications have been defined as curves and are referred to as J1, J2 and J3 curves [7] and are shown in Fig. 4.

Strength

Fresh concrete is referred to as the visco-plastic or setting stage. It can be moulded easily. Once concrete sets, hardening begins. It marks the beginning of the early age. There is no precise definition of end of early age, and may last varying from a few hours to more than a week. For tunnelling, the shotcrete early age phase passes in less than 24 hours, with a critical observation period of up to 3-day age. After that, the hardened shotcrete would be able to form a rigid shell support.

Further hardening stages are achieved as hydration progresses. The stage of peak rate of hydration can be marked as the beginning of the “almost” hardened concrete. One could mark the end of “almost” hardened concrete to the phase of arrival of a diminished rate of hydration that is equivalent to the rate of hydration at the beginning of early age of the concrete (post setting) with the concrete having achieved the mechanical properties similar to that of the fully hardened concrete. Typically, 28-day strength is assumed to be fully hardened concrete. After this age, the hydration process has slowed down such that rate of strength development may safely be assumed to have converged, though, this process may last for decades, and the achieved strength may be substantially greater than 28-day age.

“Almost” hardened concrete

Hardened concrete

Fresh concrete

Early age

Setting

1-3

28

Age, d

Fig. 3: Phases of concrete strength development [5]

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Fig. 4: Early strength classes of young sprayed concrete (redrawn from EN 14487-1:2005) The Bridge and Structural Engineer

The European Norm EN 14488-2 [6] has specified two stages of testing for early age strength – needle penetration and stud driving. These tests are valid for a limited range of strength values beyond which core testing is used. Cores may be taken from the sprayed panel or the tunnel lining. Table 2 summarises different testing methods and related general information typically used for shotcrete tunnelling works.

Needle penetration test For penetration needle testing, a penetrometer with a 3mm diameter needle and capable of recording force to an accuracy of 10N is required. The penetrometer needle measurements can be as much as 30% off the true value [6] and thus, have a large margin of error.

Table 2: Typical SCL tests and related scope for urban tunnels Test Type

Strength range

Time and Frequency

Typical Test Apparatus

Penetration Needle

0.1 to 1.0 MPa

Up to 1 hour Mins –15, 30, 60

Meyco Penetrometer

Stud Driving

3.0 to 16.0 MPa

Up to 24 hours Hours – 3, 6, 12 or as necessary

Hilti DX 450-CT with pull-out apparatus

Core testing (Cores from panels / lining)

16.0 MPa or more

Up to 28 days Days – 1, 3, 7, 14, 28

Compression Testing machine

Stud driving test Stud driving is a two-step test – percussively firing a calibrated stud and thereafter, a stud pull-out with tensile loading equipment. The calibration relationships provided in EN 14488-2 [6] are used to convert the penetration depth of the stud into the shotcrete and pull-out load into strength equivalent to a 200 mm cube[8].

Hilti Corporation [8] has developed an additional testing method using same apparatus, called ‘specialmethod’, to determine strengths in the range of 17 – 56 MPa. Thus, the earlier method can be referred as standard stud-driving method, while the latter method can be referred as special stud-driving method.

Core testing The later age compressive strengths of shotcrete, typically 24 hours onwards, are normally determined from cylindrical cored samples. These cylindrical cores are drilled from the shotcrete panels and/or linings for final strength compressive strength determination.

Typically drilled core diameter is 100 mm and height can be specified to be one or two times the diameter.

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These tests provide cylindrical compressive strength (MPa), and require a conversion factor (Kin-situ) for equivalent in-situ strength of a 200 mm cube.

5.

Case study – Whitechapel station primary lining

Whitechapel platform tunnelling works were part of the Cross-rail project at Whitechapel station in London, United Kingdom. The site work included construction of a complex layout of shafts, platform tunnels, cross passages and escalator barrels.

The tunnelling works involved sprayed concrete for both the primary and the secondary lining works. The case study was undertaken during primary lining works.

The shotcrete mix (Table 3) was designed for the wet spray process and was sprayed using a Meyco Potenza fitted with a Meyco Compacta boom. The concrete was pumped through Meyco Suprema 30, a double cylinder recipocatory pump, which was mounted on the spraying rig itself. The accelerator (Gecederal F 2000 HP) was fed into the nozzle of Meyco Potenza in liquid form and added to the concrete right before the spray.

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Table 3: Shotcrete mix at Whitechapel Station SCL works Content

Type

Quantity (kg/m3)

Ratio/dosage*

Cement

CEM I 52.5 N

420

-

Water

-

173

0.41

Aggregate

Limestone (0/4)

590

-

Aggregate

Marine Sand (0/4)

590

-

Aggregate

Limestone (2/6)

505

-

Microsilica slurry

EMSAC 500 S

52

12.38%

Retarder

Pantarhol 85 (VZ)

6

1.43%

Superplasticiser

Pantarhit T100CR (FM)

4.8

1.14%

Accelerator

Gecederal F 2000 HP

Added at spray

5.50% (averaged)

Steel Fibres

Steel HE 55/35

35

-

*Dosage in percentage (%) of cement weight basis

In-situ strength testing was made on the shotcrete test panels (sprayed on construction sites). The site testing involved spraying of two sets of five test panels, (thus, a total of 10 panels) under real time site conditions, where the five panels in each set were sprayed at once.

Each panel had a wooden formwork and provided a clear testing surface of 600 mm x 600 mm with a depth of 150 mm. The testing methods included the use of the Meyco needle penetrometer, and Hilti DX450CT testing apparatus for standard and special studdriving testing of the panels. Since each testing method is applicable for a certain range of strength, the test method at the time of testing had to be kept flexible.

Fig. 5 presents the strength testing outcomes of the two sets. It is observed that in spite of having same mix, both sets of panels exhibited very different strength development rate, especially till the age of 8 hrs. Afterwards, at the age of 12 hours, both sets exhibit similar strength.

The varied strength development occurred as both sets were exposed to different environmental conditions (such as exposure to equipment heat and ventilation), and hence different curing temperatures.

The curing temperature histories, alongside the respective strength development history, of the two panel sets has been shown in Fig. 6.

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Fig. 5: Strength testing results (Zones Z1, Z2, and Z3 represent strength estimates obtained using the penetometer, standard stud-driving, and special stud-driving method, respectively)

The lower curing temperatures of the Set 1 panels leads to slower cement hydration reaction, and is directly reflected in the shotcrete strength development. As previously noted, the prominent difference in strength of the two sets occurred till the age of 8 hrs. At the age of around 12 hrs, the difference is very minimal. Thus, it is concluded the impact of curing temperature on the early-age strength development becomes insignificant after the 8 hrs age.

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Fig. 6: Strength development and temperature evolution hisotry of the two panel sets demonstrating the effect of curing temperature on the early-age strength development The presented outcomes demonstrate that the curing temperatures at the very early age of the concrete are of great significance. Since the lower curing temperatures considerably impede the strength development process, these are not desirable in the case of the tunnel lining, where early age strength is of great concern. This aspect of temperature variation on the short-term and long-term concrete properties has been studied since the late 1940’s under the name of concrete maturity. The early studies led to the development of the ‘maturity method’ [9], and its application is demonstrated next.

6.

Maturity method for shotcrete

The maturity method is an approach of quantifying the temperature dependence of the concrete’s strength development. It involves study of the temperature histories to deduce concrete maturity and relate it the strength development to establish a strength – maturity relationship. The major steps in this approach are: a.

Thermal monitoring for temperature history;

b.

Maturity modelling using maturity function;

c.

Establish strength – maturity relationship; and

d.

Strength modelling of new concrete works.

e.

Thermal monitoring

The curing temperatures were measured at the surface of the panels using a thermal imaging c amera (Fig. 7). While the strength testing was performed on the wider area of the panel (Fig. 7a), the temperatures of the central core surface were used to prepare the shotcrete temperature histories (as noted in Fig. 7b).

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Fig. 7: Whitechapel station sprayed concrete (a) panel testing and (b) thermal monitoring

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The frequency of the thermal monitoring varied from every few minutes during the first hour after spraying to every 6 hrs after the age of 24 hrs. The thermal monitoring was undertaken for the test panels and the tunnel lining works.

6.1 Maturity modelling A maturity function models the cement hydration progression and the strength – maturity relationship relates the concrete strength development to its maturity development, where the concrete maturity is synonymous with the cement hydration development. The temperature sensitive exothermic cement hydration reaction is well represented by the Arrhenius equation based maturity function, and is given by:

Fig. 8: Maturity modelling for the Set 1 panels

( ) Ea

dξ RT –– = φ (ξ−ξ 0) Ae dt

where dξ/dt is the rate of cement hydration (s -1), φ(ξ-ξ0) is the normalised kinetics of cement hydration reaction as a function of degree of hydration (ξ), ξ0 is the threshold degree of hydration value after which the strength development begins, A is the affinity constant (s-1), Ea is the activation energy (J.mol-1), R is the ideal gas constant (8.314 J.mol-1.K-1), and T is the absolute temperature (K).

With the synonymy of the cement hydration and heat of hydration, the shotcrete mix was studied through the isothermal calorimetry at four isothermal conditions (namely 10, 20, 30 and 40°C). The calorimetric outcomes evaluated per the methodology explained in [10], and A = 36 s-1 and Ea = 38.4 kJ.mol-1 were established. The key aspect of normalised kinetics was also deduced for the calorimetric data and is shown in Fig. 9.

Typical concrete maturity modelling procedure uses the kinetics measured at a reference temperature (typically 20°C), and apply it for all temperatures using the following formulation: ti

xi = å f (xi - x 0 ) [A exp( - Ea /RT )] Dti 0

In case of the non-isothermal curing of shotcrete, using the reference temperature kinetics approach was unreasonable, and it was modified to utilise all

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Fig. 9: Normalised kinetics for Whitechapel station primary lining srayed concrete mix

four curves through interpolation for the intermediate temperatures. For example, at ξ = 0.3, normalised kinetics at 20 and 30 are 0.894 and 0.933, respectively.

To determine the normalised kinetics at 25°C, the two values are interpolated to arrive at the value of 0.913.

Figure 8 shows the outcomes of the maturity modelling made for Set 1 panels by utilising above described approach where Δti = 0.1 hrs was used. Since the maturity has been modelled in terms of the cement hydration reaction progression, the maturity was calculated between 0 and 1, and is referred to as the degree of hydration.

6.2 Strength – maturity relationship In this step, the strength data was plotted vs modelled maturity (degree of hydration in this case), and the strength – hydration relationship was assessed (Figure 10). It was found that both sets provided different relationship. The Set 1 relationship of y = 84.25x – 6.03 when written in terms of strength and degree of hydration would be as below:

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heterogeneity, and the nozzleman’s workmanship, leading to such variation. Though this variation can’t be quantified.

fc = 84.25 (x – 0.07) wherefc is characteristic compressive strength in MPa; and x is degree of hydration . This formulation indicates the shotcrete strength development starts after the degree of hydration of 0.07 has been achieved.

iv.

Maturity modelling: There is also scope of improvement in the maturity modelling approach.

There remains a need of more case studies to verify the modelling approach.

v.

Linearity of relationship: Another dimension could be that the presence of admixtures make the strength – hydration a non-linear relationship.

In any of the scenarios, more case-studies are required.

6.3 Strength modelling of shotcrete lining

Fig. 10: Stength – maturity relationship for Whitechapel station sprayed concrete mix

Similarly, the Set 2 relationship can be represented as fc = 51.83 (ξ – 0.06), and indicates that the strength development would start after the degree of hydration of 0.6 has been reached.

The shotcrete lining strength modelling involves converting thermal monitoring data to strength development information through maturity modelling and established strength – maturity relationship.

Similar to the panels, the lining was also thermally imaged. Fig. 11 shows a schematic of remote thermal monitoring of the lining section using thermal imaging.

The remote access allows the user to monitor lining without hindering the construction site works.

There are various reasons that could have contributed towards this scenario where same mix provides different relationship. A few of them are discussed below: i.

ii.

iii.

Cross-over effect: It is well known that the concrete cured at lower temperature will have greater ultimate strength when compared to concrete cured at higher temperature (Byfors 1980). Since Set 1 curing temperatures were well below than Set 2, such a variation would be expected.

Limitations of testing method: The standard studdriving method is suitable for up to 16MPa. Observing Set 2 strengths at degree of hydration of around 0.40, one may interpret that these strengths have been underestimated. Though, such a speculation can only be resolved, if insitu core testing had been made.

Workmanship: Due to its construction method, the shotcrete is prone to variations such as its

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Fig. 11: Remote thermal monitoring of the freshly sprayed shotcrete lining using thermal imaging

Fig. 12 shows an example of thermally imaged lining section monitored in concurrence to the panel testing.

In the thermal image, the crown area is typically exhibiting higher temperatures of around 45°C. The intermediate band of lower temperature of around 35°C is caused by the ventilation duct (hung at right shoulder).

The thermal monitoring of the lining requires selection of critical location of the lining section (namely crown, shoulders and springline level). Fig. 13(a) shows a schematics of the key monitoring location for a tunnel

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Fig. 12: Whitechpel station primary shotcrete lining (a) digital and (b) thermal image[11]

lining section. Fig. 13(b) presents the thermal monitoring data obtained from the thermal imaging made for the lining section at corresponding to the Set 2 panels.

The strength modelling used the maturity function input parameters noted in Section 6.2 and strength â&#x20AC;&#x201C; hydration relationship of Set 2 shown in Section 6.3.

7.

Conclusions

The current practice of shotcrete strength monitoring is limited to destructive testing of sprayed panels, and donâ&#x20AC;&#x2122;t account for impact of curing temperatures. Since shotcrete linings undergo very different curing conditions than the test sample (sprayed panels), the outcomes may not be true representation of strength development.

A case study was undertaken to demonstrate the impact of curing temperature using a non-destructive approach called maturity method. The case study 82

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Fig. 13 (a) Schematic for shotcrete lining thermal monitoring using thermal imaging, and (b) temperature histories and strength development modelling of 3 key locations of the lining section corresponding to Set 2.

demonstrated that the Arrhenius equation based maturity function is useful to model the hydration progression of the complex cementitious medium of the shotcrete mixes. It was also found that strength and maturity may not follow a linear but multilinear relationship.

8.

Acknowledgements

The presented case study was undertaken during the research work carried by the author at University of Warwick. The author is grateful for the support received from University staff. The author also expresses his gratitude to BBMVâ&#x20AC;&#x2122;s staff at Whitechapel station for kind support during the site testing programme.

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9.

References

1.

British Standards Institution, EN 14487-1 Sprayed concrete — Part 1: Definitions, specifications and conformity. London: BSI Standards Publication, 2005.

2.

3.

4.

E. H. King, “Shotcrete,” in Tunnel Engineering Handbook, J. O. Bickel, T. R. Kuesel, and E. H. King, Eds. Boston, MA: Springer US, 1996, pp. 220–230.

BASF, Sprayed concrete for ground support, 13th ed. BASF Construction Chemicals Europe Ltd., 2014.

L. von Rabcewicz, “The new Austrian tunnelling method – part I,” Water Power, vol. 16, no. 11, pp. 453–457, 1964.

5.

J. Byfors, “Plain concrete at early ages,” Swedish Cement and Concrete Research Institute, Stockholm, 1980.

6.

British Standards Institution, EN 14488-2 Testing sprayed concrete — Part 2: Compressive strength of young sprayed

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concrete. London: BSI Standards Publication, 2006.

7.

British Standards Institution, EN 14488-1 Testing sprayed concrete — Part 1: Sampling fresh and hardened concrete. London: BSI Standards Publication, 2005.

8.

Hilti Corporation, “Determination of the early strength of sprayed concrete with stud driving method with Hilti DX 450-SCT,” Alpbach, Austria, 2009.

9.

N. Carino, “The Maturity Method,” in Nondestructive Testing of Concrete, 2nd ed., V. M. Malhotra and N. J. Carino, Eds. Boca Raton: CRC Press, 2004, p. 47.

10. V. Ahuja, “Non-destructive approach for sprayed concrete lining strength monitoring,” PhD thesis, University of Warwick, Coventry, 2017.

11. V. Ahuja and B. Jones, “Nondestructive Approach for Shotcrete Lining Strength Monitoring,” Shotcrete Mag., vol. 18, no. 3, pp. 48–54, 2016.

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GUIDELINES FOR INSTRUMENTATION AND MONITORING IN NATM TUNNELS

Ali Hayri CUVENC

Archana

Mining Engineer MBA AECOM India Ali.Hayri@aecom.com

Tunnel Engineer, M.Tech.

AECOM India Archana.singh2@aecom.com

Ali Hayri Cuvenc, born 1949, received his Mining engineering degree from the METU Turkey in 1972. He worked in various companies as construction Manager, CEO, and Tunnels and Metros Design and Consultancy firms.

Archana, born 1983, received her civil engineering degree from NERIST and Masters from IIT Delhi in Rock Engineering & Underground Structures. She worked in various companies in Hydro and Metro Tunnel Design.

Abstract NATM (New Austrian Tunnelling Method), also known as Conventional Tunnelling Method (CTM) is widely used all over the world where the feasibility studies shows various constrains in terms of excavation geometry, constructability, length, geological condition, cost etc. NATM overcomes all types of constructability issues and extensively used on field with experienced personnel, regular optimization of design and Monitoring of excavated tunnel.

Underground works, constructed by Conventional tunnelling (NATM), include linear tunnels such as railway tunnels, motorway tunnels or hydro tunnels, and also hydroelectric caverns, underground storage caverns, metro and railway stations. The project site can be located at a shallow depth or under high overburden, in stable or unstable ground, under genuine rock pressure, below the phreatic surface or in dry conditions, the method is suitable. The Conventional tunnelling (or NATM) is the best for projects with highly variable ground conditions or for projects with variable shapes.

Geotechnical monitoring is to provide early information about tunnel behaviour in order to optimize excavation and support activities during construction and to recognise in time the requirements for remedial measures.

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Keywords: Ground, Rock Aggregate. Intact Rock, Rock mass, Soil.

Introduction Conventional tunnelling (or NATM) is carried out in a cyclic execution process of repeated steps of excavation followed by the application of relevant primary support, both of which depend on existing ground conditions and ground behaviour. The Conventional tunnelling (or NATM) method mainly uses standard equipment and allows access to the tunnel excavation face at almost any time. The method is very flexible in situations or areas that require a change in the structural analysis or in the design and as a result of this also require changes in the support measures.

1.1 General NATM is based on the concept that the ground around the tunnel not only acts as a load, but also as a load-bearing element. Typically, the excavation and support activities are continuously adjusted to suit the ground conditions, always considering the technical/ design requirements. The ground reaction, in the form of lining displacements is measured in order to check the stability of the opening and to optimise excavation and support process.

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1.2 Definition of conventional Tunnelling

9

Increase or decrease of support, e.g. the thickness of shotcrete, number and/or lengths of rock bolts per linear meter of tunnel, spacing and dimensions of steel arches, number and lengths of spiles, application of shotcrete at the tunnel face, bolting the face etc.

9

Variation of ring closure time - which is the time between the excavation of a section of the tunnel and the application of partial or full support - or variation of ring closure distance from excavation face.

9

Introduction of primary support ring closure.

9

Variation of explosives charge per blasting round and variation of detonator sequences. Other variations in the design enable one to react to changes in the stand-up time of the ground encountered.

9

Increased or decreased length of excavation round (common round lengths vary from 0.5 m to 4.0 m).

9

Partial excavation by splitting the excavation face into the crown, bench, and invert excavation steps or even further in pilot and sidewall galleries and in staggered bench/ invert excavations.

Generally two different methods are available for the construction of tunnels according to the tunnelling excavation procedure: Continuous tunnel excavation: Excavation by a tunnel boring machine (TBM) with continuous advance of the full tunnel face; Cyclic tunnel excavation: NATM with cyclic advance of the tunnel face. When required the tunnel excavation can be subdivided into different excavation sequences/stages.

1.3 Principles of Conventional Tunnelling (NATM) Depending on the project conditions (e.g. shallow soft ground tunnel, deep rock tunnel) and the results of the geotechnical measurements, the requirements for a specific support are determined. Contractual arrangements must be flexible to ensure that the most economical type and amount of support is used. The typical support elements in NATM are shotcrete and rock dowels. Steel ribs or lattice girders provide limited early support before the shotcrete hardens and ensure correct profile geometry. If ground conditions require support at or ahead of the excavation face, face dowels, shotcrete, spiles or pipe canopies are installed as required.

The excavation cross-section is subdivided into top heading, bench and invert depending on both ground conditions and logistical requirements (i.e. to facilitate the use of standard plant and machinery). Side drift galleries are provided to limit the size of large excavation faces and surface settlements.

Conventional tunnelling (NATM) in connection with the wide variety of auxiliary construction methods enables to achieve safe and economic tunnel construction even in situations with changing or unforeseen ground conditions. It allows reacting in both directions depending on the ground either changing to the less favourable or towards the more favourable side. This flexibility makes Conventional tunnelling (NATM) the most advantageous tunnelling method in many projects.

Using the standard set of equipment the following changes can easily be applied during construction if ground conditions change or if monitoring results require action: The Bridge and Structural Engineer

In case exceptional ground conditions encountered regardless of whether predicted or not the Conventional tunnelling (NATM) method can react with a variety of auxiliary construction technologies like: Grouting: consolidation grouting, fissure grouting, pressure grouting, compensation grouting; Technologies to stabilize and improve the ground ahead of the actual tunnel face like forepoling, pipe umbrella, horizontal jet grouting, ground freezing etc.

Conventional tunnelling (NATM) enables: 9

A greater variability of the shapes.

9

Better knowledge of the ground by using systematic exploratory drillings at tunnel level ahead of the face.

9

Greater variability in the choice of excavation methods according to the ground conditions.

9

Greater variability in the choice of excavation sequences according to the ground conditions.

9

Easier optimisation of the primary support using the observational method in special cases.

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9

A greater variability in the choice of auxiliary construction methods according to the ground conditions.

Conventional tunnelling (NATM) is especially convenient for: 9

Difficult ground with highly variable ground conditions.

9

Projects with highly variable shapes of cross section.

9

Projects with a higher risk of water inflow under high pressure.

9

Projects with difficult access.

9

Short tunnels.

Conventional tunnelling (NATM) in the context of this report means the construction of underground openings of any shape with cyclic construction process of Excavation by using drill and blast methods or mechanical excavators followed by Mucking.

1.4 Placement of the primary support elements The purpose of the primary support is to stabilize the underground opening until the final lining is installed.

In many cases it may become necessary to apply the support system in combination with auxiliary constructional measures.

The most common elements for the primary support are: 9

Rock bolts;

9

Shotcrete (plain/ reinforced with fibres or wire mesh);

9

Steel ribs or lattice girders;

9

Wire mesh;

9

Lagging;

9

Sprayed or cast in situ concrete, not reinforced or reinforced with wire mesh fibres

These elements are applied individually or in combination in different types of support depending on the assessment of ground conditions by the responsible site engineers and by taking into account the corresponding design. In each round, elements of the primary support have to be placed up to the excavation face for reasons of safety and health and according to the structural analysis and the assessment of the actual ground conditions.

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2.

Construction Methodology

2.1 General The following construction methodology describes excavation and initial support (primary lining) installation for Tunnel. All tunnels will be constructed using the NATM with sequential excavations and sprayed concrete support. Primary lining includes sprayed concrete, meshes, rockbolts, lattice girders and spiles for weaker areas. Utilization of particular support measures depends on Excavation and Support Classes. Excavation and Support Classes are basic principle of NATM and they allow accommodating required support for encountered geology. An applied support should be both safe and economic.

Secondary lining will be generated from in-situ cast concrete. Primary and secondary lining will be separated by sheet membrane providing water tightness.

2.2 Excavation method The excavation methods for Conventional tunneling (NATM) are: 9

Drilling and blasting, mainly applied in hard rock ground conditions;

9

Mechanically supported excavation mainly used in soft ground and in weak rock conditions (using road headers, excavators with shovels, rippers, hydraulic breakers etc.)

Both excavation methods can be used in the same project in cases with a broad variation of ground conditions. In both excavation methods the excavation is carried out step by step in rounds. The round length generally varies from 4 m in good conditions to 1 m or less in soil and poor ground conditions (e.g. squeezing rock). The round length is the most important factor for the determination of the advance speed.

2.3 Excavation Sequence and machinery An excavation will be done using drilling and blasting technique, weaker areas can be excavated using excavator or road header. Drilling pattern depends on many factors (geology, explosives used, required precision) and has to be prepared by competent expert and adjusted for each next round based on previous results and experience. Spoil/muck (excavated material) will be removed from tunnels using loaders

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and dumpers. Alternatively belt conveyor can be employed. Tunnel face will be divided into Top Heading and Bench, invert excavation is required only in worst geology and based on logistics. Advance length and details of applied support depends on Excavation and Support Class and can be adjusted according to actual behavior of excavation/support rock mass system.

Construction cycle for one Top Heading advance will be following: 1.

Tunnel face drilling, machine with several booms can be employed to speed up realization;

2.

After Face excavation for one round Spoil/muck removal using loaders and dumpers;

3.

Cleaning of excavated surfaces, removal of loose rocks;

4.

Spraying of seal layer on the tunnel face and excavated round (foreseen only in worst geology);

5.

Installation of external wire meshes (overlapping of meshes required);

6.

Lattice girder installation (position of joints to be controlled by survey);

7.

Drilling/hammering of fore poling bars/ spiles (foreseen only in worst geology);

8.

Spraying of the first layer of primary lining;

9.

Installation of rock bolts, (drilling of holes, installation of rockbolts, grouting);

10. Installation of internal wire meshes (if any), overlapping of meshes required; 11. Spraying of the second layer of primary lining (if any) final thickness depends on Excavation and Support Class.

Construction cycle for Bench will be the same as for Top Heading. The distance between Bench face and Top Heading face should be dependent on geology and behaviour of excavation/ support system.

individual excavation-steps/rounds, which depends on the stand-up time of the ground without support. In good ground conditions the maximum round length is limited by the acceptable tolerance for overbreak, which is mainly an economic criterion when overbreak has to be filled up to the design line of the tunnel circumference. Both excavation types (full-face and the partial excavation) allow exploratory drillings from the face at any time.

Full-face excavation is used for smaller cross sections and in good ground conditions with long stand-up times.

Partial excavation is mainly used for big cross sections in soils and unfavorable ground conditions. There are several types of partial excavation such as top heading, bench-and invert-excavation, side drifts, pilot tunnel, etc. Partial excavation shows the combination of different excavation methods in the same cross section, e.g. blasting in the top heading and excavating the bench by using a mechanical excavator. The choice of full-face or partial excavation not only depends on ground properties but also on environmental aspects, on the magnitude of settlements at the surface and economic considerations. In special cases both excavation sequences can be used. However, frequent changes in the type of excavation are uneconomical.

3.

Auxiliary Construction Measures

3.1 General In special cases, the excavation work can only be carried out by means of additional auxiliary construction measures. The auxiliary construction measures can be classified in the following categories: 9

Ground Improvement

9

Dewatering and Drainage

9

Ground reinforcement

3.2 Ground improvement Ground improvement means the application of methods that improve the mechanical or hydraulic properties of the ground.

2.4 Excavation Category

The main ground improvement methods are:

Conventional tunneling (NATM) allows full-face and partial excavation of the tunnel cross section. Besides the structural analysis, an important criterion for selecting the adequate excavation is the length of

9

Grouting

9

Jet grouting

9

Ground freezing

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Ground improvement is normally carried out alternately to the excavation and leads to interruptions of the excavation work. In special cases ground improvement can be carried out from the surface or pilot tunnels outside the future tunnel cross section.

3.3 Ground Reinforcement Ground reinforcement involves the application of methods that use the insertion of structural elements with one predominant dimension. Bolts, anchors, micro piles and spiles are such elements. The main methods of application are: 9

Pipe umbrellas

9

Face bolting or radial bolting from a pilot bore.

3.4 Dewatering and drainage In some cases the tunnel construction is only possible with the application of special dewatering measures.

According to the ground conditions and other boundary conditions conventional vertical or horizontal wells or vacuum drains can be used. In the design of the dewatering measures environmental aspects have to be considered, such as limits on lowering the ground water table, settlements, etc.

In the case of low overburden, dewatering measures can be carried out from the ground surface. In the other cases, dewatering has to be done from the tunnel cross section or from pilot tunnels.

4.

Instrumentation Interpretation

Monitoring

and provides guidelines for evaluation and interpretation of monitoring for an observational design approach as it will be applied during the execution of the works. This tunnel shall be constructed according to NATM; therefore the observational approach shall be seen as an integral part of the design.

The design should provide a framework for fast reaction and design adaptations on site in accordance with the conditions encountered on site, thus providing an economical and safe design. Consequently, the design process shall continue on site during execution of the works on the basis of evaluation and interpretation of various monitoring results. To allow successful implementation of the observational approach on site, the following requirements have to be met: 1)

Framework Design, providing the flexibility required on site (for example “standard design” to be applied plus “auxiliary measures” to be applied according to the encountered conditions);

2)

Organizational Structure on site allowing a fast decision making process;

3)

Extensive monitoring program providing the input information required for decisions. It is essential that the same person is responsible for the supervision of all instrumentation monitoring works.

4)

Experienced personnel on site capable of interpreting and evaluating the monitoring results and providing proper guidance during the construction process.

5)

Acceptance and support of all involved parties for the requirements of daily monitoring activities.

and

4.1 General Critical requirements of any instrument are reliability and providing easy and fast installation, operation and calibration. The instruments shall be durable and not prone to damage during and after installation.

In the case of electrical readout devices and electrical remote reading facilities, the reliability of the measured signals shall be such that the instrument’s accuracy fulfils the short term as well as the long term requirements under the prevailing environmental conditions underground with cable lengths of more than 250 m.

The device shall be designed to deliver stable electrical signals during the intended service life of the instrument. This document addresses the methodology

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Fig. 1: Pavement Marker

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4.2.3 Targets or Reflectors With absolute displacement monitoring it is possible to determine 3D-coordinates of defined targets (reflectors) fixed to the tunnel lining or other points of interest. This information is used to track the target movements with time and allows a realistic assessment of the deformation behaviour of the tunnel. Layout of monitoring stations respectively their spacing between each other is depending on the geological conditions and the sensitivity regarding deformations of the respective area.

Fig 2: Ground Marker

4.2 Instrument Specifications 4.2.1 Level Points Whereas three-dimensional deformation is most interesting in underground structures, simple settlement monitoring is usually sufficient for the assessment of the surface deformation. At a larger scale it is also more efficient due to the speed of instrument installation and reading. Several types of markers are to be used according to the nature of the monitored structure: 4.2.2 Convergence Bolts 1)

2) 3)

Convergence bolts or pins shall consist of ribbed bars protected against corrosion with a minimum length of 250 mm.

The pins shall be securely attached to the exposed rock or shotcrete surface.

After installation, the convergence pins shall be protected by a protective cap.

Fig. 4: Prism Fig. 3: Bitargets on with bolt reflex targets

Fig.5: Theodolite

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Fig. 6: Theodolite

Whereas bireflex targets are usually sufficient for underground deformation monitoring, prisms are used for fully automated real time monitoring.

4.2.4 Theodolite Opto-electronical Theodolite with integrated coaxial electronic distance meter (EDM) shall be used. The equipment shall ensure an accuracy of 3cc for directions as well as an accuracy of Âą 0.1 mm for distances.

Fig. 7: Placement of theodolite at reference point for readings

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The measuring arrangement shall include further equipment as follows:

waterproof, suitable for rough environment near the excavation area at the tunnel face. Cabling shall withstand shotcreting.

a)

Illuminated 4-line matrix display

b)

Numeric and alphanumeric input options

Mechanical dial gauge with calibration standard for initial readings can be used.

c)

Plug-in data recording module with 2000 data blocks

4.2.6 Strain Gauges (Strain Meters)

The theodolite shall be maintained to above accuracies throughout the contract period.

4.2.5 Borehole Extensometer Borehole extensometers shall be of multiple position type. The minimum lengths of anchor parts shall be 500 mm with a minimum diameter of 20 mm. Each rod shall be protected by a waterproof tube to be able to move freely. The diameter of the borehole for installation of the extensometers depends on the type (single/multiple rod type) and it shall be in accordance with the manufacturer’s recommendations.

Provide resistance type strain gauges, or equivalent, with the following minimum requirements.

1)

Maximum strain range, 10*10-3 m/m for compression, 4*10-3 m/m for tension

2)

Accuracy of least 10-5 m/m

3)

Average sensitivity, one microstrain

4)

Temperature range, -10°C to +60°C

5)

Active gauge length, 200 mm minimum

6)

Electrical cable, shielded and rubber insulated

7)

Optional thermistors shall be furnished with strain gauges and shall be incorporated with strain gauge in the same instrument.

Fig. 9: Strain Gauge

Fig. 8: Borehole Extensometer

Multiple rod type extensometers shall be designed to read at least three positions spaced as defined on the drawings. The instruments shall be corrosion resistant.

The dial gauge stop shall be adjustable to ± 100 mm.

Initial readings shall be taken by a dial gauge with calibration standard. Following measurements can be taken remotely by using electrical transducers. These sensors shall have a measuring range of 50 mm and shall guarantee an accuracy of the extensometer readings better than 0.05 mm. The sensor element shall be equipped with a 4-20 mA interface to ensure a data transmission without loss of information. The replaceable sensors shall be robust, stainless and

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Waterproof shielded electrical cable resistant to shotcreteting and water shall be provided.

4.2.7 Radial Pressure Cell Pressure cell should comply with following general requirements: a)

Sensitivity: 0.2% of full scale

b)

Measuring range of electrical sensor: 5 MPa

c)

Total System Accuracy: ± 2% of full scale

d)

Active measuring area: 300x300 mm

Couplers shall be provided for mounting cells onto protective wire mesh lining.

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Fig. 10: Pressure cell

Fig. 12: Standpipe

Instead of a simple re-pressuring device the flat jack shall be equipped with devices for re-grouting the gap between pad and shotcrete/concrete which might appear due to shrinkage of shotcrete/concrete.

The sensor shall be equipped with an output interface (4-20 mA or VW), suitable to transmit data without loss of accuracy due to long cabling. Provide shielded cable or tube for connection to terminal panel.

4.2.8 Borehole Piezometer Piezometers are used to measure pore water pressure and will be installed within boreholes with a maximum length of 30 m in all directions.

Where groundwater fluctuation is expected and has to be monitored accordingly, different types of piezometers have to be installed according to the application purpose. Examples are given below:

Fig. 13: Water Level Indicator

h)

Maximum diameter of the borehole (measuring diameter): 80 mm

i)

Electrical cable: shielded, and rubber insulated

4.3 General Procedure

The equipment shall comply with following general requirements:

In general, the data handling and information flow of monitoring results shall be as follows:

e)

Sensitivity of sensor: 0.1% of full range

1)

f)

Accuracy: 1% of full range

g)

Measuring range: as instructed by the DDC, 5 MPa max.

Upon completion of daily monitoring activities and pre-processing of monitoring raw data a preliminary evaluation of the monitoring results by a plausibility check shall be performed. Only after the results have to be found reasonable and eventual errors have been excluded and corrected, an update of the database shall be performed.

2)

When the database has been updated with the actual monitoring results, data shall be sent for evaluation and interpretation. To guarantee a quick decision with regards to support requirements and working procedures database shall be updated with the daily measurements by every afternoon.

Fig. 11: Vibrating Wire

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Fig. 14: Schematic Time- Displacement Diagram (Settlement for Crown Point)

4.3.1 Time â&#x20AC;&#x201C; Displacement Diagrams and Magnitude of Displacements Time-Displacement diagrams show the development of the displacement of one point versus time. These diagrams can be generated for all three components of the displacement vector (vertical, horizontal and longitudinal).

It is essential to consider that the displacements monitored in the tunnel are only a part of the total amount of displacements occurring. Fig. 15, 16 shows a principle sketch of the total vertical displacements and the measurable amount of displacements in the tunnel. A certain amount of pre-deformation occurs ahead of the phase. When excavation reaches the chainage of proposed monitoring section, additional part of the total displacement cannot be measured due to the time required between excavation, installation of the monitoring section and the following zero reading of the section. Therefore, it is essential that installation and zero reading of monitoring sections are performed as fast as possible without any unnecessary delays.

In this respect, all zero readings in the tunnels shall be taken within 6 hours of excavation of the relevant monitoring section.

Construction phases (top heading, bench, and invert) are usually shown on the same diagram to allow for an easy correlation between displacement behaviour and construction activities.

When a constant face advance rate is assumed, the displacement rate over time has to decrease continuously. Any acceleration indicates a destabilization, unless construction activities in the vicinity of the monitored tunnel section such as bench or invert excavation are ongoing. Usually after each excavation step a tendency towards stabilization shall occur.

Fig. 16: Schematic Time- Displacement Diagram (Settlement for Crown Point)

4.3.2 Distribution of Displacements in Vector Diagrams Displacement Vector plots allow the representation of the cross sectional displacements and their development with time.

Fig. 15: Schematic Representations of PreDisplacements and Monitored Displacements in Tunnelling

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These plots allow the detection of weak zones and / or faults outside the excavation area. They provide additional information about the rock mass structure and deformation phenomena close to the tunnel. In general, the displacement vector orientation in cross

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show the settlement of the crown resulting from top heading excavation. The uniform shape of lines corresponding to excavation steps 1 to 7 reflect a homogeneous ground mass with uniform behaviour. As the excavation approaches the fault (9) in excavation step 8, a significant deviation of the previously uniform behaviour can be observed, extending significantly behind the phase and for the duration of tunnelling through the fault further increase in settlements are measured.

9 Fig. 17: Vector Diagram – Influence in homogeneous ground Stratification

Trend Lines- Trend lines are generated by connecting settlement values of individual lines of influence at a predefined distance behind the face. They give a good overview of the displacement development along the tunnel and are quite useful for extrapolation of the displacement behaviour ahead of the excavation face. Trend lines which show increasing displacement can indicate critical situations and shall be considered as a serious warning signal.

Fig. 18: Example for displacement vector diagram

section reflects the influence of geological structures on the deformation behaviour sub parallel to the tunnel.

4.3.3 Lines of Influence Lines of Influence are produced by connecting displacement values number of monitoring points along the tunnel axis at the same time, of a similar to a “deflection curve”. Normally, a number of lines for a specified time span are shown on one plot. In addition, construction phases (top heading, bench, and invert) are shown to allow for an immediate correlation between measured displacements and construction activities.

9

Development of Lines of Influence when Excavation approaches a “weak zone” - The lines of influence in the simplified diagram above

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Fig. 19: Development of Lines of Influence showing the increased displacements in the fault zone

4.4 Monitoring Sections for Tunnel A detailed assessment of the settlement during tunnelling process is carried out along the tunnel alignment. Accordingly, the instrumentation and monitoring scheme can be designed. The tunnelling stretch will be monitored by Standard and Main Monitoring Cross Sections. Locations and distances may vary due to the actual geological conditions and the monitored deformations and shall be decided by the geotechnical engineers of the contractor and the engineer. Tunnel instrumentation includes mainly deformation monitoring instruments (3D targets, strain meters, extensometer). In principle, there are three Vol. 48 | Number 4 | December, 2018

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types of monitoring sections according to the geological and geotechnical requirements.

for adjustment of excavation and support procedures and/or monitoring shall be considered.

4.6.2 Alarm Level The Alarm level relates to threshold values on accidence of which the element of work may be approaching a critical state. The IE shall convene for judgment of the specific case and the overall support and rock mass performance. Implementation of additional support and / or contingency measures to avoid the accidence of the Action Level shall be considered.

4.6.3 Action Level

Fig. 20: Trend lines are generated by connecting settlement values of individual lines of influence at a predefined distance behind the face

4.5 Control Limits Comparison of monitoring data with control limits will give a first indication for the identification of potential areas which are close to or exceeding design limits.

This level relates to threshold values on accidence of which the element of work is considered to be outside the expected range of assessed behaviour and may be close to its ultimate limit capacity.

The overall performance shall be rechecked along with a related risk assessment. A design review shall be performed together with an assessment of the need for additional support. Additional support and/or contingency measures to guarantee the safety of the works shall be implemented.

For the judgment of rock mass behaviour and performance of the primary support, control limits are established in terms of primary lining displacements, displacement velocities, shotcrete strains, settlements etc.

In case of any unacceptable safety risk, the works shall be stopped and remedial measures shall be implemented immediately.

4.6 Types of Control Limits

Control limits shall be defined by the IE for the following monitoring parameters:

Under expected construction conditions the monitored displacements and other monitored data will be below the established threshold values, called control limits, which define certain design limitations.

4.7 Defined Monitoring Parameters

9

Displacement velocities derived from 3D absolute displacement monitoring

9

Differential Settlements

The control limits are established by the following trigger levels.

4.6.1 Alert Level The alert level relates to threshold values representing the assessed behaviour (predicted values), on accidence of which certain routines will be started to impose an increased attention and surveillance to these specific areas.

The alert values indicate that the specific area is approaching a level where additional actions and/or contingency measures may be necessary. The need

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Fig. 21: Definitions of Control Limits for Displacement Velocities

The Bridge and Structural Engineer

9

Shotcrete strains derived from strain measurements with shotcrete strain meters in the shotcrete lining

Information’s derived from other monitoring results such as extensometers, ground pressure cells etc. are used to confirm and supplement monitoring data and trends derived from the instruments mentioned above and to judge the overall performance and safety of the construction in case of accidence of control limits.

The definition of control limits shall be considered as flexible and adjustable, which means control limits shall be updated regularly, if necessary. The control limits shall be adjusted on basis of experience gained during construction, if required.

4.7.1 Displacement Velocity

Control Limit

Limiting Value (mm/mm)

Alert

10 -3

Alarm

5 ×10-5

Action

10 -2

As a guideline, the control limits related to measured displacement velocities are defined as follows: 4.7.2 Differential Settlements Top Heading Crown – Top Heading Footing Table 3: Control Limits for Trend Lines

Displacement velocities are calculated from the measured 3D optical displacements and are an important indicator for stability development. Usually, time intervals between observation points “tn” are taken as one day. However, if the elimination of scatter effects related to monitoring inaccuracies is required, larger time intervals may occasionally be applied? It is assumed that progress in the top heading will be 2 – 3 m per day.

Table 1: Control Limits for Displacement Velocities Control Limit

Table 2: Control Limits for Differential Settlements Top Heading Crown – Top Heading Footing

Displacement Velocity

Control Limit

Differential Settlement (mm)

Alert

+5

Alarm

+1

Action

-3

Differential Settlements between the top heading crown and the top heading footing shall be monitored to identify potential instabilities at the shotcrete lining footing: Table 4: Control Limits for Strains in Shotcrete Lining

Alert

vn = 0.8 v n-1

Control Limit

Alarm

vn = 1.0 v n-1

Alert

0.2

Action

vn = 1.1 v n-1

Alarm

0.4

Action

0.6

Increase in displacement velocity indicates that the rock mass is not stable and may be indicative for progressive destabilization.

However, immediately after excavation an increase of displacement velocities is an expected phenomenon caused by stress redistribution. After installation of the primary support, these displacement velocities shall decrease and stabilize after the excavation phase has advanced further and the stress redistribution is completed.

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Differential Settlement: ΔΣ = S

Strain [%]

–S crown

footing

Control Limits for trend lines are defined in terms of δ ––––––– With advance δ = Increase in displacement advance = corresponding phase advance

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4.7.3 Shotcrete Lining Strains: Refer Table 4 5.

Discussion and Conclusion

The instrumentation and monitoring system is designed to provide the following information: 9

Observation of ground behaviour and groundstructure-interaction

9

Verification of design for both the temporary and permanent works

9

Comparison of predicted and actual movements

9

Early warning of ground movements and potential damages

9

Contingency measures and trigger levels

In general it is proposed to establish monitoring array locations between 20 metre and 50 meters along the alignment. However, there may be restrictions on the

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type and location of instrumentation. However, the instrumentation scheme can be adopted during execution of the works due to the change in geological conditions or construction.

6.

References

1.

Austrian Society for Geomechanics: Geotechnical Design of Underground Structures with Cyclic Driving

2.

Austrian Society for Geomechanics: Geotechnical Design of Underground Structures with Continuous Driving

3.

ON B2203-1:2001 Underground Works â&#x20AC;&#x201C; Work Contract, Part 1: Cyclic Driving (conventional tunnelling)

4.

ON B2203-2:2001 Underground Works â&#x20AC;&#x201C; Work Contract, Part 1: Continuous Driving (mechanised tunnelling)

The Bridge and Structural Engineer

EFFECT OF CONSTRUCTION OF UG CORRIDOR & STATIONS ON INFLUENCE ZONE OF EXISTING STRUCTURES

Dr. B C ROY

Tanmoy GUHA

BCE, M.Tech (Struct), Ph.D MD, RUPL B C Roy, FNAE, Ph.D, M.Tech (Struct.), BCE. In a career spanning over 45 years in Civil/Structural engineering, Dr. Roy has dealt with many multi-disciplinary projects; experience ranging from developing concept plan to execution and has adopted innovative techniques in his designs. He was Chief Engineer for part of Kolkata NS Metro, FIRST Indian Metro and PD/JPD for EW Metro passing under River Hooghly. He is a Fellow/Member of many professional associations of repute.

Abstract Todayâ&#x20AC;&#x2122;s major challenge is to provide connectivity and promote growth by providing adequate inputs to the infrastructure which would improve the quality of life of the residents. For an underground transport facility, however, the demands are not being satisfied with the conventional processes and procedures and thinking out of the box has become necessary. The ideas behind conventional top-down and bottom-up construction have to be revisited to accommodate the current realities of restricted space available in congested corridors, noise pollution, faster construction etc.

Construction of underground corridors, stations and shafts could lead to ground movement and displacement depending upon depth and volume of works underground, soil conditions and type of foundations of existing buildings and utilities.

Indian urban cities like Kolkata, Mumbai and Delhi are old and historic cities consisting of many structures including old and new heritage structures and some of them were encountered in the alignment of a The Bridge and Structural Engineer

B.Sc, B.E. (Civil), MBA DGM, Jacobs -CES Guha, T, born Feb 1964, has 29 years of experience in planning, construction supervision, quality control and assurance in civil structural projects particularly in Metro, transport and urban structures and oil & gas sector.

number of Metro Projects like East West Metro (EW) Project, Kolkata that required detailed planning of retrofitting measures and monitoring during the construction activities. The considerations included intermodal connections to new metro station with existing Terminals like Howrah & Sealdah in Kolkata, Mumbai Central, CST in Mumbai. It also included the assessment of impact on heritage structures affected by the elevated alignment and any archeological impact of the construction for the underground stations.

Key Words: Kolkata North-South (NS) Metro, East West (EW) Metro Kolkata, Heritage Structures, Structural Listing, Condition Assessment, Ground Settlement, Instrumentation & Monitoring Introduction Underground Corridor Metros (also for road ways) are in general planned to be made of Precast Concrete Segmental Tunnel, while Stations & shafts are planned to be constructed using Cut & Cover approach, either using Top â&#x20AC;&#x201C; Down or Bottom - Up depending upon site condition. In thickly built up areas NATM Vol. 48 | Number 4 | December, 2018

97

approach may also be used. Accordingly it is anticipated that the selection and proper use of Tunneling method appropriate to the sub surface conditions encountered is good to control ground movements. If required, additional protection needs to be applied to avoid damage to the existing structures.

The paper covers.

1.

List of structures within the influence zone

2.

Structure Condition Survey

3.

Vulnerability Assessment

4.

Structural Audit

5.

Protective works and Supporting Structures

6.

Assessment of Ground movement and associated risk

7.

Instrumentation and Monitoring.

Fig.1: TBM Tunnel

Geology Geotechnical assessment of the alignment of Project corridor is required to determine the geophysical profile of the soil. For the soil type in the corridor, data may be correlated with strength and stiffness parameters to N values. In addition ground water level along the corridor is to be determined and depending upon the conditions below ground type tunnel construction could be planned.

The details are important for calculating volume loss and also to predict settlement. The geotechnical indicates mixed face ground conditions and during construction the interface needs to establish as accurate as possible, to take greater precautions during tunneling and excavation, to avoid excessive ground movement/collapse. Ground pre -treatment in certain areas, may be decided as/if required.

Fig 2: Cut & Cover

Existing Structures Protection Program The major portion of the Metro alignments in India passes through the densely populated/ thickly built up areas. Metro Construction has two major components. â&#x20AC;˘

98

Corridor as underground Tunnel (using TBM or Cut & Cover) and Stations being built by Cut & Cover system use top down/bottom up construction approach. Shafts are in general proposed to be built using bottom up approach.

Ref Fig.

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Fig.3: Bottom-up condition of base slab

The Bridge and Structural Engineer

•

Majority of structures within the zone of influence of tunneling, it can be anticipated that the selection and proper use of a tunneling method appropriate to the surface conditions encountered if not sufficient to control ground movements then additional protection may be necessary.

The induced ground movement and Ground water draw down during tunnel excavation are major considerations. Accordingly selection of Tunneling method is very important. In general Shield Tunnel Boring Machine (TBM) and precast reinforced concrete linings are preferred options to give the final shape to the Tunnel Corridors.

Accordingly issues need to be studied for the type of Structure is: 1. Nature and variability of ground conditions 2. Construction impact like noise, vibration and ground movement, particularly to satisfy stringent control for Heritage Structures 3. Impact on all structures 4. Effect of ground movement due to tunneling / excavation operation.

5. Monitoring actual ground movements, including settlement, angular distortion, crack width measurement within the influence zone 6. Damage assessment based on type of foundation, type of Structures, condition of building / structure.

Investigation is required for the performance of deep excavation and the associated effect on the adjacent buildings and existing utilities. Field observations include deflection of Diaphragm walls or otherwise, vertical movements at wall top, ground settlement and settlement of surrounding buildings and utilities.

3.

Possible control of development of stresses

4.

Progressive deformations

5.

Supplement if any important data of existing buildings are missing

6.

Protect structures by underpinning, jacking, isolation, grouting or other means

Ground Movement Assessments In order to control the risk of damage, assessments are to be undertaken for existing infrastructure including buildings within the zone potentially affected by ground movement. It is routine part of the tunnel and infrastructure design process and involves using well established methods to assess the need for any mitigation measures. The process aims to identify systematically any infrastructure which is at significant damage risk and to quantify the level of that risk.

Infrastructure at very low risk need to be identified and discounted from more detailed assessment .Three phase assessment as discussed below may be undertaken.

The basic objective is to determine the level of damage risk to old and existing structures on the alignment to enable planning of ground movement, necessary monitoring and risk mitigation measures like defect surveys. The designed methods identify existing buildings at greater risk focusing on subsequent activities.

Phase 1 •

•

Over excavation and long construction duration causes the shoring/load bearing walls to develop substantial deflections. Base and middle floor slabs play prominent role in reducing post excavation deflection and settlement.

Precautions 1. Verification of appropriateness of the selected Tunneling method 2. Method of control of settlement at surface, requiring additional protection like freezing, grouting or underpinning The Bridge and Structural Engineer

•

•

This phase assumes a “green-field” site condition meaning that the effect of building foundations and other infrastructure is ignored for the purposes of assessment on the pattern of movement.

For bored tunnels the settlement predictions for “green-field” site conditions are based on empirically validated methods using parameters for ground loss determined from various case studies taking into account the method of tunneling and ground conditions.

For excavations comprising deep shafts, boxes and retained cuttings, assessments can be done using models validated by empirical data based on case studies of similar excavations.

If the predicted settlement from bored tunnels and from the excavations exceeds 10mm, further assessments of the buildings are required.

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99

Phase 2 • Initially the buildings are subjected to conservative approach i.e. they are assumed to behave flexibly having no influence on movement behavior due to their stiffness

•

Buildings assessed in terms of risk categories are identified based on sensitivity of the structure to ground movements and interaction with adjacent buildings

Table 1 : Building Damage Category Classification Risk Category

Max Tensile Strain %

Description of Degree of Damage

Damage and Likely Form of Repair for Typical Masonry buildings Description of Typical

Approx. Crack Width (mm)

0 1

0.05 or less > 0.05 and < 0.075

Negligible Very Slight

0.1 to 1 1 to 5

2

> 0.075 and < 0.15

Slight

3

> 0.15 and < 0.3

Moderate

Hairline cracks.

Fine cracks easily treated during normal redecorations.

Perhaps isolated slight fracture in building. Cracks in exterior brickwork visible upon close inspection.

Cracks easily filled. Redecoration probably required.

Several slight fractures inside building. Exterior cracks visible; some repointing may be required for weathertightness. Doors and windows may stick slightly.

Cracks may require cutting out and patching. Recurrent cracks can be masked by suitable linings. Repointing and possibly replacement of a small amount of exterior brickwork may be required. Doors and windows sticking.

Utility services may be interrupted. Weather tightness often impaired.

4

> 0.3

Severe

Extensive repair involving removal and replacement of sections of walls, especially over doors and windows required. Windows and door frames distorted. Floor slopes noticeably. Walls lean or bulge noticeably, some loss of bearing in beams. Utility services disrupted.

Usually greater than 25 & also depend on number of cracks

Very Severe

Major repair required involving partial or complete reconstruction. Beams lose bearing; walls lean badly and require shoring. Windows broken by distortion.

Danger of instability.

5

Buildings under risk category 0, 1 or 2 are not subject to further assessment while buildings under risk category 3 or more are further required to be assessed as in phase 3 Phase 3 •

In Phase 3 of the assessment procedure, each building is considered individually that include building specific detail model rather than the more generic model form.

•

It is also adopted if it is on shallow foundations and is within a distance from a retained cutting, shaft or box equal to the excavated depth of superficial deposits. In this context, superficial deposits are taken to be soils such as Made Ground, Alluvium or Terrace Gravels,

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•

5 to 15 or a number of cracks greater than 3 15 to 25 but also depend on number of cracks

It is a listed building and/or whether protective works for the buildings are required

Structures listing including Heritage Structures within the influence zone This section details on Condition Surveys, Settlement & Damage Assessment for East-West (EW) Metro Project, Kolkata. The structures and buildings surveyed within the influence zone had 430 existing Structures buildings and structures that included Heritage structures along the alignment of the Metro Project was categorized into five separate divisions as mentioned in the aforesaid risk categories and also according to their extent of damages by visual observation, age, frequency of maintenance undertaken by the owners/ occupants etc. and were listed under the following heads as shown in the Table.

The Bridge and Structural Engineer

Table 2 : Status of Structural Buildings in Influence Zone Type

Status

Total

U/C Good Average Bad

Vulnerable

G+0

0

9

14

3

1

27

G+1

0

13

39

53

10

115

G+2

2

17

32

30

7

88

G+3

1

27

17

32

1

78

G+4

1

25

8

9

0

43

G+5

1

19

7

4

0

31

G+6

0

5

3

1

0

9

G+7

0

5

2

1

0

8

G+8

0

1

1

1

0

3

G+9

0

3

1

1

0

5

G+10

0

2

0

2

0

4

Water Tank

0

0

1

0

0

1

Total

5

126

125

137

19

412

i) ii)

iii)

iv)

v)

Under Construction (UC) – Some Buildings were under construction.

Good – Buildings having sound health with minimum damages in the form of dampness, minor cracks in plaster and in auxiliary columns, chajjas, very small plants which can be uprooted during routine maintenance work.

Average – Buildings having medium type of damages like cracks, spalling of plaster from walls and slabs exposing reinforcements, damage of wall or concrete chajjas, roof slabs etc. due to growth of vegetation.

Bad – Major type of damages in the form of large cracks in walls and concrete portions, exposure of reinforcements with traces of corrosion, vegetation growth with hard roots penetrating into the walls, spalling of plasters, thus allowing rain water to seep into the mortars appearing in the buildings have been categorized as bad in nature.

Vulnerable – The buildings seem to have severe types of damages such as large to very large cracks, ill maintained, balconies/chajjas tend to collapse & are very age old in nature were termed as vulnerable.

Heritage structures are diverse and include historic buildings, monuments, gardens, cemeteries, The Bridge and Structural Engineer

landscapes and Archaeological sites, remains, ruins, monuments, public spaces and natural features.

Historic environment is not only matter of material remains but it is identity of individuals, communities and nation as a whole.

The importance of a property to the history, architecture, archaeology, engineering, culture and community is immense and attentions are required: 1) 2) 3) 4)

5)

Associations with events, activities and patterns.

Association with Important Persons Physical Characteristics of design, construction and forms.

Important information, illustrating social, economic history like terminals, town halls, clubs & markets.

Technological innovation

A Visionary team of experts, listed the record of ‘Heritage Structures’ available. This charter recommends heritage buildings and sites, classification as Grade I, II, III depending on order of Importance.

Buildings /Sites classified as Grade I and II should be considered in accordance to provisions of Officials & Legal Manuals.

Buildings identified for both Kolkata EW and Mumbai Metro include both Heritage and non-heritage Structures and a separate list of Heritage Structures was prepared.

Information on Buildings identified are: a) b) c) d)

Year of Construction Plan and Details of Buildings/ Structures Type of Structures (Foundation/ Superstructure) Major Repairs & Rehabilitation carried out in past

As drawings of most of the drawings of Buildings/ Structures are not available, Survey teams, belonging to Client or Client’s Engineer collected site data to the extent possible. It is the responsibility of the Contractors, engaged for implementation to review the list and match with actuals at site. Contractors need to check/recheck condition of Buildings and Categories based on existing damages. In categorizing the building, conditions to be surveyed based on the followings: a) b)

Distance from the Centre of the Alignment.

Method adopted during Construction.

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101

c) d) e)

Condition at the time of execution.

Detail structural examination.

Existing Condition

It is common and natural for residents of buildings to observe and attribute pre-existing condition in buildings to the effect of adjacent excavation of Stations/Shafts/ Tunnels etc.

Preconstruction photographs and Video (done for EW Metro) are important in issues obtain a history of building movements due to seasonal changes. A logical evaluation of ground movements and building distortion due to excavation or tunneling is done.

Understanding the chain of relationships and behavior extending from tunneling (both for TBM tunnel or Cut & Cover) or excavation i)

Ground movement sources and ground loss

ii)

Ground movement patterns and volume changes

iii)

Building structural Characteristics and finishes – how it was built, maintained and repaired.

viii) Verticality / Plumb of the Building to check tilt / twist. ix)

Damage of non-structural members.

Approach Methodology To assess and protect existing structures, existing & potential damages need to be worked out. This may be done based on ground movement and using Empirical and numerical analysis. For Cut & Cover sections both vertical and horizontal settlement / movements should be worked out.

Cut & Cover method is cost effective, safe, easy to control and implement. The disadvantages are: 1.

PUO pipes needs to be removed/ diverted/ or keep hanging in position keeping the system operative

2.

Archaeological issues need to be taken care

3.

Availability of sufficient land both for permanent structures & required construction area.

4.

Appropriate traffic diversion with minimum hindrances to movement

Effects may superimpose on pre-existing building condition like, cracks, distortion and deterioration. Data available are mostly inadequate and the contractors have to carry out detail building condition, building condition surveys (BCS).

Additional measures during planning, design and construction •

While carrying out BCS, the Contractor may follow items followed during initial survey (Client’s Survey) and in addition carry out any other items which are required depending on site specific requirements.

Client’s Survey for running Metro Projects include:

Adopting a relatively rigid excavation support system like diaphragm wall, instead of using sheet pile, soldier pile with laggings etc.

•

Visible Surface Cracks were recorded as nonstructural cracks and through cracks are structural.

Assessment of the probable settlement, lateral movement of the excavation support system, leading to subsequent effects in adjoining structures and determining the threshold values.

•

Pre-loading of the struts meant for holding the diaphragm walls in position.

ii)

Surrounding Ground Condition to detect subsidence or upheaval.

•

iii)

Verticality of Walls, particularly in case of load bearing, in checking bulging, deformations or any other form of distress.

Implementing a detailed Instrumentation and Monitoring Plan, including Real Time monitoring for additional safety and as a precautionary measures

•

Limiting the ground water drawdown/lowering.

iv)

Cracks at the interfaces.

v)

Critical inspection of major overhangs to detect cracks, deformation, deflection etc.

•

vi)

Spalling in RCC Structures, particularly for slab, beams & columns.

A threshold value for sensitive buildings and structures, including the protected monuments were determined at 80% of the maximum anticipated value of movement and beyond this limit, construction activity may be continued only after implementing remedial measures

i)

vii) Indication of foundation settlement.

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The Bridge and Structural Engineer

17.5m from Maghen David Synagogue, the two heritage buildings with closed collaboration with the Archeological Survey of India.

•

Instrumentation and monitoring are required to be carried out both during implementation and operation stages. To start with one has to establish base-line movement, distortion, ground water level & its fluctuation, noise and vibration, indication of excessive and undue movement of ground surrounding existing Buildings.

•

To monitor movement and deformation for design verification both for temporary and permanent structures is required. Also to monitor maximum allowable tolerances not exceeded for structures within influence zone. Water drawdown outside the excavation needs to be controlled within natural ground water fluctuation.

•

Daily monitoring of instrument readings for the entire construction period.

•

Stringent Review criteria – Alert, Action & Alarm (AAA).

•

Validate AAA-levels with predicted ground movements.

Fig. 4 : Monitoring movement and deformation using instrumentation equipments

•

Rigorous monitoring of existing structures, including the protected monuments.

Implementation, Instrumentation & Monitoring Plan

•

Implementation of mitigation measures wherever necessary.

•

Project corridor abuts a number of old and historical buildings generally in Indian Metropolis.

Instruments and purpose

•

Project implementations are to be worked out with utmost priority to minimize disturbance of traffic and existing establishments and carry out construction activities ensuring safety of works and property.

•

•

•

In most cases due to land constraint, the construction of underground station box is to be done at close proximity (as close as 1m Refer Fig) of a number of multi-storied buildings with utmost care least effecting adjacent buildings Comprehensive instrumentation scheme to be adopted for tunnel, cut & cover corridor and stations needs to be identified for major concerns.

A typical construction approach is also envisaged for Mahakaran Station (EW Metro), where the excavation is 18m from Beth-El Synagogue and

The Bridge and Structural Engineer

Instruments which are in general deployed are; Temporary Bench Mark : to monitor vertical movement.

Precise Levelling Point : monitoring of monuments Precise Levelling Studs : for installation on pavement at right angle to tunnel.

Piezometers

: monitoring of ground water level.

Inclinometers

: monitoring of lateral movement, including Diaphragm wall:

Extensometer

: to monitor vertical deformation or heave.

Strain gauges

: to monitor strains of struts, anchors etc.

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103

Load cells

: monitoring of loads at struts, anchors etc.

Tilt meter

: to monitor tilt of buildings.

Crack meter

: monitoring cracks.

Vibration

: to measure vibration of existing structures

Depending on the findings of the assessment process like cracks (Ref Fig.) the following types of mitigation measures may be undertaken during construction to protect buildings from the effects of ground movement.

Mitigation Measures Based on the outcome of the building inspections, engineers are required to allow for the condition of the building when conducting their assessment of the potential damage induced by underground construction. There is no explicit guidance on how the existing condition of a building can be classified, and this has resulted in different opinions on what types of defects would cause a building to be classified as being in a ‘satisfactory’ or ‘poor’ condition.

However this study is a brief manner dwells on defining the risk assessment criteria. The Mitigation work shall look into the structures in the influence of the work and gauge / estimate the possible damage due to the construction to ensure prevent / minimize subsidiary damages and costs. The work shall be such planned / designed so as to ensure that no damage is done to the buildings or the damage as identified in the BCS does not aggravate, while the work is been carried out. The work is definitely not for the strengthening of the buildings above, that is never the scope of the work of the underground transportation contract. The parameters shall be visually inspected or with the help of Schmidt’s Rebound hammer or maximum with Ultra sound pulse velocity equipment.

The intent of the work is to ensure that the building does not undergo any further damage during the works. Therefore minimum mitigation works is to be carried out. The inspection carried out shall include. a)

Visual inspection

b)

Carryout NDTs like Hammer and uPVC tests.

c)

Study distress and brief root cause analysis and

d)

Temporary strengthening and supporting measures.

e)

Providing instruments for monitoring the building behaviour.

f)

The analysis shall take into account the present / existing condition of building while dealing with mitigation measures.

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Fig. 5 : Different Types of Life Cracks in Structure

The Bridge and Structural Engineer

•

Minimization of ground movement at source. A range of measures used during tunneling and excavation works to reduce the magnitude of ground movements generated. The detail of the measures depended upon the type of construction involved. These include all actions taken from within the tunnel, shaft or box excavation during its construction to reduce the ground movements generated at source. ¾

¾

•

•

Many a times ground movement / vibrations cannot be reduced beyond a certain level, and certain minimum repair measures like crack treatment, extra temporary support system may have to adopted.

These measures adopted shall be mitigate propagation of distress during construction time only.

Ground treatment measures. These comprise methods of reducing or modifying the ground movements generated by tunneling/box excavation by improving or changing the engineering response of the ground. Categories of ground treatment include: compensation grouting, which involves injecting grout into the ground above the tunnel to compensate for the ground loss at the tunnel face; permeation or jet grouting which involves the creation of stiffer ground to reduce movement; and control of ground water to avoid changes which could potentially cause ground movement.

Structural measures. These methods reduce the impact of ground movements by increasing the capacity of a building to resist, modify or accommodate those movements. Typical measures would include underpinning or jacking. Underpinning involves the introduction of a new strengthened foundation system to a building or structure potentially affected by settlement. Jacking is a technique whereby a system is introduced between the building and its existing foundations to compensate for any movement.

Prevention and control measures for existing buildings at different risk levels discussed under Heritage Structures which are also applicable for all structures.

The Bridge and Structural Engineer

Effect of Transit Structure on Existing Structures during Execution and Operation Effect of Underground Metro System on the existing buildings/structures is two folds. First during execution and the other one is during operation of the system.

To find out the effect of execution of underground Metro system comprising Tunnels, Shafts & Stations and Depot one has to monitor distresses causing during the execution and superimpose the same on existing distresses, if any. During operation, in addition to monitoring new distress one has to monitor comfort and serviceability.

As per Skempton and McDonald, damage can be classified in three categories •

Architectural Damage – Affects the appearance of structures, panel walls, floors and finishes.

•

Functional Damages — Damages like jammed doors, windows, falling plaster, and dis function to utilities.

•

Structural Damage — Includes the effects on Structural, Stability & Safety.

In situ monitoring during the tunneling operation is a part of design not only for checking the structural safety and design, for verifying the basic conception of the response of ground to tunneling and effectiveness of structural support. In situ monitoring will include i)

Control deformations of Tunnel to ensure tunnel profile.

ii)

Appropriateness of selected tunneling method.

iii)

Control the Settlements at surface and to obtain formation pattern of the ground.

iv)

Monitor settlement caused by lowering water level.

v)

Development of stresses in Structural members.

vi)

Measure progressive deformation which may need ground and support strengthening.

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105

Ground Improvement, Monitoring

Protection

and

The ground control by means of the tunneling method is perhaps not sufficient to control settlements to levels that prevent functional or structural damage to structures along the alignment. For protecting buildings subject to settlements that are likely to cause damage are like Permeation grouting, Compensation grouting, Compaction grouting, Jet grouting and Underpinning.

•

Permeation grouting fills pore spaces in soil with grout.

•

Compensation grouting involves controlled injection of ground between excavations and structures need protection.

•

Compaction grouting involves injection of stiff mortar into subsurface soils in controlled manner.

•

Jet grouting, injects fluids at high pressure and flow rates in the ground.

•

Underpinning is installation of new foundations under existing building foundation.

water. Ground failure may be avoided by minimizing pore water pressure. Improvement is also possible by ground freezing and it changes the property .Time dependent stress-strain behaviour of frozen ground can be significantly different. Freezing causes an increase in water volume and heave at surface.

Fig.7: Underpinning with grouting

Construction Approach Construction approach of major elements of the Project is: On most of Transit Tunnel Projects, significant portions of the alignments are constructed beneath the Buildings.

Station boxes have been proposed to be cast in situ reinforced concrete structure. Traffic management during construction is very important .Types of Construction configuration proposed depending upon site condition, with particular reference to Station Location and its foot print. Types of Construction planned for Stations and Shafts, both for launching and retrieval, Tunnels and NATM, both for cross passage and station area where required due to site condition.

Fig. 6: Underpinning process

Grouting or injections of ground may improve ground characteristics. Though in most cases grouting is applied for closing discontinuities in rock or / and strengthening of soft ground. In addition ground is also stabilized by dewatering and by avoiding inflows of 106

Vol. 48 | Number 4 | December, 2018

In general station boxes are planned of cast-in-situ reinforced concrete.

Based on station configuration, land available or to be acquired & planned traffic management during construction, with approval of concerned authorities is very important.

The Bridge and Structural Engineer

There are two basic cut and cover construction methods, namely Top-Down and Bottom-up. Both methods are suitable for station construction. The system in principle made of temporary or permanent Retaining walls (Diaphragm wall/Contiguous bored piles or Secant Piles) including strutting system as per design requirement. However considering presence of high water level and presence of Heritage Structures Top-Down Construction will have advantage over Bottom-Up. Types of construction are as follows.

1)

2)

3)

Cut & Cover Stations in open space, either applying top-down or bottom - up depending upon compatible excavation procedure appropriate for existing geophysical condition ( In general Rock with Soil overburden).

Cut & cover Station box underneath the road wide carriageway, sufficient to accommodate the Station foot print, may be cast in situ, top down construction. However the traffic flow on the surface and also with underground utilities, will need appropriate diversion temporary or permanent depending upon existing site condition and future plan. In some areas it may need to provide temporary deck for traffic and also with temporary supports for utilities.

When type of Station is such that both item 1) & item 2) are not feasible to accommodate the full station then method using NATM may be planned.

Fig. 8 : Noise level monitored at grade above tunnel

ii)

iii) iv)

Also Noise level was monitored at grade above tunnel Conclusion The paper has tried to cover effect of underground construction on the influence zone of existing structures, risk assessment and the remedial measures and safety requirements that can be taken.

References 1.

London Underground Guidelines on Ground Movement Due to Tunneling and Deep Excavations and Non-Technical Summary

2.

Report on Condition Assessment , Monitoring and Basic Approach for Rehabilitation by B C Roy

3.

Retrofit of the Structures of Historic & Heritage Importance by Rajib Chattaraj & Bhubaneswar Koner

Construction Impact Impact during Construction, within the influenced area i)

Ground movement due to Tunneling process.

The Bridge and Structural Engineer

Ground movements, including settlement, angular distortions, and measurement of crack widths within the influence zone of tunneling operation.

Effect of Ground loss.

Effect of structure, condition of Building/ Structure.

Vol. 48 | Number 4 | December, 2018

107

ASSESSMENT OF CONCRETE DURABILITY FOR UNDERGROUND TRANSPORTATION STRUCTURES

Harshavardhan DESHPANDE

Madan MAGDUM

Civil Engineer Associate Director AECOM India. harshavardhan.deshpande@aecom.com

Chief Expert (Tunnels and Underground Structures), Louis Berger India. mamagdum@louisberger.com

Harshavardhan Deshpande, born 1970. Received his Civil Engineering Degree from NIT (REC) Calicut.

Madan Magdum, born 1979, Masters in Structural Engineering and PhD research scholar in research Centre VIIT Pune, University of Pune.

Area of Specialization: Concrete Technology and structural design for Rails, Metros, Airports, Ports, Buildings and Precast concrete structures.

Abstract Durability is one of the key parameter of the design, where the service life of transportation structure is been derived. The present available codes BS-8500, EN 206-1 and AASHTO provides guidelines based on the deemed to satisfy for not more than 100 years of service life as traditional approach i.e. based on prescribed exposure class, water cement ratio, minimum cement content and desired compressive strength. While, quantification of service life is difficult using the deemed to satisfy criteria provided in the codes. Presently, the underground structures are demanded to be designed for 120 years or higher of design service life. The model code for service life CEP-fib-34, provides guidelines more relevant based on study presenting deterioration mechanism of concrete, environmental aggressiveness, reinforcement corrosion, concrete density and diffusivity. Different approaches are provided such as Full Probabilistic Design, Semi Probabilistic and deemed to satisfy with calibrated factors and Avoidance of Deterioration over shortcomings in the traditional approach of design service life. Now a days many software are available to quantify the service life based on deterioration parameters based on Flickâ&#x20AC;&#x2122;s 108

Vol. 48 | Number 4 | December, 2018

Area of Specialisation: Concrete Technology, Design of Deep Shafts, Tunnels, Underground Metro infrastructures, Precast concrete structures.

law. This paper presents the assessment of different approaches like probabilistic approach and advantages over deemed to satisfy as traditional approach based deterioration mechanism as presented in fib34, this paper also dwells on concrete sustainability, concrete quality assurance and inspection maintenance during operation especially for underground infrastructure.

Keywords: Concrete durability, Concrete Deterioration, Quality assurance, sustainability.

1.

Introduction

There a very sharp increase in demand for delivering High Performing Concrete (HPC) with minimum need of maintenance and repairs. Major infrastructure structures like the underground structures for metro railways such as tunnel lining needs to have a good and long design life of 120 years and more primarily due to difficulty in maintenance and repairs due to heavy and busy operations. Tender specifications for these works also requires the same. Theoretically concrete is a durable material in itself, there are many old magnificent structures in the world are in excellent condition, yet it is seen that many modern and recently The Bridge and Structural Engineer

constructed structures are deteriorating fast and are not durable. It is often observed that these structures are unable to deliver good service life in aggressive environment. The critical change in the modern structure is the use of reinforcing steel embedded in concrete; the inbuilt property of concrete to change in volume due to water evaporation leads to shrinkage and creep leading to exposing the embed steel leading to rusting ruining the durability of concrete. Reinforced concrete structure is very common and popular as it enables to deliver large spans with relatively small section sizes. But the shrinkage and creep augmented with rusting of steel the durability of the structure is hampered and therefore it is imperative that to deliver durable concrete rusting of steel is prevented. Many methods are adopted are looked into be the engineers to prevent rusting of reinforcing steel and deliver durable concrete, such as use of stainless steel, galvanised steel, cathodic protection (where the entire structure is connected to rust inhibiting electric current and may not be possible many structures other than the marine structures), treatment to the concrete with rust inhibiting compounds. However none of these developments can resolve the inherent problem that putting steel inside concrete ruins its potentially great durability.

The ability of concrete to withstand the conditions for which it is designed without deterioration for a long period of years is known as durability. Capability of concrete to resist weathering action, chemical attack and abrasion while maintaining its desired engineering properties. It normally refers to the duration or life span of trouble-free performance.

Moreover durability of concrete is important as it makes the structure sustainable as less and less of concrete is used in frequent repairs and reduces carbon foot print of the structure.

2.

Salient Features to Achieve Durability

Concrete will remain durable if cement paste structure is dense and delivers low permeability; concrete is made with graded aggregate that are strong and inert.

The ingredients in the mix contain minimum impurities such as alkalis, Chlorides, sulphates and silt. Durability of Concrete depends upon the following factors o

Cement content

o

Appropriate Mix Design to achieve

Cohesion mix and segregation and bleeding is prevented.

Appropriate Cement and Water content to achieve desired workability and adequate construction chemical to achieve proper hydration without compromising the strength & durability parameters of concrete Appropriately designed Concrete mix with usage of natural aggregates Curing & Shuttering time: It is very important to permit proper strength development aid moisture retention and to ensure hydration process occur completely Adequate Cover to reinforcement

o

Permeability of concrete: It is considered the most important factor for durability. It can be noticed that higher permeability is usually caused by higher porosity. Therefore, a proper curing, appropriate cement, proper compaction and suitable concrete cover could provide a low permeability concrete.

o

Crack control: cracking occurs due to hardening of concrete in the early days after casting and due to temperature and stresses induced due to loads; crack vis-à-vis durability needs to minimised and as a good engineering practice for the underground structures the external face of concrete crack width shall be limited to 0.2 mm and the internal face crack width shall be limited to 0.3mm.

o

For the infrastructure projects design life requirement was higher than as prescribed in BS-8500, EN-206-1 and AASHTO LRFD which based on deemed to satisfy guideline for not more than 100 years of service life.

Good quality of Water proofing like the fully bonded membrane being the latest type of water proofing though shall not be considered for durability due to the reliability of water proofing related to issues related to workmanship of laying adhesion.

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

With advent of more and larger scale infrastructure projects and a desire to have a less maintenance material coupled with high strength to achieve small structural dimensions, requirement rose to develop high performance concrete was which has high durability, less maintenance during operation.

109

o

Casting of Concrete in high and low temperature vis-à-vis durability is dependent on quality control taken up while casting; the primary requirement for durable concrete is to control cracks, increase density, and to reduce porosity of concrete.

Temperature control while casting and after casting needs to be controlled to the desired degree and appropriate measures may be adopted to achieve the same.

2.1 Types of Durability There are mainly to types of the durability of concrete

3.

ii.

Alkali Silica Reaction

iii.

Alkali Carbonate Reaction

Approaches to Service Life Design / Durability

Though the causes of durability problems depend on number factors, like chloride and carbonation induced reinforcement corrosion, quality control, variation in the properties of different materials required for the compositions of concrete and depending on the properties of these material the property of concrete and concrete characteristics may differ significantly.

Concrete significantly impacts both the durability, and cost of a project, owners &engineers are constantly challenged with delivering of durable and high performance concrete.

o

Physical durability of concrete: Durability against percolation and permeability of water / chlorides and carbonation and Temperature stresses i.e. high heat of hydration

o

Chemical durability of concrete: against following actions

o

Alkali Aggregate Reaction

o

Sulphate Attack

The biggest challenge today to achieve availability of good quality natural aggregates, predominantly non availability of natural sand and dependency on artificial sand and quality issues associated with the available sand.

o

Chloride Ingress

3.1 Prescriptive - Deemed to Satisfy Approach

o

Delay Ettringite Formation

o

Corrosion of reinforcement

Internal Causes

Present design codes and standards for concrete are based on deemed to satisfy approach to the design and prescribes reinforced concrete based on exposure environments. The prescriptions given in the codes can be adopted to deliver design life of maximum 100 years. The prescribed values of maximum water cement ratio, minimum cement/ cementitious content, required compressive strength and exposure conditions are minimum requirement and may not be veracious to achieve long service life by satisfying the prescribed values given in these codes. Limitations of the codes based on prescribed and deemed to satisfy approach is that the design life is very hard to quantify i.e. predicting life of concrete is difficult. The approach is based on past observations and experiences, limited research data and based on engineering judgement.

Moreover this approach does not differentiate sufficiently with regards to actual exposure.

3.2 Probabilistic Performance- Based Approach.

2.2 Causes for the Lack of Durability in Concrete o

o

External Causes

Extreme Weathering Conditions

Extreme Temperature

Extreme Humidity

Abrasion

Electrolytic Action

Attack by a natural or industrial liquids or gases

Physical: Volume change due to difference in thermal properties of aggregates and cement paste Chemical i.

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Alkali Aggregate Reactions

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As the traditional procedures have shortcomings in assessing the design life of concrete structures; focus therefore shifted towards studying the deterioration mechanism of concrete, Corrosion of reinforcement, density of concrete, diffusivity and study of

The Bridge and Structural Engineer

probabilistic performance based durability design of concrete structures. Probabilistic and performance based service life design approach considers the probabilistic nature of environmental aggressiveness, degradation process and the properties of cement, SCM (Supplementary Cementitious Material) and aggregates. This probabilistic approach is based on similar principle as that of Ultimate Strength adopted for design i.e. the safety requirement and limit states are defined for the design service life. This approach addresses mainly chloride and carbonation ingress in concrete and the effect on reinforcement as these two parameters are often the most decisive parameters for the deterioration of concrete. The Ingress of chloride and carbonation in concrete or corrosion effect on the reinforcement can be addressed through “deterioration and transport models” estimate the time taken for corrosion commencement; this approach is performance based as the time factor of these effects are considering in determination of design life.

•

Identification and quantification of environmental exposure for different types of structural elements based on their location

•

Determination of design quality of concrete with respect to design penetrability of the aggressive substance and concentration depending on the environmental exposure.

•

Special protective measures which can form part of a multi- stage approach to durability include:

The durability design approach which is adopted in the industry and is indicated in fib Bulletin No. 34: Model Code for Service Life Design. Design activity shall be carried out with a perspective to achieve a desired level of reliability. Four level of performance based design of concrete structure is recognised.

• • •

•

A full probabilistic Design (Level-1) A partial factor (Semi Probabilistic) with factors calibrated with level-1 above A deemed to satisfy Design corresponding to methods in current codes and standards but requirements calibrated with level-1 above to the extent possible.

Avoidance of Deterioration.

Other deterioration parameters like sulphate attack, ASR (Alkali Silica Reactivity) are differently dealt by considering Avoidance of Deteriorating Approach.

Adopting good quality concrete having appropriate Fineness, Soundness, Consistency, Strength, Setting time, Heat of hydration, Loss of ignition, specific gravity and density.

Use of good quality of materials (Aggregates) i.e. grading, durability, particle shape and surface texture, abrasion resistance, absorption and surface moisture and presence of delirious material.

The use of concrete containing SCMs (i.e. fly ash, slag) at the correct replacement levels.

Protection of all materials against chloride contamination prior to concrete placement.

Limitations to alkali-silica / aggregate reactivity (ASR / AAR).

Total isolation of all exposed concrete surfaces against the ingress of chlorides during the curing period.

Specification of concrete cover with respect to chloride diffusion effect.

Proper quality control including permeability testing during trial mixes’ preparation as well as during the construction period.

Approach for Durability Assessment

•

Important point of the approach is that the probabilistic nature of the environmental aggressivity, process of degradation and material properties. Based on this the concrete cover and the concrete grade is assumed and the design life and ingress determined. Following parameters are required to assess the ingress of assess the design service life of concrete.

Design life is determined as 90% probability that no corrosion is initiated. Secondly determine the design service life for the cover provided for the reinforcement.

•

During the initiation phase chlorides penetrates through the concrete cover and approaches the reinforcement. Initiation phase ends when the chloride reaches the critical level of reinforcement threshold; this may be assumed as acceptable limits for the Service life.

4.

•

Adoption of design life and acceptance criteria and determination of nominal cover

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111

Software based on Fick’s law Initiation phase of chloride ingress and carbonation ingress representing the design life: the chlorides penetration or carbonation of concrete reaches the reinforcement. The data required to determine the time taken for ingress is as follows: •

Environmental loading; Loading (CS) / chloride or Carbonate concentration

•

Age at loading (t’)

•

Temperature (T) Ambient temperature

•

Concrete quality & cover to reinforcement

•

Reinforcement threshold (ψ)

•

Ageing factor (m)

•

Chloride diffusivity (D), deduced from RCPT and NT Build 492

•

Time dependence of the chloride diffusivity (α)

•

Critical Chloride Content (CCR)

•

2Fe(OH)2 + ½ O2 → Fe2O3·H2O + H2O (Cathodic reaction)

Chloride ingress may occurs by simple diffusion, capillary risk, water movement through the concrete or by evaporation / concentration effects. The rate of chloride ingress is dependent on the concentration in the environment and the quality of the concrete, which itself is dependent on a) Water – cement ratio, b) Cement (binder) content, c) workmanship (compaction and placement), d) quality control, e) cement and concrete additives. For the underground Structures the water table When concrete is fully submerged in water (under-ground structures with high ground water table ) chloride ingress may occur due to diffusion but will be slow Where the concrete is fully immersed in the groundwater (tunnels), although chloride ingress will occur but (due to diffusion) will be slow due to lack of oxygen.

Extent of conventional corrosion will be limited by the lack of oxygen.The rate ofingress for concrete approximately depends on concentration being inversely proportional to depth of reinforcement and the square root of the exposure time. Figure below shows the relationship of the critical threshold limit to the concreteenvironment.

CLcount total =in wt. % of binder

Fig. 1: Service Life of Concrete Structures- time related modelling of deterioration- initiation and propagation

4.1 Reinforcement Corrosion Due to Chloride Ingress Chloride ions will reach steel reinforcement leading to de-passivation of the steel and cause corrosion.

Chloride ions can ingress in concrete cover from ambient exposition to the reinforcement steel surface, as the concentration reached critical level the passivation layer of steel will be dissolved.Under presence of moisture and oxygen corrosion reaction will be induced as follows: •

2Fe → 2Fe2+ + 4e- (Anodic dissolving = oxidation)

•

2Fe2 + 4Cl- → 2FeCl2 (Anodic Cl absorption)

•

FeCl2 + 2H2O → Fe(OH)2 + 2Cl- + 2H+ (Cathodic reaction)

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Vol. 48 | Number 4 | December, 2018

Fig. 2: Environment for Concrete to Chloride Threshold Level

4.2 Mathematical Penetration •

Model

for

Chloride

Chloride Penetration

The rate of chloride penetration into concrete as a function of depth is normally modelled by the use of Fick’s Second Law of Diffusion: The Bridge and Structural Engineer

dC(x,t) –––––– = Dc dt

d2C(x,t) –––––– dx 2

(1)

Where, C(x,t) is the chloride ion concentration at a distance x from the concrete surface after being exposed for a period of time t, and DC is the chloride diffusion coefficient. By solving this differential equation for pre-defined boundary conditions, the following equation is obtained: x C(x, t) = Cs 1 - erƒ –––––– 2. √Dt

[

(

)]

(2)

Where, Cs is the chloride ion concentration on the concrete surface, and erf is the error function. Since the diffusion coefficient is time dependant, a commonly used expression.

D (t) = D 0

( ) t ––– to

n (3)

Where, D0 is the diffusion coefficient at the time t0, and the exponent n represents the ability of the concrete to increase the resistance against chloride penetration with time. By substituting Eq. 3 into Eq. 2, an expression is obtained that permits the prediction of chloride levels based on the time dependent diffusion coefficient, given by:

[ (

Cx = Csc 1 - erf •

√(

0.5 x/ Do.

)]

t n –– t to

)

(4)

The probability analysis may be deduced using of a Monte Carlo Method (MCM) simulation. The estimation of the probability of failure is based on the evaluation of the limit state function for a large number of trials. The limit state function g(r,s) <0, where s represents the load and r the resistance, the load s can then be represented as the depth of chloride penetration:

(

)√

t n Do. –– t to

( )

Corrosion

Due

to

The principle of reinforcement corrosion is similar to that of chloride due to Carbonation. Carbonation of concrete occurs due to Carbon Dioxide from the air / atmosphere ingresses through porous concrete, neutralizes the alkalinity of concrete reducing the pH values to 8 or 9 where the oxide film is no longer stable and with presence of moisture and oxygen the reinforcement corrosion may occur. Carbonation ingress though a slow process, the rate is determined by carbon di-oxide penetration in concrete; as explained for chloride ingress, it depends on quality concrete, permeability, porosity and depth of cover for reinforcement. CO2 of the ambient air reacts with Calcium hydroxide on concrete lowering the pH value; where the pH value is less 12 steel will de-passivate and under presence of moisture and oxygen corrosion will start.

4.4 Avoidance of Deterioration

•

Sulphate attack,

•

AAR / ASR (Alkali Aggregate Reactivity / Alkali Silica Reactivity)

•

Delayed Ettringite Formation (DEF)

•

Leaching

•

Shrinkage

•

Stray Current Exposure

•

The above mentioned deterioration parameters needs to be differently resolved by considering Avoidance of Deterioration Approach. The following factors needs to be controlled and are dependent on the quality control at site too

•

Ambient relative humidity

•

Grade of concrete; water cement ratio ; use of SCMs

(5)

Where,cCR is the critical chloride level at which the de-passivation of the steel reinforcement occurs. The resistance r is defined by the depth of the concrete cover. For each trial, the variables are randomly sampled from the probability distribution function that

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4.3 Reinforcement Carbonation

Other Deterioration parameters are as follows

Probability analysis

CCR x(t) = 2.erf -1 1 – ––– CS

represents their scatter, and the limit state function g(r-s)<0 is evaluated. The probability of failure is given by the ratio between the number of trials resulted in a negative performance of the limit state function and the total number of trials. Since the accuracy of MCM mainly depends on the number of trials, and the method is easy to implement, a simulation based on MCM appear to be both simple and intuitive.

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113

•

Placement and compaction of concrete

•

Water-cement ratio

•

Time of exposure

Use of Special Cementitious Material (SCMs) like Pulverised Fly Ash, GGBS, Silica Fumes etc. help in avoiding the deterioration of concrete hence increasing the durability as it decreases porosity and offer good binding strength to concrete. The mix design shall thus include these SCMs inturn increasing the Durability.

Curing of concrete has an important contribution that influences many properties of concrete and impacts directly the strength and service life. Appropriate curing helps in reducing the cracks and improves strength and durability; Increase in curing period increases strength of concrete and decreases depth of carbonation. Curing shall done appropriately by ponding on horizontal surface and using hessian cloth for vertical surface ad ensuring to keep it inundated with moisture all the time during curing period.

Addition of SCMs (Supplementary cementitious materials) such as Fly ash, GGBS etc. in concrete; plastic shrinkage cracking is a possibility and therefore the curing of concrete becomes very important. Initial curing will commence soon after initial setting of concrete or immediately after the stripping of formwork. It is seen that with low temperature curing, a relatively more uniform microstructure of the hydrated cement paste and pore size distribution accounts for the higher strength. Pozzolanic Concrete increases in strength with age if drying is prevented.

Concrete shall not be allowed to dry or moisture shall

not be reduced as it may slow done the strength gain and therefore it is imperative that concrete shall be kept moist as long as possible. It is observed that the strength of the continuously moist-cured concrete is enhanced greatly. It is proposed that curing needs to done with moist covers or ponding initially and later suitable and approved curing compound (membrane curing) will be adopted. Use of SCMs can lead to significant retardation of the setting time, which means that finishing operations may have to be delayed. The rate of the pozzolanic reaction is slower than the rate of cement hydration, and SCMs concrete needs to be properly cured if the full benefits of its incorporation are to be realized. When high levels of SCMs are used it is generally recommended that the concrete is moist cured for a larger periods as compared with OPC in concrete. It has been recommended that the duration of curing be extended further where possible, or that a curing membrane be placed.

5.

Quality Assurance and Inspection / Operational Maintenance

5.1 Testing Regime Durability of the concrete depends on the quality control and the assurance of the delivery of concrete as per the requirement of delivery and therefore it is imperative that the delivered concrete is tested after casting. The permeability, Chloride and Carbonation penetrability shall be ascertained after 28 days of casting. Initially testing frequency may be higher and as the acceptance criteria are consistently achieved it may be lowered. It is though important that the testing criteria is defined to get a fair idea of the durability parameters of the concrete delivered.

Table 1: Minimum requirements for Testing of Concrete a)

For Precast Elements

Sr. No.

Tests

References

Age of concrete

Frequency

Acceptable limits

1

RCPT @ trial mix

ASTM-C 1202

28 days

3 nos.

Average 700 coulombs & ≤1000 coulombs

2

RCPT @ preliminary tests

ASTM-C-1202

28 days

5 nos. 1 in 20 rings

≤1000 coulombs (conforming to ODS)

3

Tests as mentioned in Row-2 for both internal & external faces and the critical face shall be determined and the same face shall be chosen for further sampling. After preliminary tests are acceptable for all 5 sets frequency as mention in row 4 shall be carried out; if not acceptable test mentioned in row-2 shall be repeated.

4

RCPT production segments

114

ASTM-C-1202

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28 days

1 in 120 rings

≤1000 coulombs (conforming to ODS)

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Sr. No.

Tests

5

Permeability @ trial mix

6 7

b)

Age of concrete

Frequency

Acceptable limits

DIN-1048-5

28 days

3Nos.

≤ 10 mm

Permeability @ preliminary test

DIN-1048-5

28 days

5 nos. 1 in 20 rings.

≤ 10 mm

Permeability production segments

DIN-1048-5

28 days

1 in 120 rings

≤ 10 mm

For Cast in Situ Concrete

Sr. No.

Tests

1

• RCPT • Penetrability • Coefficient of permeability (K)

2

References

• RCPT • Penetrability • Coefficient of permeability (K)

References concrete

Age of

Frequency

Acceptable limits

1 Each for 500 m3 for first 03 castings • ASTM-C 1202 • DIN-1048-5 • IS-3085 or Deduced from DIN-1048-5

5.2 Operation and Maintenance Maintenance is conducted to reduce likelihood of failure and to extend the service life of concrete. An optimized maintenance approach focuses on various preventative maintenance schemes. The maintenance strategies of should strike a balance between preventative maintenance and on-demand maintenance. To be effective, the inspections must be structured over the intended service life and both inspections and maintenance. Tunnel investigations are typically carried out to gather information on condition of the concrete delivered and to ascertain the extent of the maintenance required. The aim of inspection is to determine the following aspects.

•

To investigate the extent, severity, cause and consequence of apparent changes in condition (e.g. in response to noted defects or deterioration).

•

To obtain information necessary for the assessment of maintenance, repair or refurbishment needs, and for the design of any associated works.

•

To obtain information necessary for the assessment and design of alterations to the tunnel in response to changes in requirements or in its use.

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28 days 1 Each for every 1000 m3 after tests in point -1 are acceptable

•

• Avg 700 & ≤1000 colmb • 10 mm • 5 x 10-13 m/sec

To establish the structural condition of the before any proposed external development that may influence it.

The optimum inspection interval is likely to differ, depending on their type, condition, deterioration and accessibility, and the consequences of hazards occurring. It is advisable to have regular inspection regime to ensure that any unlikely occurrence of deterioration is attend to at the earliest. Inspections of the types described will require access provisions to be made and for safety precautions to be adopted during the course of the work. Following method is proposed for inspection.

•

Operational Inspection: shall be conducted to suit operational needs for the readiness of the system, any obvious defect and servicing / cleaning to reported and logged.

•

Regular / routine inspection: to be conducted at regular intervals which may include visual inspection to observe and monitor any water leakages, seepages, cracks and deterioration.

•

General inspection: may be conducted at a larger interval than the regular interval and include NDT on the concrete observations for cracks, initial spalling & bulging and to ascertain reasons for

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115

such defects. Inspection may include retrieving a core to ascertain deterioration 6.

Sustainability

In general Sustainability implies that it does not have any net negative impact on the environment.

Production of cement and concrete does have a huge impact on the environment i.e. production of 1000 kgs of Cement around 1000 kgs of CO2 gases are emitted.

Production of cement and concrete is the main source of carbon emissions. Moreover, requirement of clay for the production of cement and requirement of sand and stone as natural aggregates for concrete leads to huge emissions of greenhouse gases and has destroyed natural environment. Use of a large quantity of fresh water for concrete is a heavy burden in addition concrete turns into a large non degradable solid waste after the structure is de-commissioned.

Concrete industry is the largest consumer of natural virgin materials like sand, stones gravel and fresh water. Cement production consumes vast amounts of limestone and clay and is very energy-intensive. It is very important that stress on the sustainability of concrete is given a due attention.

6.1 Supplementary Cementitious Material (SCMs) Use of industrial waste like a) Pulverised Fly Ash (PFA), b) Ground Granulated Blast Furnace Slag (GGBS) c) Silica Fumes (SF) etc. (SCMs or Pozzolans) as partial replacement of cement in in concrete helps in reducing the Carbon footprint of Concrete and helps enhancing properties like strength and durability of concrete. In projects where large quantity is required, High Volume Pozzolans are used to enhance the properties of concrete and reducing the use of cement. The objective of using SCMs other than achieving Sustainability is to obtain a High performance concrete (HPC). HPC not only delivers stronger concrete but durable too and thus making it a Sustainable material.

It is generally observed that a partial substitution of Cement with SCMs in concrete mixture reduces the requirement for obtaining a given consistency.

Depending on the quality and quality of SCMs substantial reduction in water is achieved, this means that SCMs act as a super-plasticizing admixture in concrete. This is due to the particle size and gets absorbed on the oppositely charged surfaces of cement

116

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particles preventing flocculation. The cement particles are thus effectively dispersed and will trap large amounts of water, leading to reduction in water requirement to achieve given consistency helping is delivering high strength concrete.

6.2 Aggregates Use of natural Aggregates in Concrete puts a large amount of strain on the environment due to two main reasons •

Dredging of river to obtain natural sand as fine aggregates: at many places authorities are putting a ban on the dredging leading to a crisis as the demand for natural sand is high in construction industry. As an alternative crushed stone is looked as fine aggregate which is the trend and is delivering acceptable results.

•

Coarse aggregates from stones like Lime stone, Granite, and Basalt is also detrimental to the environment as this requires large scale excavation moreover the stone dust is also used as fine aggregates as a replacement for sand increase the demand.

With increasing concern over the excessive exploitation of natural aggregates, synthetic aggregate produced from environmental waste is a viable new source of structural aggregate material.

Re-utilize solid wastes, such as crushed mixed colour glass, fly ash and rubber particles from waste tires, extensive experimental studies are performed for developing different types of new concretes, glassCrete, ash-Crete, rubber modified concrete, and sulphur rubber concrete. The experimental results show that each of the concretes has some unique properties, with potentials to be utilized in various applications. New trends and advancements in concrete are •

Cement Kiln Dust (CKD)

•

Glass-Crete: Portland Cement Concrete with Waste Glass as Aggregates

•

Ash-Crete: Activated Fly Ash with Glass Aggregates

•

Rubber Modified Concrete (RMC)

•

Sulphur Rubber Concrete Sulphur rubber concrete (SRC)

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•

Geo-polymer and Magnesium Phosphate Cement (MPC)

7.

Conclusions

•

Present Available codes provide deemed to satisfy approach for service life of 100 years and less. Whereas the present infrastructure projects demands service life of 120 years and more.

9.

References

1.

Model Code for Service Life Design- CEB-FIP - fib-34 Proceedings of the International Workshop on Sustainable Development and Concrete Technology – The Consultants View on Service Life Design- Carola Edvarsen Proceedings of the International Workshop on Sustainable Development and Concrete Technology : Beijing, China, May 20-21,2004 Probabilistic assessment of the durability performance of concrete structures by Miguel Ferreira, Said Jalaliof University of Minho, Guimarães, Portugal and Odd E. Gjørv of Norwegian University of Technology and Science, Trondheim, Norway CIRIA-671: Tunnels: Inspection, Assessment and maintenance.

Federal Highway Administration Publication no. FHWA-HIF-15-005: Tunnel Operations, Maintenance, Inspection, and Evaluation (TOMIE) Manual.

Technical Paper : “A trial infrastructure asset management for subway tunnels” by TakaakiNishimurai), Shinji Konishiii, Tetsuya Murakamiiii, Shogo Suzukiiv and HirokazuAkagiv presented inThe 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering Published by Japanese Geotechnical Society Durability Assessment Report: Singapore LTA:Architectural and Engineering Consultancy Services for Eastern Region Line (ERL).

2.

•

To satisfy the project requirement and to deliver desired service life, adoption of the probabilistic approach is more prudent.

•

Probabilistic approach is appropriate, reliable and veracious as it takes into account the probabilistic nature of environmental aggressiveness, degradation process and arrives at optimum material requirement.

3.

4.

5.

6.

•

Durable concrete by defaults delivers sustainability.

•

Adoption of Probabilistic Approach are viable and great benefit to the project Authority / owner, Construction Engineering Professional and Society as a whole.

8.

Acknowledgements

Authors would like to express special thanks of gratitude to Dr. B.C Roy who gave us the opportunity to write a paper on Concrete durability as well as Mr. PughazendhiGaneshan who encouraged and guided us to do study on the subject.

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7.

8.

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117

WATERPROOFING - UNDERGROUND TRANSPORTATION STRUCTURES

Rama Raju PENMATSA

Harshavardhan DESHPANDE

Technical Director AECOM India Professional Engineer, Virginia And West Virginia States, USA MSCE, Structural Engineering, West Virginia University, USA M.Tech. ramaraju.penmatsa@aecom.com

Associate Director AECOM India harshavardhan.deshpande@aecom.com

Experience in Large infrastructure & Water Resources projects in USA & India. Authored and presented several technical papers in Transportation Research Board and ASCE, USA.

Abstract Almost all underground structures suffer from water leakage problems. Approach traditionally to attend to the leakage after it is observed and treated by using injection for waterproofing. This can only reduce large scale water ingress and less effective is preventing water seepage. This leads to corrosion in Steel and aggravating the water ingress and in the long term leading major repairs. It is therefore important that waterproofing is addressed at the design stage. However, data and useful literature on water proofing for the underground structures is available through the waterproofing vendors and manufacturers. This material is obviously biased towards the manufacturer and requires the designer to expend an extraordinary amount of time comparing one manufacture's products against another. The evaluation of a waterproofing product's suitability for performance, application, and general conditions requires the designer to be familiar with a wide variety of engineering disciplines such as chemistry, material sciences, rheology, hydrology, structures and must also 118

Vol. 48 | Number 4 | December, 2018

Experienced Civil / Structural Engineer with Specialization in and all types' transportation structures, Concrete Technology, precast concrete and tall buildings.

possess a considerable degree of construction field experience. Designer with all these qualities would be hard to find and as a consequence designers normally stick to a waterproofing system that they have used in the past with any success rather than conduct the research required to match the proper waterproofing system to the specific project design requirements. This paper presents a study on the study of water proofing system most suitable for underground transportation structures.

Keywords: Waterproofing, Underground Structures 1. Introduction The way in which water flows becomes a very important as the underground structures need to prevent water ingress. For the over ground structures too study becomes important, but until now compliance to the standards and specifications was considered sufficient. But increasing construction of underground Structures waterproofing has taken increasing importance. All underground structures are required to hold water The Bridge and Structural Engineer

tightness as one of the main fundamental characteristics. The underground structure is usually surrounded by underground water / moisture, keeping the water out of the structure is critical to prevent functionality hassles and to enhance the durability. Complicated and advance technology of waterproofing technology is employed, the problem of leakages still exists. The underground structures face the problem of water ingress in the design life of the structure and the dealing with the dewatering of the water is a big problem as it hampers the operations augmented with the durability issues related with water ingress.

Waterproofing system is required to resists liquid state hydrostatic pressure exerted as water finds its path through voids, cracks, joints and capillary action. Water proofing / damp proofing system is required to resists the flow of water / moisture (water vapour) in gaseous state in to the structure.

Leading causes of leakage in underground structures is selection of inappropriate and improper selection of suitable water proofing systems, inadequate detailing by designers, poor workmanship, defective materials, inadequate supervision, and poor construction procedures.

Installers also play a major role in waterproofing system failures as even the best designed waterproofing systems and products will fail if improperly installed due to faulty equipment, untrained workers, insufficient surface preparation, unsuitable application environments, improper cure periods, and unauthorized shortcuts to save money.

This technical study presents the technical evaluation of different types of water proofing systems available for the underground transportation structures.

2. Criteria for Selection of Water proofing To adopt the most suitable water proofing system it is imperative that a study of the soil, ground water condition, topography and rainfall is done and understood to ensure that the structure is protected from water ingress. It is advisable that the structure is protected from the positive side i.e. the waterproofing from a barrier between the water and the structure. It is very important to have required data for the water proofing system to be adopted i.e. coating or membrane type. Though the

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requirement may be of zero water ingress, but many a times even after adopting the most suitable system, water ingress is observed in the service life of the structure. Permissible water ingress i.e. quantity of water / time / area shall be established based on the permeability of soil, ground water flow, etc. These criteria will help in adopting the most suitable water proofing system.

In addition to the above a adoption of good water proofing system is dependent on a) Site, b) structure c) ground and ground water conditions d) specifications e) record of the system f) experience of the installer in delivering required workmanship g) inspection h) Guarantees / Warrantees by manufacturer and installer i) Expected Service Life Based the parameters the selection of the water proofing system shall depend on a) type and depth of the structure b) construction method (Bored, Cut and cover or top down diaphragm wall construction) c) operational maintenance and d) cost of the water proofing system.

2.1 Ground Water Level It is important to determine the fluctuations in ground water level i.e. is the ground water level is constant or fluctuating and its level with respect to the underground structure. Chemical properties of water like, soluble sulphates, chlorides, acids, pH values etc. flow rate of ground water in all seasons, permeability of the soil will also need to be determined.

2.2 Soil Types Soil types such as impervious soils (clays and silts), pervious soils (sand and gravel) and disintegrated and/or solid rocks with water permeability properties. Water retention and dewatering methods; short and long term settlements; and excavation and Construction Methods depend on type of soils as their properties significantly vary.

Chemical Soil contamination tests shall also be investigated all with soil properties.

2.3 Seismic Movement Seismic activity will impact the type of

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119

waterproofing to be used.

Additional considerations are to be taken in to account for Hydrodynamic pressure and structural cracks caused due to seismic forces.

3.

Types of Waterproofing

Waterproofing is a relatively impervious membrane, coating, or sealer used in concealed locations to prevent water from entering or passing through either horizontal or vertical building materials. Waterproofing is designed to exclude water even when the water is under a hydrostatic head. Waterproofing is different than the damp proofing or water repellents, which are used to reduce water penetration. Waterproofing is a coating or a sealant to prevent water from entering.

Waterproofing is designed to exclude water from the contact of structural elements.

Different types of water proofing systems are available in the market. There are different types waterproofing and can be broadly classified as follows: z z z z z z

Liquid systems or mopped system Swelling Barrier type system Sheet membranes Epoxy systems Sprayed systems Hybrid systems

Based on Methods of application the water proofing system can broadly classified as z z

Pre-applied Post applied

Based on Material used for the water proofing, the classification is as follows z z z

Bituminous Cementitious Membranes

British Standard 8102:2009 defines the water proofing system as follows. z z z

120

Type A : Waterproofing Barrier Materials Applied to the Structure Type B : Structurally Integral Watertight Construction Type C: Cavity Drained Construction.

Vol. 48 | Number 4 | December, 2018

3.1 Liquid Type Waterproofing Liquid waterproofing makes the structural surface resistant to water ingress by applying coating on the surface. These coating may be single component or multiple component. Liquid water proofing systems are very easy to apply on surfaces hard to reach and irregular surfaces with complex geometry.

Liquid waterproofing membrane is available in the form of liquid and is sprayed or applied by brush or roller to the concrete surface which forms a thick joint free membrane in contact with air. The benefits of this process lies in its simplicity to apply and by default delivers a joint free system. Larger area can be covered in a short period of time and requires less skilled labours for application. The elongation of this system needs to be carefully study before adopting as poor elongation leads to separation from the substrate, movements in the substrate makes the system prone to splitting and tearing.

3.2 Swelling Barrier type system This system uses Bentonite encased in fabric or board. The characteristics of this system is that it swells forming a barrier between the water and structure, when in contact with water. It easy to apply on flat surfaces. Treatment of the points is a difficulty making the joint leak prone, and requires a protection over the system.

The most likely material used for this type of water proofing is Bentonite. Installation requires time and care to make it full proof as nailing is the way it is attached to the concrete surface of the underground structures and needs a second layer of sealing. The Bentonite prone to segregation leaving undetected

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voids that allow leakage. The system requires completely dry surface as well as weather.

3.3 Membrane type water proofing Membrane type water proofing system is used in Under Ground Metro for the NATM tunnel and cut and cover Stations. The systems predominantly of two types fully bonded and un-bonded.

Un-bonded membranes are sheet membrane systems with different materials and mostly used in NATM tunnels, they are loosely laid sheet membranes, since there is no bond between the membrane and structural face, water migrates through membrane joint and/or from membrane damaged areas. Now the migrated water fills the empty space between the membrane and face of the structure. In the unbonded membrane water is prone for migration, and if ingress of water happens, it becomes extremely difficult to determine source of leak making the repair and maintenance expensive. Un-bonded waterproofing system is susceptible to compromise and rarely produces a satisfactory, long-term solution and in an underground structure the repairs are very expensive and unreliable and mostly unsuccessful.

Water ingress into the structure may cause damage to the structure and the attached facilities. To avoid costly repairs and downtime, a more reliable waterproofing system is required. When it comes to waterproofing membranes and technologies, the performance of a bonded membrane systems far surpasses than un-bonded systems. Relying on an

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un-bonded waterproofing system can leave a building vulnerable to defects and damage hampering the functionality of the structure. A bonded waterproofing system addresses the shortfalls of un-bonded membrane systems. The key is the bonding technology, which forms an impenetrable seal with structural concrete. It ensures that it remains in position and prevents water ingress or migration, even in harsh climates and challenging site conditions. Fully bond membrane prevents lateral migration of water between membrane and concrete face. Fully bonded membranes are either liquid applied or sheet applied membranes glued to the concrete surfaces.

Fully bonded waterproofing membrane sheet adheres to the concrete due to the heat generated and the pressure while concreting. The fully bonded membrane thus forms a part of the concrete structure and behaves like one entity.

Membranes like Polyolefin co-polymers, Flexible Polyolefin (FPO), Styrene Butadiene- Styrene (SBS), Ethylene Propylene Diene Monomer (EPDM) and High Density Polyethylene (HDPE) are available. HDPE Membranes are more durable, resilient and flexible than any other bonded and/or un-bonded systems. Other membrane systems are less durable and are susceptible to damage. Because of the better properties Fully Bonded HDPE membrane is suitable for the water proofing of underground structures. HDPE sheets edges if not sealed properly are prone to Hydrocarbon attack and therefore installation shall be carried out by skilled installers. It is being used in many metro underground structures in Europe, Middle East, Singapore and Malaysia. In a recent project in Doha, Qatar, fully bonded Water proofing HDPE membrane was applied to a temporary shoring wall, and wall was cast against it. Three years after, the temporary wall was removed.

During excavation, the contractors found that the exposed HDPE waterproofing membrane was fully bonded and performed to the expectations.

3.4 Epoxy Liner System Epoxy liner systems have two different formulations for vertical and horizontal surface

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applications.

The formulation adheres to the surface without any sag / vertical downward flow. The installation is by spraying the epoxy over the surface. It is very easy to apply though requires specialised protection equipment. The application is seam less and delivers a very good adhesion to the RCC surface if the surface thoroughly cleaned and dry. The product application needs specialized skilled labours as the material is very flammable and explosive. After application requires inspection to ensure application is appropriately carried out to cover the surface.

3.5

and polymer additives. Cementitious coatings are predominantly used from the negative side (interior) for repairs and rehabilitation works. This is a good product as a backup system for areas where exterior waterproofing has failed. This system is a rigid system and will crack and leak if the structure moves.

3.6

3.6.1 Poly Rubber Gel Utilizes the mix of rubber and polymers. A flexible membrane is applied by pressurised spraying system. The system has good elongation and flexibility, the application is fast, can be applied immediately after stripping of form work. Recycled material can be used making the material green material. The system requires a protection board after application, requires a dry surface. The material is very thick product which requires a special pump to apply. It is cold applied and therefore does not need a kettle.

Other Sprayed Systems

3.5.1 Sprayed cold applied neoprene Sprayed cold applied neoprene is a single component material which can be applied on concrete immediately after the de-shuttering.

It has an excellent elongation and forms a good protection against water ingress due to crack formation. It is easy to apply and does not necessarily require dry surface. This system requires healing time, requires clean surface for adhesion and if not cleaned properly may form blisters as concrete cures, requires protection board after application against damage.

3.6.2 Waterproof Concrete Concrete Prepared with concrete additives to reduce the pore size and to prevent the passage of water molecule particularly Calcium Sterite. The inherent property of concrete to shrink as it cures thus the term waterproofing concrete is misleading.

Concrete cannot be made waterproof without a membrane. The use of waterproofing concrete reduce the permeability of concrete is effective and is used in combination with the water proofing systems to decrease the permeability of the concrete and is extensively used in Asia for underground MRT projects. The system is good in Arid Climate and is water resistant but not waterproof.

3.5.2 Poly-urea Spray Coating System Poly-urea as waterproofing material is similar to the material used for automobiles.

It is a rigid and is heat applied to concrete surface and has excellent bonding property.

This material delivers hard finish, cures rapidly. As the material is rigid the elongation properties are limited. The surface needs thoroughly cleaning and requires heating while application. Poly-urea Coating is fairly new and has limited track history as water proofing material.

3.5.3 Cementitious Waterproofing Systems Cementitious waterproofing systems are a mixture of OPC, pozzolans like PFA, GGBS 122

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Hybrid Systems

3.7

Water proofing System Conforming to BS8102-2009

3.7.1 Type A Waterproofing Barrier Materials Applied to the Structure A physical barrier will be created to stop water entering into the structure. They are The Bridge and Structural Engineer

often used for the projects, such as Underground Metro Stations, Medical and N u c l e a r Facilities, Luxury Apartments or any other finished a) Type A (barrier) protection spaces that would Key r e q u i r e 1 External waterproofing 2 Masonry or concrete wall, as prevention from appropriate (see Table 1) water, moisture, 3 Concrete flood slab waterproofing or vapour 45 Sandwiched Loading cost infiltration into 6 Internal waterproofing the structure. The water barrier method is also the most suitable method where water level is constant and above the roof level (Close to the water bodies).

Type C -Cavity Drained Construction is also adopted along with membrane system as stand by system for continuous function of intended use of the structure without any interruption. It is acceptable to use drainage protection for critical structural elements. The risk of failure will be significantly reduced by using combined waterproofing barrier protection system with cavity drainage system.

3.7.2 Type B: Structurally Integral Watertight Construction Using waterproofing admixtures in concrete as a waterproofing method for underground transportation structures is being practiced.

Concrete with waterproofing admixtures in s t r u c t u r a l elements is often less expensive option compared to Membrane Barrier and

b) Type b (structally integral) protection Key 1 2 3 4 5 6 7

Water-resistant reinforced concrete wall and slab External or internal (within wall) waterstop, as required Waterstop required at junction between wall and slab and at all construction joints Concrete/steel piled wall Water-resistant reintofced concrete floor slab or slab with added barrier Waterstop at junction to follow profile of wall Piled wall might need to be fixed to achieve desired water resistance (see Table I)

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Cavity Drained waterproofing systems. It is easier and simpler method as there's no separate application involved.

Waterproofing admixtures are simply incorporated into the concrete mix. There is also little to no maintenance involved if concrete mix design and concrete placement is done properly. Concrete with waterproof admixture is a good option for low- to medium-risk projects such as a concrete parking garage where small amount of moisture is acceptable.However, no concrete is 100% resistant to water infiltration so waterproof concrete alone is not the best choice for high risk projects or finished space. For Table 1 mentioned in the figure Refer BS-8102-2009.

3.7.3 Type C: Cavity Drained Construction Cavity Drained Construction system as waterproofing method works well for situations when c) Type c (drained) protection the use of an e x t e r n a l Key 1 Cavity drain membrane w a t e r p r o o f i n g 2 Inner skin (render, dry lining or walling, on system) membrane is not 3 depending Maintainable drainage channel with pipe conection to suitable discharge point practical and/or it 4 Sump formed in situ or pre-formed is not possible to 5 Pump Wall cavity achieve continuity 67 Reinforced concrete/steel pile or diaphragm wall of an external 8 Drainage channel w a t e r p r o o f i n g 9 Waterstop at junction to follow wall profile m e m b r a n e . 10 Internal block wall Drainage systems 11 Access point(s) to drainage slab with integral protection and/ do tend to be 12 Flood or added membrane (internal or external) expensive, however, especially when you consider the cost of upkeep and maintenance. The systems need to be monitored to make sure they don't get clogged. In addition, backup generators are needed in case of a failure. In general, drainage systems are not usually recommended for projects where there is a high water table, a fluctuating water table, or where there is contaminated soil, because allowing the water and/or vapours from contaminated soil into the structure is Vol. 48 | Number 4 | December, 2018

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obviously not ideal. Cavity Drained Construction system as waterproofing method works well for situations when the use of an external waterproofing membrane is not practical and/or it is not possible to achieve continuity of an external waterproofing membrane. Drainage systems do tend to be expensive, however, especially while considering cost of upkeep and maintenance. The systems need to be monitored to make sure they don't get clogged. In addition, backup generators are needed in case of a failure. In general, drainage systems are not usually recommended for projects where there is a high water table, a fluctuating water table, or where there is contaminated soil, because allowing the water and/or vapours from contaminated soil into the structure is obviously not ideal.

4.

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Swelling Rubber Water-stops Another way of treating the cold joint is to use swelling type water-stops. The swelling waterstops is a polymerised rubber that swells when in contact with water. The installation of the swelling rubber water stop must be at a minimum offive (5) cm in from the face of the concrete walls. This is necessary to prevent the swelling action of the rubber from spalling the concrete.

4.3

Injection Water-stops Water-stops that allow the injection of grout to seal the leaking joint is inject Waterstop.

This requires a tube to be placed at the junction of concrete at intervals which facilitates injection of grout at a later time when seepage is observed.

Though the system has little success as they are required to be placed with extreme caution to prevent concrete infilling and are often available for one use only. Due to this issue the system shall be used as a backup system and not as a primary system.

Vinyl or PVC Water-stops Water-stops is placement across the joint to prevent the flow of water through the joint. The traditional water-stop for concrete cold joints is the traditional dumbbell (due to shape)Waterstop made of vinyl, PVC or rubber. These water-stops are partially placed in the first

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4.2

Water proofing of Construction and cold joints

Cold joints and penetrations are the most common cause of leakage in an underground structure.

Appropriate detailing of joints therefore becomes very important. With the adoption of best available water proofing system, if the Joints treatment is not appropriate then it may lead to breech of water proofing and require special treatment to prevent water from entering the structure. In general the materialsused for sealing joints a referred to as water-stops.

4.1

pour and held in position in the second pour thus creating difficult path for the water preventing the water to flow through the joint. The installation of water-stop is labour intensive and requires care to prevent damage while installation.

In fact the combination of all the above three shall be adopted for the treatment of joints against water ingress.

5.

Conclusions

Depending on the profile soil substrate, availability The Bridge and Structural Engineer

of the space and the structure type, the most suitable of the water proofing systems discussed in this paper may be adopted. The adopted system shall be important to the successful specification and installation of waterproofing systems on underground concrete structures. These elements are interdependent. The structural concrete design, product selection, installation details, and quality of workmanship are of equal importance to the functioning of installed system. However, system selection involves decisions based on Judgement of the engineer. It is therefore prudent that before a waterproofing system is selected manufactures, material experts, designers, and installers act as a team in the selection of an appropriate waterproofing system. The bottom line to the selection of a waterproofing system is to provide a system that is leak free. Performance of the installed waterproofing depends on identification of all related factors and parameter correctly. It is observed that leakages in underground structures are prevalent and these trends will be reduced only after the design team does a thorough study and specifies the appropriate system after discussion with the manufacturers and installers.

Present trend is to provide Fully Bonded Sheet and Liquid Membrane Systems which avoid the need of compartmentalization; and repair methods are easy simple, and cost effective.

HDPE Pre and Post applied membranes have better performance history and will have long service life as the material is inert. Membranes have good physical properties and good UV and chemical resistance. HDPE membranes are most suitable for Base Slabs and for the walls two component Poly-urea and Polyurethane liquid membranes also

The Bridge and Structural Engineer

good performance history. Membranes have good physical properties and good chemical resistance.

Liquid membranes are most suitable for Roof Slabs and Walls.

Industry practice is to use Swell bars and ReInjectable hose system at both vertical and horizontal construction joints and proved to be very efficient system repair and maintenance system.

6.

Acknowledgments

The Authors would like to express deepest appreciation to all those who provided the possibility to complete this study. We give a special gratitude to Mr. Pughazendhi Ganeshan and Dr. B.C. Roy, their vast experience in the field of underground transit structures helped us to understand the subject and present this study.

7.

References

1.

Waterproofing of underground Structures by Tim Biggins University of Florida 1990.

Guidelines for Waterproofing of Underground Structures by Parsons Brinckerhoff December 2008.

Singapore LTA Specifications Code of practice for protection of below ground structures against water from the ground - BS 8102:2009 Best Practice Guidance - Type A,B,C Waterproofing Systems; Property Care Association The Manual of Below - Grade Waterproofing; Justin Henshell, 2nd Edition, Routledge, London and New York.

2.

3.

4.

5.

6.

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COST OPTIMIZATION FOR UNDERGROUND METRO PROJECTS: IN INDIA Rajendra HARSH B.E., MBA Chief Cost Control Specialist rajendraharsh@icloud.com

Summary Since 1972 when foundation stone of first Metro rail Project of 17 kms completely underground except terminal stations in Kolkatta to the year 2017 when Metro Rail Policy was announced, metro rail industry in India has come a long way. This project of Kolkatta Metro which started with the budget of around Rs150 cr in 1972 got completed in the year 1992 with the cost of around Rs 1475 cr. Since then Time and Cost overruns are common for Metro rail Projects till date.

In this paper we are just trying to raise some issues and suggest probable solutions for cost optimization in Initiating and Planning stages of the project. The purpose is only to start a discussion, draw attention of experts and initiate brainstorming.

Keywords: Cost Optimization, underground, metro rail projects, time and Cost Overruns 1.

Introduction

Metro rail Project Cost increases from At-Grade to Elevated to Underground projects. In this paper we are concentrating only underground metro rail projects although major issues are common for all types of metro rail projects. The main cost factors that an Underground Metro Rail Project encompasses are Civil Costs, Rolling Stock costs, Signalling and Telecom Costs, Taxes & Duties, however cost and time over runs are mainly because of Land, R&R and Environmental issues.

In any project, cost control plays an important role.

Normally in Metro Project, Cost Control procedures

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Vol. 48 | Number 4 | December, 2018

Rajendra Harsh, born 1955, received his electrical engineering degree and MBA from the University of Jodhpur, India. He has 35 years of experience in various infra projects which includes more than seven years as Finance and Cost Expert in Metro Rail Projects

are primarily intended to estimate revised cost at the time of evaluation of Bids; to arrive at revised estimated completion cost for reporting to stake holders; estimate cost for deviations and to make payments to contractors rather than to plan strategies in initial stages of project in Initiating and Planning, for Execution, Monitoring & Controlling and Closing stages of the project for optimization of the cost.

There are risks associated with all the stages of the project. These can be classified into Political, Social, Environmental, Financial, Technical, Resources etc.

Risks can further be classified as high, medium and low probability risks. Risks have mitigation cost.

Political and Social Risks if not mitigated in the initial stage of the project before awarding any contract, will have castigating effect by way of claims from all the contractors and therefore should be identified and mitigation plan for the same should be detailed in Project Charter itself. Costs of Land, R&R and Environment management may be only around 3% of the project but if these issues are not addressed timely, it will directly increases the cost substantially of at least Civil Contracts which may cross 50% of total costs.

In this paper we will try to adopt model based on our experience in implementing projects in India and also the model suggested by Project Management Institute (PMI) in their PMBOK. This paper will focus on projects being executed by Central & State Government joint ventures partially financed by international funding agencies. We will not be focusing on Metro Rail Projects in Public Private Partnership

The Bridge and Structural Engineer

(PPP) Model, although most of the strategies will also apply to PPP Model.

There are five Process Groups during the project cycle namely Initiating, Planning, Executing, Monitoring & Controlling and Closing. It is said that â&#x20AC;&#x153;well begun is half doneâ&#x20AC;? and thus in this paper we will be discussing first two processes Initiating and Planning.

2.

Initiating

Various cost components and their contribution to overall costs ranges may be assumed as mentioned below for the purpose of discussions in this paper: Above percentages are for a typical project where majority land parcels are given free of costs by the government, completely underground, with a very high traffic expectations, funded by international agencies

with an interest rate of around 1% per annum and to be completed within five years once majority of civil contracts are awarded.

All the elements of cost are to be properly thought, researched (historical review of similar, comparable projects in India and abroad), planned and strategically addressed during this process.

This process includes developing Project Charter, Identifying Stake holders and deciding Organisations to own, execute, monitor, control and setting up standards. Normally when any project is started, Business Documents, Agreements, Organisational Process Assets and Enterprise Environmental Factors are used as Inputs for Preparing Project Charter and Assumption Log. However, additional inputs are also required to be looked into and therefore, an effort is being made to

Table: Cost Componentsof a 100% underground metro rail project with very high PHPDT Sr No

Cost Head

% Range of Total Cost

A

CIVIL COSTS

1

Tunnels and Stations (Around 97% of Civil Costs) Including Utilities Shifting, Street Decking,Traffic management etc.

2

Depot (Around 3% of Civil Costs)

B

SYSTEMS COSTS

1

Track Works (Around 10% of System Costs)

2

Tunnel Ventilation and Environment Control Systems at Stations (13% of System Costs)

3

Power Supply and Traction (Around 11% of System Costs)

4

Signaling, Train control,Telecommunication and PSD (Around 15% of System Costs)

5

Rolling Stocks (Around 40% of System Costs)

6

Plant & Equipment for Depot (Around 1% of System Costs)

7

Automatic Fare Collection (Around 3% of System Costs)

8

Lifts and Escalators (Around 6% of System Costs)

9

Station Security System (Around 1% of System Costs)

C

LAND , R&R AND ENVIRONMENT MANAGEMENT COSTS

2.5-3.5%

D

PROJECT MANAGEMENT AND PRE-OPERATIVE COSTS

3.5-4.5%

E

FINANCE COST

2.5-3.5%

F

ESCALATION DURING CONSTRUCTION

G

CONTINGENCIES

2.5-3.5%

H

TAXES AND DUTIES

12-13%

Total Completed Project Cost

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45-55%

13-17%

8-10%

90%-110%

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127

highlight some of the important issues. Every suggestion mentioned here may be referred to experts to work out an appropriate approach.

document these discussions, permissions required , issues for the purpose of further negotiations or for submission to courts by Owners. A detailed Plan including Legal advice, acceptable R&R plan and alternative solutions may be examined along with Detailed Project Report (DPR).

1.1 Project Charter ¾

Creating Cost, Schedule and Scope Baselines:

While preparing Detailed Project Report (DPR) from Conceptualisation, traffic and ROW surveys, concept designs, technologies, scope, time schedule, cost estimates, identifying stakeholders, their requirements and influence; following to be discussed with various experts and a historic review of earlier similar and comparable projects should be done thoroughly; to arrive at realistic baselines, assumptions and approach towards project which will finally lead to cost optimization. ¾

In cases where Metro Rail Projects are envisaged in a city which is under new development, a transport model can be planned ab-initio with the alternative of having Metro Rail At-Grade instead of combination of elevated and underground. Alternative of At- Grade right of way (ROW) with combination of having under passes and foot over bridges may also be convenient for public in addition to affordable cost.

¾

In some cities like Ahmedabad there is a ROW already acquired by railway which passes through the heart of the city which is either unused or underutilised. Possibility of building Metro Rail Project At-Grade at the already identified ROW may be examined into for reducing overall Cost Optimization. Underground Metro projects are the most expensive compared to At-Grade and Elevated Metro Projects and therefore study of all other alternatives is advised. It may require legislative, administrative decisions in using ROW already occupied by Railway or other government agencies and the same to be explored keeping in mind that taxpayer is the same in all cases.

¾

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Agency engaged to identify Stakeholders having Old buildings, Heritage Sites, Buildings and Land parcels required to be acquired should have detailed discussions with stakeholders (relevant public persons/ bodies, relevant government agencies, active NGO,s and legal experts), Vol. 48 | Number 4 | December, 2018

¾

Agency for Geological Survey should do detailed survey with sufficient numbers of Bore Holes so that at the time of construction repetition of the same is not required to save cost and time.

It may be a good idea to engage the same agency for any further Geological Surveys if required during execution of the project to optimize on cost & time and for the benefit of continuity and exclusive responsibility.

¾

Agency engaged for surveying trees to be cut or transplanted should have discussions with relevant government departments& NGOS active in the City and try to get consent on cutting, planting and transplanting of trees. A detailed plan identifying Land Parcels for Tree Plantation, numbers and types of Trees to be planted, identification of trees to be transplanted etc with the in-principal permission/acceptance of such plan by relevant statutory bodies should be acquired and submitted along with DPR. It is suggested to cover a detailed note of the types of trees to be planted from the view point of local availability, type of soil, local weather conditions and the trees which can absorb pollution.

¾

In many of DPR it has been noted that timelines are assumed as if the project will commence on the day they submit DPR. However in many cases it has been found that first Civil Contract is being awarded in the year in which project was planned to be commissioned. Realistic timelines should be adopted so that one can have near to realistic estimated costs, FIRR and EIRR. As discussed earlier it is suggested that commencement of project should be arrived by taking into consideration of time span to settle all R&R, Land acquisition, agreements/ permissions of government agencies / trusts/ owners of Old buildings and Heritage sites/ NGO’s issues before awarding the major civil contracts.

The Bridge and Structural Engineer

¾

It is suggested to include a chapter on Lessons Learnt by various Metro Rail Projects in India detailing the reasons for cost overrun and time overrun by other projects and the mitigation plans adopted by them. This study becomes very useful in preparing Risk Mitigation Plan for the project under consideration.

¾

Agreements Agencies:

¾

It may be a good idea to engage Consultants/ Agencies who are preparing DPR during the whole life cycle of the project till project is handed over to operating agency to optimize on cost & time and for the benefit of continuity and exclusive responsibility. It should also be responsible for studying reasons of variation in cost, time schedule and technical parameters and submit revised reports at pre-determined intervals with revised estimates of Project Completion Cost, FIRR (Financial Internal Rate of Return) and EIRR (Economic Internal Rate of Return) at different stages of project to the stake holders. Such arrangement coupled with answerability might improve the quality of the DPR and will be instrumental in reducing variations and cost overruns.

with

Consultants

and

1.1.1 Organisation Structure ¾

Present Organizational Structure for owning and executing Metro rail projects are MOUD Delhi, MOUD of State, JV of Central and State Governments with part funding from Multilateral Agencies like JICA ADB etc. For Project management initially Interim Consultant (IC) and then General Consultant (GC) are being appointed with top layer of Expats, who through International Bidding appoints Contractors to execute the projects. Duplication of these consultants with Detailed Design Consultants Lead Design Checkers are not only increasing direct costs but more than that indirect cost by increasing time for execution.

¾

As on date, various metro rail projects, although owned by governments are being executed by different Joint Venture Companies like DMRC, KMRCL, BMRL, CMRL, MMRCL, MMRDA, Maha Metro, Kochi Metro, MEGA, Jaipur Metro etc.

The Bridge and Structural Engineer

¾

Instead of having multiple organisations, it is high time to consider one organisation like Railway with some modifications in Standard Operating Procedure for executing the projects with International Bidding process which is necessary to get projects funded by multilateral funding agencies. For crucial areas if there is need to hire experts (Indian or Expat) with international experience on roll with relaxation in age on contractual basis to improve the efficiency by this new single organisation. Present process appoints Consultants for DPR, followed by DDC, LDC and IC then GC who basically works as manpower provider at exorbitant cost. It is suggested to have a top layer of experts in long term employment which can be efficiently utilised for all the metro projects in country with support of second layer of experts. This top layer of international experts (Not necessarily Expats) should be paid as per international standards. It will not be out of place to mention that first metro project in India around fifty years back was designed and executed by mostly Indian Experts.

1.1.2 Organizational Process Assests (OPA) & Enterprise Environmental Factors (EEFs) ¾

Present OPAs and EEFs are similar in nature for all Metro Rail Projects as all Metro JVs are PSUs. But, each project is a different entity and therefore Lessons Learnt in different organisations remain private and it takes same time for every new organisation to set up procedures, policies and mature a professional culture on its own. If we have “One” organisation on the lines of Indian Railway or like Metro Rail, Kolkata within India Railway we need not spend time, efforts and resources in setting up anew organisation. Its Policies, Standard Operating Procedures, IT systems, Corporate Office need not wait for developing a professional culture every time a new project is implemented resulting in Cost Optimization.

With the number of Metro Rail Projects now already completed it will be possible to create Organizational Knowledge Base by standardising technical specifications, designs, schedules, Bidding Documents, approved vendor lists and materials and creation of Schedule Rates for Civil as well as all the systems, resulting in cost optimization.

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¾

¾

¾

A legal Frame work is urgently needed for all Metro rail Projects to avoid delays in acquiring land parcels, rehabilitations, permissions for tree cuttings and to settle issues related to religious places& heritage structures so that these issues can be settled in a time bound manner to avoid major Cost Over Runs. It has been seen that time taken in setting up a new JV and settling these issues after preparation of DPR is more than the total duration of Project execution. Projects in the year when they should have commenced Revenue Operations struggles with these External Environmental Issues in the absence of such an effective legal frame work.

It is suggested to bring legislation by central/ state governments to limit NGOs who can approach judiciary for stalling infrastructure projects by way of legalising eligibility criteria.

Such eligible NGOs and public residing in influence zone of ROW (500 meters either side) should be given sufficient chance to raise their objections within specified time period and the hearing of all such issues by a statutory authority should be completed within a stipulated time period.

A new Legislation for compensation package for the public residing in zone of influence during the project implementation like rebate on property tax, water, electrical and sewerage charges and building up new civic facilities like stadium/play grounds etc. may be very helpful to bring these stakeholders on board.

of delaying the project. Reduced risk will thus help in Cost Optimization.

2.

While integrating all subsidiary plans of scope, schedule, cost, quality, resources, communications, risks, procurement and stakeholders into overall Project Management Plan by using Project Charter and Stakeholders Register following may be considered to optimize the costs: 2.1 Scope management plan While collecting requirements, defining scope, creating of WBS it should be kept in mind that numbers of packages have direct relation to costs. Too many packages will increase overhead costs while too few packages will increase the bidders’ overhead costs.

To secure sufficient competition without sacrificing over dependence on one or two contractor, optimum numbers of packages is essential for cost optimization.

2.2 Schedule management plan To optimize costs by reducing risks for contractors claims during construction, competitive rates from bidders and thus reducing probabilities of cost and time over run following activities preferred to be completed before starting any major civil construction: ¾

Complete the process of acquiring clear possession of 100% land required for the project.

¾

Receive all approvals from Archaeological/ Heritage Department or other relevant government agencies by submitting detailed plans of safeguarding heritage and old structures in influence zone.

¾

Complete formalities of rehabilitation of affected citizens, acquiring accommodation for them and moving them satisfactorily on temporary or permanent basis as required.

¾

Widely publicising positive effects of completed project, difficulties to be faced by public and effect on environment during implementation (e.g. noise pollution, traffic congestion), acquiring public land parcels (e.g. parks, play grounds etc. on temporary basis for construction), objections to be received by public, hearing by an authorised statutory body and measures being taken by project implementing agencies to bring on board

1.2 Identify Stakeholders ¾

130

A detailed study of all stake holders is of utmost importance. Identifications, Contact details, influence zones, requirements, reasoning, worries of all Stake Holders including general public, NGOs, governmental agencies should be studied in detail and recorded in Stakeholders Register.

Focus groups including groups on social media should be created to create a positive environment for the project and address the different requirements of various Stakeholders.

A detailed study at this stage of initiating project is necessary to prepare effective Plan for Stakeholder management and reduce the risks

Vol. 48 | Number 4 | December, 2018

Planning

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all residents in zone of influence and eligible NGOs. ¾

A compensatory package for the public residing in zone of influence during the project implementation may be announced like rebate on property tax, water, electricity and sewage charges and building new civic facilities etc. to bring them on board.

in a specified time period. This Dispute Resolution Board should meet once a month and conduct discussions with employer and contractor to settle conflicts before these result in time and cost over runs. ¾

In international bidding allowing of foreign currencies are normal and desired by multilateral funding agencies. If foreign currencies are limited to actual spend in that currency it is a win-win situation for employer, therefore, while preparing contracts terms it should be specific for providing payment in foreign currency only against the proof of spending in the foreign currency to the satisfaction of employer. Looking to fact that INR is devaluating fast Vis-a-Vis USD it is an important component to optimize the costs. Bidding in foreign currencies should not become a source of income/loss for contractors as both the situations are not in the interest of cost optimization.

¾

Most bids in Metro Rail Projects are Design and Built and therefore payments are not made against Bills of Quantities (BOQ) but on the basis of achievements of milestones. It makes difficult to estimate costs accurately based on Last accepted Rates (LAR) of similar contract and therefore an averaging method of cost estimates may be applied for comparison with DPR rates after adjusted these costs for the lapse of years which is normally 5-7 years. For escalation change in WPI during the period can be a good indicator.

¾

For managing costs during the execution of project Price Adjustment Formulas are very important. A general formula as suggested by one of international funder is as mentioned below:

2.3 Cost management plan Cost management plan establishes how the cost will be planned, structured and controlled. To optimize the costs for metro rail projects, estimated costs before floating bids, strategies to convey the estimates in bids, preparing optimum qualifications criteria (technical as well as financial), ensuring enough competition among qualified bidders, deciding payment terms, deciding conditions regarding payments in foreign currencies are important factors. Detailed brain storming sessions among cost, finance, contract and technical experts are required to decide measures for cost optimization.

Some of the suggestions are mentioned below: ¾

Deciding technical and commercial parameters for Pre-qualifications of bidders should be optimum for not getting bidders who can’t deliver, at the same time to have enough bidders to have good competition.

¾

To have lenient payments terms for easy cash flow for contractors so that they load minimum finance cost but at the same timerobust escrow system should be put in place to ascertain that funds released for the project are not diverted for other purposes.

¾

¾

¾

To optimize operational costs, including Comprehensive Maintenance Contracts in bids for contracts, for 5/10 years can be considered.

Bidders normally bid around the estimates on which bids have been prepared. This can be easily arrived by back calculation of parameters like financial and bidding capacity. While deciding these parameters project manager may decide parameters which are based on optimum costs which may be lesser than budgeted costs.

Contract terms should have a provision for ongoing Dispute Resolution Board with a mandate that every dispute small or big is settled

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[ ( ) ( ) ( ) ( ) ( )]

L1 S1 C1 SC1 F1 P1=Po a+b –– +c –– +d –– +e –– +f –– – Po Lo So Co SCo Fo

Where: P1 is the adjustment amount payable to the contractor Po is Contract Price (Base price) of Interim Payment Certificate under consideration a is a fixed coefficient as specified, representing the nonadjustable portion in contractual payments; b, c, d, e and f are coefficients representing the estimated proportion of each cost element ( e.g. Labour, Steel, Vol. 48 | Number 4 | December, 2018

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Wires & Cables, Semi-Conductors and Fuel respectively) in the Facilities or sections thereof.

L1, S1, C1, SC1 and F1 the applicable cost indices ( e.g. Labour, Steel, Wires & Cables, SemiConductors and Fuel respectively) on the date of adjustment, determined from the Named / Published Source of Index, applicable to each cost element; and Lo, So, Co, SCo and Fo are the base cost indices (e.g. Labour, Steel, Wires & Cables, Semi-Conductors and Fuel respectively) or reference prices corresponding to the above cost elements at the Base date, determined from the Named / Published Source of Index.

In some of the bids it has been seen that coefficients a,b,c,d,e,f have been left to bidders to select the values for these coefficients. It is suggested that these coefficients should be decided while floating bids so that it remains same for all bidders. Selection of indices and coefficients values should be done after brainstorming among technical, cost and contract experts.

interest rates of INR it may be a good idea of considering funding by Perpetual Bonds from Indian Public.

2.6 Communications management plan Plan to ensure timely and appropriate collection, creation, distribution, storage, retrieval, management; monitoring and ultimate disposing the information is the key to timely execution of the project.

2.7 Risk Management Plan When Owner passes the Risk to Contractor, contractor not only adds mitigation cost but also overhead and profit on the same. If the Risk considered by a contractor while entering into the contract does not materialises its mitigation cost with overheads considered turns into increased profit of the contractor. ¾

Some of the risk mitigation costs may be covered by insurance and thus has definite mitigation costs. Some of the risks’ mitigation costs cannot be estimated e.g. political and social etc.

Furthermore Political and Social Risks if not mitigated in the initial stage of the project before awarding any contract will have castigating effect by way of claims from all the contractors.

¾

For cost optimization of a Metro Project it is suggested that all risks related to Land, R&R, and Environment which can be best handled only

by Central and State Government, risks having low probability of materialising and the risks of which mitigation costs cannot be estimated should not be transferred to contractors. Risks which have high probability and/or for which mitigation costs can be determined by way of insurance should only be transferred to the contractors to optimize the costs.

¾

Risks related to safety, traffic handling, environment and health may become crucial and a detailed plan should be prepared for that. If these humanitarian issues are not nipped in the bud they might get escalated and turn into major factors for time and cost over runs. The Safety Health and Environment (SHE) Chiefs’ appointment along with Project Manager by contractor should be made compulsory in initial stage of implementation and may be made pre

2.4 Quality management plan A detailed, workable with optimum quality standards and unambiguous Quality Management planis necessary to avoid disputes and thus time and cost overruns. While preparing bids a detailed guideline should be mentioned for bidder to submit their Quality Management Plan to monitor their performance against the same.

2.5 Resource management plan Project financed by governments and international agencies have long lead time and therefore timely update of the project, funds received, used and required for balance time period of the project should be kept ready and submitted to funding agencies well in time so that contractors can be paid well in time.

An additional standby limit from banks may also be kept sanctioned and available for exigencies. To monitor the availability of resources by contractors contract terms should be added into bids for use of Project Management Software like ERP/ PRIMAVERA/UNIFIER etc. for managing their resources efficiently and ensuring that there are no delays on account of non-availability of resource.

Funds from international funding agencies run the risk of foreign exchange rates. Looking to the falling 132

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condition of making payment of mobilisation advance.

¾

Before awarding a contract to any bidder one must consider the financial capabilities of that party. Failure in doing the same can lead to a catastrophe. If the party is unable to fulfil its duties, it will lead to major time overruns, which will lead to cost overruns and it might also raise disputes which can again add to the cost of the project and delay the project at the same time.

In international bidding it is always advisable to use Standard Bidding Documents of various international institutions like FIDIC or funding agencies like JICA, ADB, World Bank etc. for pre-qualification and inviting bids.

3.

Conclusion

2.8 Procurement management plan The process of documenting project procurement decisions, specifying the approach to identify, prequalify bidders, preparing bids and selecting the appropriate contractor at the most optimum cost is one of the various factor of cost optimization. We need to consider following while preparing Procurement Plan: ¾

¾

¾

Presently in the country most of the contracts are awarded on Design Built basis. With decades of experience in Metro Rail Projects enough knowledge base is available in the country for changing this process to BOQ bids for all the contracts except may be for Rolling Stock and Signalling, Train Control and Telecom. Detailed designs can be done in house or a separate contract can be awarded. BOQ contracts reduce the risks for contractors compared to Design Built contracts and thus will help in reducing costs.

Presently in the country most of the contracts call for prices inclusive of all taxes. These taxes are collected by Central, State Governments and being allotted back to Metro Rail Projects as means of finance by way of interest free subordinate debts. Contractors need to incur cost not only for tax amount but also overheads and finance costs. Furthermore in case of change of legislations these taxes also become the cause for disputes. To avoid all such costs it may be better to exempt all the state and centre taxes for metro rail projects owned and executed by Centre and State government joint ventures.

Present government has a great emphasis on Make in India but ironically fifty years back Rolling Stocks for First metro rail Project were designed and manufactured in India except small portion of technical knowhow. Since then mostly all Rolling Stock are being imported. This issue coupled with selection gauge may be brain stormed once again to reduce the costs, including maintenance costs on spare parts and saving of foreign exchange.

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Major suggestions to optimize costs of underground metro rail projects owned and executed by Centre State government joint ventures in India are as mentioned below: ¾

Setting up a new central organisation on the lines of Indian Railway under Ministry of Railway or under separate ministry for all metro rail projects.

¾

Setting up a separate body for technical knowledge on the lines of RDSO.

¾

This new organisation should be flexible in creating a top layer of experts of international standards.

¾

Creating Schedule of Rates for various Civil and Systems specific to different types of mono and metro rail projects.

¾

Creating Standard Operating Procedures and Standard Bidding Documents to be used in planning and execution of all projects.

¾

Extensive study is required related to Land, R&R, Environment, Old/Heritage structures and identification of all stakeholders with their requirements, objections and plans to mitigate their concerns during and post the implementation of the project while preparing DPR.

¾

New legislations to smoothen the process of addressing concerns of all stakeholders.

Eligibility criteria to be set for NGOs who can raise issues through PIL. Only residents residing

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in zone of influence and qualified NGOs are allowed to raise environment issues. ¾

Changing bidding process from Design Built to BOQ for the most of contracts.

¾

Awarding construction contracts only after all the issues related to Land, R&R, Environment, Old/Heritage structures are settled.

¾

Recording of lessons learnt and data base of designs and costs incurred. This data base is to be made available for all the metro rail projects.

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4.

Acknowledgement

I would like to acknowledge the time and effort spend

by Dr B. C. Roy in reviewing this paper. He is well known expert in structural engineering. He has worked as Team Leader and Project Director in various phases of First Metro Project of India which also crosses River Hugali. He has been involved in many other Metro projects and was leading Nairobi transit Master plan. He was also Project Incharge in many large infrastructure projects including Commonwealth Games at Delhi.

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INDIAN NATIONAL GROUP OF THE IABSE OFFICE BEARERS AND MANAGING COMMITTEE â&#x20AC;&#x201C; 2018 Chairman 1

Shri BN Singh, Director General (Road Development) & Special Secretary to the Government of India, Ministry of Road Transport and Highways Vice-Chairmen

2 3 4

Shri RK Pandey, Member (Projects), National Highways Authority of India Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt Ltd Shri SP Singla, Managing Director, SP Singla Constructions Pvt Ltd Past Chairman

5

Shri DO Tawade, Member (Technical), National Highways Authority of India Honorary Treasurer

6

The Director General (Road Development) & Special Secretary to the Government of India, Ministry of Road Transport and Highways Honorary Members

7

Shri Ninan Koshi, Honorary Member, IABSE & Former Director General (Road Development) & Addl. Secretary

8

Prof SS Chakraborty, Honorary Member & Past Vice-President, IABSE

9

Dr BC Roy, Honorary Fellow & Past VicePresident, IABSE

Persons represented ING on the Executive Committee and Technical Committee of the IABSE

Honorary Secretary 13 Shri IK Pandey, Additional Director General (Road Development), Ministry of Road Transport & Highways Members of the Executive Committee 14 Shri AD Narain, Director General (Road Development) & Additional Secretary 15 Shri AK Banerjee, Former Member (Technical), NHAI 16 Shri G Sharan, Former Director General (Road Development) & Special Secretary 17 Shri AV Sinha, Former Director General (Road Development) & Special Secretary 18 Shri RP Indoria, Former Director General (Road Development) & Special Secretary 19 Shri Ashwinikumar B Thakur, Group Engineer, Atkins India 20 Shri RK Jaigopal, Consultant, Concrete Structural Forensic Consultant 21 Prof Mahesh Tandon, Managing Director, Tandon Consultants Pvt Ltd Past Secretary of the Society, for a period of two years, after they vacate their Secretaryship 22 Shri RK Pandey, Member (Projects), National Highways Authority of India Secretariat

10 Dr Harshavardhan Subbarao, Vice President & Member, Technical Committee of IABSE & Chairman and Managing Director, Construma Consultancy Pvt Ltd

23 Shri IK Pandey, Additional Director General (Road Development), Ministry of Road Transport & Highways

Past Member of the Executive Committee and Technical Committee of IABSE

24 Shri Ashish Asati, General Manager, National Highways Authority of India

11 Prof SS Chakraborty, Honorary Member & Past Vice-President, IABSE

25 Shri KB Sharma, Under Secretary, Indian National Group of the IABSE

12 Dr BC Roy, Honorary Fellow & Past Vice President, IABSE

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MEMBERS OF THE MANAGING COMMITTEE – 2018 Rule-9 (a): A representative of the Union Ministry of Road Transport and Highways

19 Shri Akhilesh Upadhyay, Chief Engineer (Bridges), Govt of Madhya Pradesh

1

20 Shri Ajit Arvind Sagane, Secretary (Works), Govt of Maharashtra

Shri BN Singh, Director General (Road Development) & Special Secretary to the Government of India, Ministry of Road Transport and Highways

Rule-9 (b): A representative each of the Union Ministries/Central Government Departments making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time

21 Govt of Manipur – nomination awaited 22 Govt of Meghalaya – nomination awaited 23 Shri Bowman, Chief Engineer (Planning), Govt of Mizoram 24 Govt of Nagaland – nomination awaited 25 Govt of Orissa – nomination awaited

2

CPWD - nomination awaited

3

Shri DO Tawade, Member (Technical), National Highways Authority of India

27 Govt of Sikkim – nomination awaited

4

Ministry of Railways - nomination awaited

28 Shri A. Venkatachalam, Divisional Engineer Tamil Nadu Sector Project-II

Rule-9 (c): A representative each of the State Public Works Departments/Union Territories making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 5

Govt of Andhra Pradesh – nomination awaited

6

Shri Kenjom Ete, Chief Engineer (Eastern Zone), Govt of Arunachal Pradesh

7

Govt of Assam – nomination awaited

8

Govt of Bihar – nomination awaited

9

Govt of Chattisgarh – nomination awaited

10 Shri Umesh Mishra, Principal Chief Engineer, Govt of Delhi 11 Shri U.P. Parsekar, Principal Chief Engineer, Govt of Goa 12 Govt of Gujarat – nomination awaited 13 Govt of Haryana – nomination awaited 14 Govt of Himachal Pradesh – nomination awaited 15 Govt of Jammu & Kashmir – nomination awaited 16 Govt of Jharkhand – nomination awaited 17 Govt of Karnataka – nomination awaited 18 Govt of Kerala – nomination awaited

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26 Govt of Punjab – nomination awaited

29 Shri P Satish, Chief Engineer (R&B), Govt of Telangana 30 Govt of Tripura – nomination awaited 31 Shri Yogendra Kumar Gupta, Chief Engineer (Bridge), Govt of Uttar Pradesh 32 Govt of Uttarakhand – nomination awaited 33 Govt of West Bengal – nomination awaited 34 Shri Mukesh Anand, Chief Engineer-cum-Special Secretary (Engg), Union Territory Chandigarh Rule-9 (d): A representative each of the Collective Members making annual contribution towards the funds of the Indian National Group of IABSE as determined by the Executive Committee from time to time 35 Major VC Verma, Director (Mktg), Oriental Structural Engineers Pvt 36 Shri SP Singla, Managing Director, SP Singla Constructions Co Ltd Rule-9 (e): Ten representatives of Individual and Collective Members 37 Shri G Sharan, Former DG (RD) & Special Secretary 38 Shri AK Banerjee, Former Member (Technical), NHAI

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39 Shri AV Sinha, Former DG (RD) & Special Secretary

55 Shri Bageshwar Prasad, CEO (Delhi Region), Construma Consultancy Pvt Ltd

40 Shri RP Indoria, Former DG (RD) & Special Secretary

56 Shri RV Chakrapani, Chief Consultant, Aarvee Associates Architects Engineers & Consultants Pvt Ltd

41 Shri Ashwinikumar B Thakur, Group Engineer, Atkins India 42 Prof Mahesh Tandon, Managing Director, Tandon Consultants Pvt Ltd 43 Shri RS Mahalaha, Advisor, ITL

Rule-9 (i): Honorary Treasurer of the Indian National Group of IABSE 57 The Director General (Road Development) & Special Secretary to the Govt of India

44 Shri RK Jaigopal, Consultant, Concrete Structural Forensic Concrete

Rule-9 (j): Past-Chairman of the Society, for a period of three years, after they vacate their Chairmanship

45 Shri Rakesh Kapoor, Oriental Consultants India

58 Shri DO Tawade

46 Shri Inderjit Singh Ghai, CEO, Consulting Engineers Associates

Rule-9 (k): Secretary of the Indian National Group of IABSE

Rule-9 (f): Four representatives of Bridge and Structural Engineering Firms

59 Shri IK Pandey

47 Shri VN Heggade, Sr Vice President & Member Board of Management, Gammon India Ltd 48 Shri Asutosh Mathur, Vice President, GR Infraprojects Ltd 49 Shri T Srinivasan, Vice President & Head â&#x20AC;&#x201C;Ports, Tunnels & Special Bridges, Larsen & Toubro Ltd 50 Shri Dhananjay Achyut Bhide, Consultant, IRB Infrastructure Developers Ltd Rule-9 (g): Two representatives of the Engineering Colleges / Technical Institutes / Universities /Research Institutes

Rule-9 (l): Persons who have been awarded Honorary Membership of the Parent Body 60 Shri Ninan Koshi 61 Prof SS Chakraborty 62 Dr BC Roy Rule-9 (m): Persons represented ING on the Executive Committee and Technical Committee of the IABSE 63 Dr Harshavardhan Subbarao

51 The Director, SERC, Chennai

Rule-9 (n): Past Members of the Executive Committee and Technical Committee of the IABSE

52 The Director, Indian Railway, Pune

64 Prof SS Chakraborty

Rule-9 (h): Four representatives of Consulting Engineering Firms

65 Dr BC Roy

53 Shri AD Narain, President, ICT Pvt Ltd 54 Shri Alok Bhowmick, Managing Director, B&S Engineering Consultants Pvt Ltd

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Rule-9 (o): Past Secretary of the Society, for a period of three years, after they vacate their Secretaryship 66 Shri RK Pandey

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HIGHLIGHTS OF THE ING-IABSE WORKSHOP ON “INSPECTION, INVESTIGATION AND REPAIR/REHABILITATION OF BRIDGES & FLYOVERS” HELD AT CHENNAI ON 8TH AND 9TH DECEMBER, 2018 The Indian National Group of the International Association for Bridge and Structural Engineering (ING-IABSE) in association with Ministry of Road Transport & Highways and National Highways Authority of India organised a two day Workshop on “Inspection, Investigation and Repair/ Rehabilitation of Bridges & Flyovers” on 8 th and 9th December 2018 at Chennai. The aim of the two-day Workshop was to provide insights into the probable causes of distress of bridges and techniques available for their repair and rehabilitation to enhance their service life. It also covered the aspects of detailed inspection, investigation and testing.

The Workshop was inaugurated on Saturday, the 8th December 2018 by lighting of the traditional lamp by Shri I.K.Pandey, Secretary, ING-IABSE and Additional Director General (Road Development), Ministry of Road Transport and Highways and other dignitaries on the dais, which included Shri Ninan Koshi, Chairman, Scientific Committee & Honorary Life Member, IABSE, Shri AK Banerjee, Co-Chairman, Scientific Committee, Shri Alok Bhowmick, Vice-Chairman ING-IABSE and Dr. Harshvardhan Subbarao, Vice President IABSE. Shri Alok Kumar Pandey, Regional Officer, Chennai, Ministry of Road Transport and Highways extended a warm welcome to the gathering and Shri Pawan Kumar, Regional Officer, National Highways Authority of India proposed a Vote of Thanks.

A view of the Dais during the Inaugural Function

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The Workshop was well attended by more than 300 delegates from various organizations. The active participation of the delegates contributed to the overall success of the Workshop.

The programme of the Workshop was brought to a close on 9th December, 2018 with the concluding remarks of Shri I.K. Pandey, Secretary, INGIABSE and Additional Director General (Road Development), Ministry of Road Transport and Highways.

The detailed programme of presentations during the two-day workshop made by various eminent experts in the field, was as follows:

Saturday, 8th December 2018 Session-1 “Inspection, Investigation and Bridge Management System” Session Chair

Keynote Address Shri I.K.Pandey, Secretary, ING-IABSE and Additional Director General (Road Development) Ministry of Road Transport and Highways lighting the traditional Inaugural Lamp along Presentation-1 with high dignitaries

– Shri N.K. Sinha, Former DG (RD) & Spl Secy, MoRT&H – Shri Ninan Koshi, Chairman, Scientific Committee Bridge Repair & Rehabilitation – An Overview – Shri A.K. Banerjee

Presentation-2

Client’s Perspective –

Shri I.K. Pandey

Presentation-3

Condition Survey and Bridge Management System – Dr. Lakshmy Parameswaran

Presentation-4

Detailed Investigation and Testing – Shri R.K. Jaigopal

Presentation-5

Development of BMS for National Highways – A Case Study – Shri R.S. Sharma

Session-2

“Repair Materials and Techniques”

Session Chair Presentation-6 Presentation-7 Presentation-8 Session-3 Session Chair

- Shri R.P. Indoria, Former DG(RD) & Spl Secy, MoRT&H FRP A Wonder Material for Repairs – Prof. M.C. Tandon Some New Technologies, Concepts and Case Studies in Bridge Repairs – Dr. Harshavardhan Subbarao Concrete Bridge Repair – State of the Art and Materials & Methods – Shri Samir Surlaker

“Repair / Rehabilitation and Case Studies” - Shri Amitabha Ghoshal, Chief Advisor, STUP Consultants

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Presentation-9 Presentation-10 Presentation-11

Rehabilitation of Bridges & Other Structures – Shri P.Y. Manjure Repair and Retrofitting of Bow String Arch Bridges in Goa – Shri Alok Bhowmick The Use of the base isolation for the reduction of Earthquake actions on the Structures – Shri Enzo Lu

Sunday, 9th December 2018 Session-3

“Repair / Rehabilitation and Case Studies” (Contd…)

Session Chair

- Shri A.D. Narain, Former DG(RD) & Addl. Secy, MoRT&H

Presentation-12

Rehabilitation of Steel Bridges – A Case Study – Shri Amitabha Ghoshal

Presentation-13

Hybrid Technology for Rehabilitation of Deep Bridge Foundations – Shri V.N. Heggade

Presentation-14

Rehabilitation of Durgabati Bridge on N.H 2 in Varanasi – Shri Umesh Rajeshirke

Presentation-15

Repairs to major cracks in Main Span of Versova Bridge across Vasai Creek – Shri Aditya Sharma

Presentation-16

Specialized Replacement Techniques of Bearings and Expansion Joints with Minimal Disruption of Traffic – Case Studies – Shri Prateek Sen

Shri Alok Kumar Pandey, Regional Officer, Chennai, Ministry of Road Transport and Highways Delivering his welcome address

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Shri Pawan Kumar, Regional Officer, Chennai, National Highways Authority of India Proposing a Vote of Thanks

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Session-3

“Repair / Rehabilitation and Case Studies” (Contd…)

Session Chair

- Shri Ninan Koshi, Former DG(RD) & Addl Secy, MoRT&H

Presentation-17

Rehabilitation of Suspended Span of Versova Bridge across Vasai Creek – Shri Dhananjay Bhide

Presentation-18

Repair and Rehabilitation of Steel Bridges – Shri Ashok Basa The keynote address of the Workshop delivered by Shri Ninan Koshi, Chairman, Scientific Committee on 9th December 2018 was as under: Repair and rehabilitation of bridges is a subdiscipline of bridge engineering that has grown in importance by leaps and bounds in the last few decades. This is because all bridges as they grow older are subject to deterioration due to age and several other factors. It may be recalled that till the eighties there were hardly any companies specializing in bridge repairs other than the Freyssinet Prestressed Concrete Company (FPCC) of Mumbai. We would turn to them every time any problem connected with repairs arose. But since then, as the volume of work in this field has grown rapidly and the complexities involved in repairs have increased, more firms are now available to take up such work, which is as it should be.

Bridge infrastructure in the country consists mainly of reinforced concrete, prestressed concrete and steel structures. Over the service life of a bridge, its constituent materials are continually subjected to Shri Ninan Koshi, Chairman, fatigue and wear and tear due to dynamic loads from Scientific Committee moving vehicles. Gross overloading of trucks causes Delivering his Keynote address the bridge to be subjected to loads far in excess of during Inauguration the design loads. The problem of overloading is one which we have not been able to tackle effectively even now. Prestressed concrete bridges very often exhibit loss of prestress over time, resulting in drop in load carrying capacities of affected members.

Poor quality of construction and lack of regular maintenance also lead to major problems requiring repairs. Expansion joints and bearings may also require rehabilitation or replacement over time.

Concrete is a versatile, economical and successful construction material. Worldwide it is used more than any other material in construction of infrastructure. It is normally strong enough to perform well throughout its service life. However, in many cases it does not do so due to poor design, poor construction, wrong selection of materials or a more severe environment than anticipated. An RCC girder bridge built in 1942, which is still in use although of narrow width, that it appeared to be in perfect condition. It was quite amazing to see the quality of construction achieved by the engineers of those times, even though modern methods of mixing, placing and compaction of concrete were not available to them. It only shows that those early engineers had great respect for concrete as a material and concrete bridges.

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A view of the audience during the Inauguration

Regular and systematic inspection of bridges is an activity that is most often neglected by the engineers in charge of our highways. PWD were maintaining a bridge requirement where they are needed inspection note every six month. In this regard, the Railways have a well established system that is worth emulating. They have designated bridge inspectors who are tasked with regular inspection of their bridges and recording of their observations. These help to monitor the health of the structures and are invaluable in deciding the timing and nature of repairs or rehabilitation that may become necessary at any later stage.

In this context, it may be appropriate to make a mention the stone arch bridges built by the British in the latter half of the 19th century and the first half of the 20th. These bridges were built mainly in Madhya Pradesh and other surrounding regions of central India where good rock foundations are available. Many of them are still intact even though more than a hundred years old. The arches were normally semi-circular in shape but elliptical arches with larger spans have also been adopted. They were constructed by stone masons who were exceptional masters of their craft. Sadly, these skilled artisans have disappeared from the scene and stone masonry arches are no longer being built in India. The stone masonry arch in addition to its aesthetically pleasing appearance also has the advantage of being practically maintenance free. It has no components which deteriorate with passage of time. In fact, tests have shown that the strength of the arch increases as it grows older. As these arch bridges were constructed well before the advent of motor vehicles in India, they were quite narrow in width. Therefore, when widening of the road had to be undertaken, regrettably most of them had to be demolished and replaced with comparatively less aesthetic concrete structures.

The earlier perception was that a concrete bridge once constructed, would look after itself and needed little maintenance. Engineers seldom went under the bridge to see what was happening to the underside of the girders and slabs. It has to be clearly realised that all bridges undergo deterioration with age and require continuous maintenance. We are now designing bridges for a service life of 100 years. Apart from routine maintenance, the bridge, as it grows older, will require at least two or three major interventions during that period to mitigate the effects of ageing and bring it back very nearly to its original level of service. In addition, special repairs will become necessary if and when

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the bridge suffers damage due to accidents, earthquakes, landslides and floods. Therefore, it is essential that the routine as well as long term maintenance of bridges is given adequate attention.

(Unfortunately, there is a lack of appreciation of this requirement not only among engineers but more so among bureaucrats who control the release of funds for government public works departments). As the stock of bridges grows larger, the maintenance budget requires to be as big if not bigger than that for new construction. It is worth noting that in Europe, the outlay on maintenance of bridges is higher than that on new construction.

Delivering his Keynote Address

In 1950, the length of NHs in the country was about 20,000 km only. Over the next five decades, the growth in length was quite sluggish but since 2000, it has been rapid and the total network length now stands at more than 1,30,000 km. This means that the number of bridges on NHs has also grown rapidly, necessitating huge increase in requirement of funds for their proper upkeep and maintenance. However, as I mentioned earlier, maintenance funds are always squeezed and this is bound to have an adverse effect on the health of the structures in the network. Apart from the expansion of the national highway network, as more all weather connectivity is being provided

Another view of the audience during the Technical Session Inauguration

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across the country, more bridges are coming up on SHs and other lesser category roads also, for which state governments are required to set aside adequate maintenance funds.

A bridge management system (BMS) is essential for managing bridges throughout the period of their operation and maintenance. As funds available for maintenance are always tight, road authorities around the world are facing challenges related to bridge management and the escalating maintenance requirements of the growing number of bridges. Bridge management systems help highway departments to meet their objective of planning their maintenance, repair and rehabilitation interventions in a systematic way and prioritizing the allocation of funds.

Once the condition survey of the bridge has been completed and the need for repair / rehabilitation has been established, the next step is to select a suitable agency for carrying out the same. As mentioned earlier, bridge repair and rehabilitation is a very specialised job and hence should be entrusted only to companies having previous experience in effectively carrying out such work with best results in the shortest possible time.

Once the repair / rehabilitation has been completed, it is necessary to provide suitable instrumentation on the structure to monitor its subsequent performance. When the new Mandovi bridge was constructed in the early nineties, it was one of the first instances where instrumentation was provided. However, it appears that over the years, the instruments fell into disuse and readings could not be continuously taken. Also, vandalism resulted in many of the instruments being pulled out and damaged.

The Indian National Group of the International Association for Bridge and Structural Engineering, is one of the most active of the sixty-odd groups worldwide of the parent body in Zurich. As part of its efforts in furthering its objectives, ING-IABSE is conscious of the need for bringing the topic of repair and rehabilitation of bridges into greater focus. Towards this end, ING-IABSE organise number of workshops similar to the present one and are planning to do more in future. Some of the best brains in the field of bridge engineering in the country have been brought together to give presentations based on their vast experience on the various aspects of repair and rehabilitation of bridges. I am sure these will broaden the horizons of the participants on this subject and enable them to take appropriate action when dealing with the requirements of repair and rehabilitation of the bridges on their own highway networks.

A Group photograph of Speakers and Workshop participants

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With Best Compliments From:

ËËËËËËËËË Ë Ë Ë

M/s HK TPL OM Expeses A

152

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

With Best Compliments From:

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M/s M Vediappan

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

153

With Best Compliments From:

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M/s Oriental Structural Engineers Pvt Ltd

154

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

With Best Compliments From:

eee

M/s IRB Infrastructure Developers Ltd The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

155

With Best Compliments From:

M/s L&T Trans Infrastructure

156

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

With Best Compliments From:

eee

M/s Javid Hussain

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

157

With Best Compliments From:

eee M/s Krishnagiri Walajapet

158

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

With Best Compliments From:

vvvv

M/s SPL Infrastructure Pvt Ltd

The Bridge and Structural Engineer

Vol. 48 | Number 4 | December, 2018

159

160

Vol. 48 | Number 4 | December, 2018

The Bridge and Structural Engineer

With Best Compliments From:

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M/s KNR Constructions Ltd

Approved by: MORT&H, DGS&D, RITES & RDSO

‘SAI’ - an ISO : 9001 & CE Certified Company for Design, Manufacture & Supply of all types of Bridge Bearings, Spherical Bearings, Expansion Joints, Hydraulic & Prestressing Jacks, Sheathing Pipe, HDPE Pipe, Anchorages for Prestressing

SAI - Range of Products

STEEL AUTO INDUSTRIES Works & Office: 484, Kishanpura, Damla, Dist. Yamuna Nagar - 135 001, Haryana, India.

If any Queries.. Call or Contact us at: Hotel J.K. Residency, Residency Road, Model Town, Yamuna Nagar -135 001, Haryana, India.

Tel: 224835, 261624 -26, Fax: 01732-229980, Mob: 93550 01414, 97283 14000.

Email: jkgroup1954@gmail.com, steelautoind1954@gmail.com. Web: www.steelautoindustries.com