TunnelTalk Special Edition Focus Ground Freezing

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SPECIAL EDITION FOCUS: GROUND FREEZING

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In-tunnel PSV fire incident report TunnelTalk reporting s was promised, the report into the fire that destroyed a PSV passenger service vehicle on the HS2 Chilterns high speed rail TBM drive in the UK in May 2022 is published and made available to the wider industry by HS2 Ltd, the client, and Align JV, the contractor.

An exact cause of the fire is inconclusive as the burnedout vehicle was too damaged to allow deeper forensic study. The report reveals that the vehicle was running on HVO, hydrotreated vegetable oil, fuel in place of standard diesel and in efforts to run a environmentally friendly, low carbon foot print project. The fire broke out in the engine bay of the vehicle and one scenario is that a frayed fuel line allowed HVO to spill onto hot surfaces and ignite.

Another scenario was that fuel pipes covered with steel wire could have caused arcing if in contact with live electrical terminals.

The Shenzhen-Zhongshan fixed sea link highway across the Pearl River estuary in China is currently under construction and is scheduled to open to traffic in 2024. Connecting Shenzhen in the east with the cities of Zhongshan and Guangzhou Nansha in the west, the 24km long ShenZhong link passes over and under three of the busiest shipping lanes of the world on a suspension bridge with a main span of 1,666m, a cable-stayed bridge with a main span of 580m and transitions on two man-made islands into a 5km long immersed tube structure and a 485m cut-and-cover section extending from the east landfall near Shenzhen. The link is a highway of four lanes in each direction, eight lanes in total, with one special element of six lanes in each direction, and designed for traffic speed of 100km/hr and a design life of 100 years. After about four years in construction, the mega link, which is similar in scope to the recent Hong Kong-Zhuhai-Macao immersed tube and bridge highway link project, is about 50% completed. The authors, as Acciona reporting from a paper members of the ShenZhong Link Administration Center owner organisation, highlight the design and construction of presented at WTC 2020, Malaysia the widest immersed tube tunnel in the world.

The hope ishethat sharing ofcontract the investigation andand Ski. To meet the criteria, Folloa similar Line construction between Oslo findings of established another fire incident tunnelling projectspecified in strict criteriaontoa avoid the contract two main methods for the UK will settlement follow the example.

It was inprotecting September, andsame damage to environment the natural ground water regime any existing and building and toThames avoid water ingress during excavation: at theand start of thestructures TBM drive underalong the River alignment ofhighway the 20kmtunnel long twin tube to • the A watertight for thetheSilvertown project east of precast concrete, bolted TBM bores railway connection andcaught gasketed segmental lining and London that partonofthe thenew conveyor haulage system fire and brought six fire engines and about 40 firefighters to the site at about 10.30pm to manage the incident. The fire was on a section of the conveyor at the portal where muck transitions to a vertical conveyor for onward transfer to surface muck management systems. A photo taken of the night scene by a passer-by has been shared on social media and by UK construction magazines. Finding of the investigation into what caused the fire and the reparation measures taken by Riverlinx, the construction consortium, and TfL, Transport for London, the client, as a result is yet to be published or made publicly available. n

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Systematic and specified pre-excavation Liu Jian, Chen Yue, Jin Wenliang and Song Shenyou, ShenZhong Link Administration Center Dec 2021 grouting as a mandatory requirement at specific locations and in others, a requirement for the contractor to he ShenZhong bridge and tunnel combination across the Artificial islands determine the extent of pre-excavation Pearl River estuary is located at about 40km upstream of the Construction of the west transition island and of the east island grouting required to maintain the ground Hong Kong-Zhuhai-Macao immersed tube and bridge link that water levels. and it 485m cut-and-cover section, completed before sinking of opened to highway traffic in October 2018 and 38km downstream The contract established and defined the immersed tube elements, employed two different methods grouting requirements, and also provided of the Humeng Bridge. The project is built above and beneath the for their diverse conditions. information on grouting concepts, busiest with shipping channels in the world with more than 4,500 vessels the contractor required to further develop The east island, close to the Shenzhen coastline, passes under passing every day. The tunnel at the east end of the 24km long x these concepts and the chosen methods of the Guangzhou-Shenzhen Riverside Highway. To safeguard mostly eight lane highway is required also to maintain the clearance construction to maintain the existing ground it continuing operation, the highway owner required that the of the Shenzhen international airport flight path. water levels. Assessing the potential for limitation water maximum horizontal displacement of less than 5mm for the 38 ingress into the headings was via probe drilling The immersed tube section of the link between the east and by drill rigs installed on the first backup gantry of its support piers that lie within the island. Piers near the tunnel 2 2 close to the shields and drilling 44mwest long man-made islands of about 370,000m and 130,000m are surrounded by 1.4m diameter steel pipes filled with reinforced probe holes. The contract pre-established the respectively, consists of 32 elements of 10.6m high x 46m wide and concrete as retaining structures with other piers protected by number of probe holes that were required in long with a special 55m wide x 123m long 12 lane element 165m steel sheet piles. In this area, the water depth is about 4m and areas previously classified as highly sensitive. and a 2m long closure joint. the thickness of the underlying soft soil is between 8m and 15m.

Pre-grouting was triggered by ingress of Robbins 13.77m diameter Crossover machine ready ground water through the probe holes.

Using traditional artificial island methods, the soft soil under the for excavation of the 3km Eşme-Salihli rail tunnel Initially, Bane Nor, the client, estimated

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Dual-mode TBM begins rail drives in Sicily

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There was little structural damage to the segmental lining of the tunnel with localised damage to a high-voltage electrical cable, the ventilation duct and to the invert concrete slab needing replacement and repair.

A full copy of the published report is available for download and a report about the initial incident was published by TunnelTalk in May.

Silvertown tunnel conveyor belt fire in the working portal job site lights the night sky

May 2022

Toto and CREG tunnelling crews at the launch ceremony in earlyprobe Marchdrilling concept with the litres of water per minute from Above: A two-hole each triggering the need for pre-excavation water control grouting The TBM is named Below: Drilling equipment on the first gantry of the TBM backup allowed for full Margherita after the Toto 360˚ grout injection arrays General Manager’s daughter

TunnelTalk references • Improving TBM fire safety - June 2014

pre-grouting quantities in the TBM headings as about 1,600m in total or some 4.4% of total 36km of bored tunnel length when Norway excavation of the parallel tubes by four double shield TBMs from a central access adit towards the portals began their work in 2016. When both tubes and the last two TBMs completed their drives in February 2019, the total length of pre-excavation grouting executed was in fact 8,000m or some 22.22% of the total bored length. Preexcavation grouting was a major part of the excavation process and required team work with the client to optimise the process, meet the water control criteria and maintain the project programme.

The contract described the drilling equipment to be installed on the TBMs to comply with the probing and pregrouting requirements. Based on this, the following equipment was installed on each machine: • Two Atlas Copco COP3038 drill rigs with 185º rotation capacity • A TC 42 short twisted splins shank adapter • 12ft x 39mm round TC 42 extemsopm rods • A C12ft x 46mm round TC 42 RND 46 speed guiding rod

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he advantages of steel fibre reinforced precast concrete (SFRC) segmental linings have been engaged by some countries now for many years.

Other countries have taken a different route towards researching, testing, developing and approving the steel fibre alternative to traditional steel rebar cage reinforcement for segmental linings. In France the effort has been spearheaded by construction company Eiffage for its €1.84 billion Direct contract by on the Grand Paris Design Express expansion of the Paris Metro.

Jean-Luc Bischoff, Directeur Opérationnel of Eiffage Underground Projects, explains the genesis and journey of the adoption of the technology in France.

Robbins News Release

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• Sprinkler limitations for tunnel fire fighting - September 2011 • Mobile furnace for in-situ fire safety testing - August 2012

13.77m diameter Robbins Crossover XRE TBM is launched recently in Turkey to excavate the 3km EşmeSalihli rail link through mixed conditions, including sandstone, gravelstone, claystone, and siltstone. Contractor Kolin Construction expects some occasional groundwater and weak rock between 5 MPa to 9 MPa UCS, with the potential for a gassy environment.

The TBM is launched after more than seven years in storage, and following a few upgrades to systems to ensure they meet the newest safety and efficiency standards. The hiatus in progress followed cancellation of the original railway project and the wait for a new project and construction contract to be developed for the single-tube, double-track, segmentally-lined section of the new railway.

To get through the challenging conditions, the large diameter Robbins XRE machine has a number of particular features. The large diameter design enables both a screw conveyor and1 a transition belt conveyor to remain in place, enabling swift conversion for operations in 100% closed EPBM and open hard rock excavation modes.

In EPB mode, the screw conveyor

• Managing safety under Sydney Harbour - August 2017 • Evacuating on elevated running tunnel walkways - May 2018 • TTS and BTS supporting safety awareness - April 2020 The references below are hotlinked to articles in the Archive of the TunnelTalk.com web magazine. The web magazine link currently show a security warning as we undertake every effort to regain control of the magazine and restore it to serve the industry and the readers. Although the warning is there, it is the genuine TunnelTalk.com site and we hope to regain access to apply the new SSL certificate just as soon as possible.

Grand Opening

Starting from the premise that hard rock TBMs have poor adaptability to adverse geology, unknown faults, karst caves, groundwater bodies and fractured rock zones, the research team at Shandong University in China has developed an automated geological forward prospecting technique. The authors describe how the system for mounting on TBMs, offers an effective approach for locating and imaging adverse geology for up to 100m ahead of the face to ensure safe and efficient TBM tunneling. etection of adverse geological conditions ahead of hard rock TBM drives is an important prerequisite for the safe and efficient construction of TBM tunnels. Many TBM drives over the years have encountered geological disasters, resulting in TBM blockage or damaged, heavy economic loss and in some cases personnel casualties. Forward prospecting of adverse conditions ahead of the cutterhead is of crucial importance for project success.

To address this requirement, a technique has been developed to detect geological anomalies ahead of an advancing hard rock TBM tunnel face. There are traditional geological prospecting methods used with drill+blast excavation, but these present great challenges when applied to TBM drives: • TBMs provide little space availability for prospecting; • Electromagnetic and vibration interferences are severe and affect the effectiveness of signals; and • TBM tunnelling is five to 10 times faster than traditional drill+blast, requiring faster detection techniques.

To address these problems, the automated geological forward prospecting technique is developed to be mounted on TBMs and is based on seismic prospecting to detect karst caves, voids, faults and fractured rock zones and time domain tunnel induced polarization for detecting water bodies ahead of TBM excavation faces (Fig 1). Automated data acquisition is recorded via remote control and presented to TBM operators in a graphic visualization mode. The technique and system has been applied over 1,300 times on 21 TBM engineering projects without missing any major geo-disaster sources.

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New line brings new experiences for

Bangalore Metro

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cutterhead is fitted with knife bits that to prove that large diameter TBMs can 9.5m o.d.

TBM drives for inthe Line anddiameter Line 15headings sectionsinofcomplex The development of low carbon concrete is an urgent and can be switched out for disc cutters bore 16 large the contract.

This is one of the largestand diameter associated process, as it is well established that concrete, harder conditions.

The machine design geology difficult segmental ground conditions. includes alinings manlock for cutterhead there haveper been diameter, with seven large 2m Recently wide segments ringlarge ever as the second most used construction material after interventionstoand bars inside machines that have failed, usemixing steel fibre alonethe as thenon-Robbins reinforcement.” water, has an exceptionally high carbon footprint in the excavation chamber. including on the high-speed railway in production of cement and in the application of concrete. As To convert to hard theof initial Bilecik,contracts so this project will demonstrate to It was soonrock aftermode, award for the Grand a first phase, the potential to reduce the carbon footprint mixing bars Paris and initial portion that of theSociété screw du the Grand Turkish Paris, tunnelling Express theindustry client that of large of concrete by replacing steel rebar reinforcement with conveyor can be optionally retracted and diameter machines are up to the challenge.” the mega-project public infrastructure investment, began on the cutterhead, the EPB knife bits are The Eşme-Salihli tunnel is part of the steel fibre reinforced concrete (SFRC) was positive but the explore the use to of the steelAnkara-İzmir fibre reinforcement forproject the for the replaced withtodisc cutters in addition high-speed rail technical assurances for use of SFRC segments for the segmental to replace rebar reinforcement.

“One EPB scrapers are replacedlinings with bucket lips. the Turkish State Railways (TCDD).

The 508km Line 16 Lot 1 metro drives were missing. It has required In addition, of muck areobjectives installed infor line will eventually connect in Ankara the paddles principal Société du Grand ParisPolatlı was to a comprehensive programme of research to meet the the cutterhead to allow the the muck to fall into credentials Province to of Izmir, third most populous optimise sustainability thethe project,” said Société du Grand Paris performance and minimum 100 the muck chute and a hydraulic muck ring city in Turkey, surpassing the IstanbulBischoff, “to maximise respect for the urban environment allows a chute attached to the bulkhead Ankara high-speed railway as the longest year design-life specifications. and reduce as at much as possible theincarbon footprint of the The to move forward and down a diagonal rail line the country once complete. construction. production of the segments for our will Lot convey The Line 16 Lot 1 contract was awarded to Eiffage in angle to allow rock chips toInbethe deposited double-track railway system into the chute and through screw passengers at top of 250km/hr, 1 of Line 16 therethewas significant potential to speeds meet these February 2018 and comprises 19.3km of underground conveyor onto the TBM belt conveyor. To completing the journey between the two keep up production rates in both modes, the cities in 3.5 hours, a journey that would lurry and EPB TBMs are again going head-to-head 1 Robbins two-speed torque-shift gearbox for normally take 6.5 hours by car. n in Bangalore, India, excavating the underground cutterhead rotation is used to enable efficient alignment of the city’s new metro line. More than boring in hard, mixed, and soft ground.

References 10 years ago, contractors of the underground sections “I am very happy that the TBM has • Robbins XRE TBM developments

XRE cutterhead can convert from soft EPB to hard rock configuration; Robbins field service personnel with the assembled machine

• Smart safety for Seattle underground highway - May 2018

Automated forward geological prospecting mounted on hard rock TBMs

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“There have been trials and studies in the past and installation of SFRC segment rings in nonpermanent, nonpublic areas of metro projects,” said Jean-Luc Bischoff of Eiffage, “but not until now has a thorough investigation of steel fibre reinforced segments been A 40kg/m3 dose of steel fibre into the concrete mix for precast segmental progressed to convince designers, clients and linings reduces by more than 50% the required comparative 85kg/m3 of contractors to pursue the large scale application traditional rebar segment reinforcement and provides a fibre network of of the technology for permanent full life cycle 10,000km/m3 structures in France. We are now into the fourth year of working with the SFRC precast segmental objectives by using steel fibre as an alternative to rebar linings on our €1.84 billion Grand Paris Express Line 16 Lot reinforcement. The expectation was to reduce the amount andEPB themachine. experience is confirmation that SFRC operates as1 incontract any typical launched and has advanced more than of steel required per cubic metre of precast lining and The screw for features a replaceable in gneiss to andstay. mudstone,” said Yunus segmental liningsinner is here500m in France Through capture the benefits that steel fibre creates less carbon liner and replaceable carbide bits Alpagut of ATES, the Robbins subsidiary in our research and ware development programme, 100% SFRC is for abrasion protection. A mixed ground Turkey. “This is an opportunity for Robbins pollution in its manufacture and transportation.” the reinforcement of the segmental lining for the 12km of

Crossover machine launches in Turkey

Fig 1. Main structures of the 24km long 16-lane highway sea link December 2022 Inset: The new Shenzhen-Zhongshan sealink highway in relation to the Hong Kong-Zhuhai-Macao link

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Rigs 1, 2 and 3 of the mobile pregrouting equipment

• TBM projects fuel refuge chamber demand - June 2015

seabed is improved or removed and the selected fill of suitable Direct

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April 2022

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The dry powder fire suppression system in the engine compartment and dry powder fire extinguisher on the vehicle were said to comply with the BS6164:2019 Health & Safety in tunnelling in the construction industry regulations, but that no specific discussions were held by TunnelTalk reporting the construction JV and 9.98m diameter dual-mode TBM designed and the vehicle supplier as to what the by regulation should manufactured in China CREG has startedinclude or how the retro-fitted system should operate. excavation of the 6.7km twin tube section of the Cefalù to Castelbuono railway project in Sicily.

The All the MSVs, multi-service vehicles, on the Align JV project, awarded to Toto Costruzioni Italian contractGenerali run on by HVO and all were inspected thoroughly rail company Rete Ferroviariaand Italiana, is another in upgraded as link required.

Discussion on the use of HVO in themasterplan tunnelling to industry and the appropriate fire the European Union TEN-T connectivity suppression systems therefore required are now part improve passenger and freight rail services between of current discussions within the BSI British Standards Scandinavia in the North to Sicily and Malta in the South Institution in the UK and in CEN, the Comité Européen de via the Fehmarn Belt immersed tube linkEuropean between Committee for Standardization, Normalisation, Denmark and Germany and that the Brenner Base Tunnel are preparing and revising applicable standards for and theItaly. application of MSVs in the underground under the Alps between Austria construction industry.

The new 6.7km twin tube TBM tunnel is the largest of three tunnels on the new double-track The 12.3km fire occurred in May 2022 as the PSV was transporting the towns crew tooftheCefalù TBM on one of the twin rail tunnels through rail line between the coastal and thetoChiltern Hills. broke out as the vehicle stopped Castelbuono on the Messina Palermo rail Itroute to pick up a maintenance worker at about 2.6km from (Fig 1). The new double track contract awarded to the portal. When the fire became too fierce for any fireToto Costruzioni Generali forfi€374 runs ghtingmillion efforts, allalmost those with the vehicle left the scene entirely underground and follows a different toportal. Three maintenance crew and walked safelyroute to the the existing single track railon linethe that hugs coast TBM at the about 1.5km further into the drive were ordered to enter one of the refuge chambers on the TBM backup, start up its support systems and stay there overnight until they could walk the 4km to the portal after the fire had burnt out and visibility and the air had cleared.

Shani Wallis, TunnelTalk

Pregrouting combined with double shield TBMs

It is to the industry’s benefit and to the credit of HS2 Ltd and theOf Align that report into the incident is made the JV 36km ofthe 9.9m o.d. (9.1m i.d.) segmentally lined double-shield rock available to excavation the British Tunnelling Society and through it to railway between Oslo TBM required on the twin tube Follo Line andinternational Ski in Norway,industry. nearly 8,000m or 22% required pre-excavation the wider The experience and systematic the to shared lower the andregulations ground water levels in the host lessonsgrouting learnt are sopore that pressure vital safety geologycan andbeprotect against the surface and standards revised as necessary andsettlement for all to that alteration of the groundwater table can induce. This detailed review of the pregrouting appreciate the value of well-devised and well-rehearsed operations developed, optimised and applied by the Acciona Ghella JV life safety emergency procedures in during the project ispractices extracted and from a paper presented

by Acciona at the tunnelling and underground 2020 WTC World Tunnelconstruction.

Congress, Malaysia.

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Burned-out PSV that was too damaged to provide an exact cause of the fire

TunnelTECH A leap forward for SFRC segmental linings in France

Shenzheng-Zhongshan mega sea link

November 2022

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of Lines 1 and 2 made different decisions in choosing their TBM systems. The east-west Line 1 team selected slurry TBM technology from Hitachi of Japan and the team on the concurrent north-south Line 2 selected EPBMs from Herrenknecht, Germany. The fortunes of both were marked, with one of the slurry machines and a replacement EPB machine, having to complete the final much-delayed drives on the north-south Line 2 alignment.

wave information. The velocity analysis and migration methods are adopted to calculate the distribution and imaging of faults, fractured zones and other anomalies.

Shucai Li, Bin Liu, Lichao Nie, Yong Li, Xinji Xu, Zhengyu Liu, Lei Chen and Yuxiao Ren of the Shandong University, China geological forward-prospecting technique was applied 139 times and successfully detected 61 major water-inrush sources.

As an example, the TIP detected a low resistivity area and the seismic method identified a strong reflection (Fig 2).

As a result, a large-scale water-bearing structure about 20m ahead of the tunnel face was successfully recognized. The construction routine was adjusted in time to deal with the 1,500m3/hr of waterinrush that was revealed by advance of the excavation to ensure safe construction.

The TBM operation, as assisted by the technique, was safeguarded and the tunnel project was completed nine months ahead of the anticipated schedule.

On the Gaoligongshan highspeed railway tunnel project in Yunnan Province, the TBM was expected to tunnel through 19 faults and several strong-weathering zones that present high risks of water-inrush and collapse. The automated geological forward-prospecting technique on the TBM was used 98 times and detected 43 sources of potential geo-disaster.

On one occasion, two fractured zones ahead of the face were identified (Fig 3).

The first detected fractured zone was verified by the advancing TBM excavation.

Subsequently, although the rock condition became slight better, the second fractured zone was revealed at the rear of the detection range. The two fractured zones

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Time domain Tunnel Induced Polarization (TIP)

Consisting of a measuring electrode array installed on the cutterhead and current supply electrodes installed on the shield and tunnel sidewalls, the time domain TIP detection technique can image water bodies within 30m ahead of the cutterhead. Driven by hydraulic cylinders, the electrodes can reach out and achieve electric field transmission and measurement automatically under the control of the host computer. The new observation mode with excitation and moving current electrodes improves the detection range to 30m ahead with water bodies imaged by data inversion.

Actual applications

Of the more than 60km of on-site applications, installation on the fourth section of the Yinsong water supply project in Jilin Province, China, was for a 7km TBM drive through limestone with a high risk of water inrushes. The automated

Fig 1. Mounting of the prospecting technique on a hard rock TBM

Seismic Ahead Prospecting (SAP)

There are 10-16 vibrators installed on the upper deck of the TBM about 50m from the tunnel face. Seismic waves can be excited by servo control of hydraulic vibrators with the reflections recorded by 10 to 16 geophones installed on the tunnel sidewalls.

The observation system has offsets in the tunnel axial, vertical and horizontal directions, to collect a wealth of seismic

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Shani Wallis, TunnelTalk

August 2022

For the current new line, the client, the BMRC (Bangalore Metro Rail Corporation), was again reluctant to specify a method for application in the diverse, mixed geology of Bangalore for risk management reasons, specifying an excavation method exposes the owner to claims from the contractors should the specified method prove wanting.

With the selection left to the three current contractors on the new north-south line, one has selected four slurry machines from CRCHI of China, another has selected two EPB machines from Herrenknecht, manufactured at its

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Follo Line

Fig 1. Phase 2 of the Bangalore Metro includes 14km of twin tube underground alignment with 12 new open-cut underground stations

high speed railway line

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SPECIAL EDITION FOCUS: GROUND FREEZING FROM THE EDITOR’S DESK

...the answer is - freeze it

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hether it is saving a roadway heading under a fjord in Norway or protecting vital and vulnerable surface structures and underground infrastructure in the zone of influence in Boston, New York or Singapore, the application of artificial ground freezing is one of the indispensable geological support techniques available to underground engineers and contractors. As the case studies in this Special Edition of TunnelTalk illustrate, success of the projects involved would have been practically impossible without the fascinating method of applying a naturally occurring environment in a region of permafrost, to the ground water present in a soft ground construction operation in any region of the world.

In most of these Case Study articles, the engineers involved repeat that it is the ability of the technique to provide the confidence needed both among the owner of the projects, the contractors involved and most importantly the third-party owners of nearby, adjacent or overhead infrastructure and buildings. The freeze operation applied to rescue the investment of the road tunnel under the Oslofjord in Norway is perhaps the most significant of the Case Studies in that it was selected as the only possibility of completing the last section of the excavation, that the water to be frozen was salty seawater and that any failure of the freeze would be catastrophic with the sea above flooding into the heading and all would be lost.

While it is a method that has been used to impressive affect for many decades, the use of artificial ground

freezing has grown in popularity in more recent times and its application has expanded to include excavation of shafts, cross passages, and to create large underground water barrier walls. In this time, while the basic theories and mechanics of the method have not changed, the technology has advanced significantly in the development of numeric modelling for heat transfer and structural analysis, more powerful and efficient refrigeration plants and new concepts in instrumentation, monitoring and management of the freeze regime. A new generation of engineers, project managers, academics and researchers have emerged and continue to advance the technology.

A conference in London in October 2023 brought together engineers involved in the design, application, and excavation of underground space supported with temporary ground freezing control. During the three-day event professionals share the latest in developments, achievements and concerns including the specialized site investigation and testing measures required for frozen soil applications. The programme of presentations and papers at the conference is on its website and TunnelTalk will attend and publish a post-conference report to share the major findings in the development of this indispensable excavation support technology. n

Shani Wallis, TunnelTalk Executive Editor

Ground freezing to assist Hallandsås through Mölleback Freezing under the sea rescues Oslofjord highway tunnel Deep shaft freeze operations in Milwaukee Box jacking on a grand scale Micro assistance for macro underpass projects Ground freezing supports NATM under historic Boston buildings New York calls on freeze to aid East Side Access advance Collapse of freeze assisted TBM drive at Rastatt Ground freezing assistance under the Suez Canal First application of ground freezing in Singapore Brenner Baseline relies on frozen Isarco River underpass

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Ground freezing to assist Hallandsås through Mölleback After years and many attempts of battling extreme geological conditions, efforts on the famed Hallandsås railway project in Sweden were beginning to succeed. Drill+blast excavation, pre-excavation grouting, and TBM drives supported by ground freezing to get through the Mölleback Zone, were all required to finally arrive at completion.

CASE STUDY AUGUST 2010:

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n Wednesday 25 August 2010, the 10.6m diameter Herrenknecht TBM working on the Hallandsås railway tunnel broke through into a reach of drill+blast excavation to complete the first of the twin tubes. The breakthrough closed out nearly four and a half years of continuous round-the-clock work to complete the 5km segmentally-lined TBM tunnel between 1.5km and 2km of drill+blast work from the north and south portals respectively (Fig 1). The TBM was then dismantled and

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withdrawn from its in-tunnel breakthrough, and returned to the face of the south portal drill+blast heading to repeat the process for the parallel tube.

“This is a great day for everyone working on the project and a major step towards eliminating the greatest bottleneck on the West Coast Line,” said Per Rydberg, Project Director at the Swedish Transport Administration on the occasion of the celebrations.

Surrounded by frozen ground in the pilot tunnel

The twin tube, double track rail tunnel had been under construction since the early 1990s and has overcome serious geological, political, technical and environmental setbacks. Controlling ground water and working through exceptionally difficult geological and logistical conditions charted construction of the Hallandsås project.

Work started back in the early 1990s when an open hard rock machine was procured and assembled but abandoned after only some 10m as being unsuitable for the job. In 1996 a new contract was awarded to Skanska for a drill+blast operation on four headings. This advanced for about 1.5km from the north portals and about 2km from the south before it too was terminated over an environmental issue.

The toxic Part B of a two-part chemical grout being used to control water ingress ran freely from the tunnel heading and contaminated local water ways, poisoning wildlife and cattle drinking from the rivers and creeks. All work was suspended and a remediation contract was then let for the years 19982000 to line the drill+blast lengths of tunnel and hold all secure while the client, the Swedish National Railways, and the Government decided the fate of the project.

In 2003 it was decided to let another contract to Sweden’s international construction company Skanska with French company Vinci Grands Projets for a new TBM attempt, this time using a closed pressurized system with a precast concrete segmental lining.

The one new 10.6m o.d. Herrenknecht TBM started from the end of the drill+blast heading at the south portal in early 2006 and worked pretty much 24 hours/day, 7 days/ week since then to connect to the 1.5km of drill+blast tunnel from the north portal in August.

Tight restrictions imposed on the project by the Swedish Government’s environmental protection agencies to

control ground water flows from the headings limited excavation to only one tube at a time.

The 10.6m o.d. Herrenknecht TBM being used to tackle this attempt to conquer the Hallandsås challenge is designed to withstand 15 bar in the static mode, 8 bar in continuous dynamic mode, and 13 bar for short stretches of a few meters in dynamic mode. “Almost 95% of the tunnel is in hard abrasive rock but it is highly fractured and the high water content results in high volume water ingress at high pressure,” said Sturk. “We used the machine in the closed slurry mode for a time at the beginning but the wear on the cutterhead and the demand on the systems was very high, so we have instead progressed mostly in the open mode with extensive pre-grouting to control the water. The Herrenknecht TBM is fitted with the ability for extensive grouting ahead of the tunnel face to provide a treated zone into which an advance of five to ten 2.2m wide rings of precast lining can progress before the grouting cycle starts again.”

This method served TBM progress well through the 5km advanced from its start at the south end of the tunnel, but it was not considered capable of controlling the water content in the essentially flowing materials of the Mölleback Zone (MBZ). Here the more effective pretreatment of ground freezing, installed horizontally from a pilot tunnel, was adopted.

Measuring 250-300m, the Mölleback Zone (MBZ) of the 8.6km long tunnel is a tectonically faulted zone of highly variable and altered rock with a high ground water content. “The zone is made up of thin layers of different types of weathered rock and soils all lifted vertically,” explained Dr Robert Sturk, Technical Manager for the Skanska-Vinci HB construction joint venture. “A high 5

“This was a truly significant achievement,” said Sturk. “We then had about 600m to go to break through completely by about mid-September for the first tube.” The first TBM hole through was achieved ahead of the anticipated midSeptember 2010 date and with the worst of the unknown now largely behind them, the second drive could come in earlier than programmed in September 2013.

The 10.6m o.d. TBM worked through long sections of highly abrasive and fissured rock (mainly gneiss and amphibolite), with rock strengths of up to 250MPa. Best dual-mode TBM rates were achieved in open mode, although time-consuming grouting and frequent maintenance shutdowns to cope with high cutterhead wear maintenance and tool changes, limited speed.

After the first breakthrough into an in-tunnel drill+blast cavern, the highly worn cutterhead was replaced and larger 19in disc cutters were installed. At final breakthrough of the first tunnel, some four and a half years after machine launch. The machine was completely refurbished, and again equipped with a new cutterhead for excavation of the second 8.6km long drive, which started in early 2011.

After predictably better progress, final breakthrough of the parallel drive came some two and a half years later in September 2013.

Final breakthrough at last!

water table in the 130-140m of cover produces water pressures of about 11-13 bar at the tunnel horizon.”

Knowing the risks of the MBZ ahead of them, the construction team decided to drive an in-line pilot heading of about 600m from the face of the north portal drill+blast headings to the start of the MBZ and from there install the 100m of full-circle ground freezing. With the ring of freeze pipes set at an 8m diameter profile within the 10.6m o.d. profile of the TBM, a new system of glass-fibre freeze pipes was developed by the joint venture and specialist Austrian drilling company Insond so that the TBM could grind through these as it progressed.

The various phases of installing the freezing through the MBZ started in January 2006 (Fig 1). By the time the TBM arrived, a collar of frozen ground about 4-6m thick around the 8m diameter circle of freeze pipes was in place. The freezing circuit was discontinued in midMay and it took 14 days, working around the clock, to get through the zone and achieve breakthrough with the pilot heading.

As the machine progressed through the frozen zone, cutting through the glass-fibre freeze pipes as it advanced. For the last 600m, the 10.8m diameter TBM excavated the collar of rock that surrounds the central pilot heading, breaking through into the completed drill+blast heading.

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Completing the Hallandsås rail tunnel, no matter its technical challenges and financial costs, was vital to the operation of rail services in Sweden. The country’s important West Coast Line is currently 85% double track.

The sharp curves on the single track over the Hallandsås ridge constituted a serious bottleneck. With the double track through Hallandsås is completed, a doubling of rail freight will be possible, and the number of trains per day can increase from the current four to 24 per hour. A double track railway is said to correspond to a 16-lane highway in capacity.

“Getting through this MBZ zone was one of the high risk elements on the project,” confided Dr Terry Mellors, adviser and monitor of the project for its insurers. “To have come through successfully was a benchmark achievement technologically, and an outstanding milestone for the project.”

Driving through the frozen zone was said to have been highly successful according to Sturk. “Of course there was still considerable risk involved - the effectiveness of a freeze can never be guaranteed - but it proved to be very secure. There were no incidences of serious concern. We will now repeat, basically, the whole routine to complete the second tube.”

“This breakthrough is an absolutely great moment in my life,” said Martin Herrenknecht at final breakthrough in September 2013. “High levels of co-operation between all project partners safely completed a tunnel project that once seemed impossible.”

Hallandsås is among the benchmark projects in the development of TBM technology to work under high ground water content and high ground water pressures.

The Herrenknecht machines designed for the Arrowhead project in California began this cycle of development and the Herrenknecht system procured for the Lake Mead water intake tunnel project in Nevada was next in the evolution of the technology. n

CASE STUDY DECEMBER 1999: In December 1997, excavation of the 7.2km long road tunnel

under the Oslofjord in Norway was stopped by a 15m zone of loose glacial moraine deposits at the bottom of a deep undersea channel. A bypass allowed tunnelling to continue around the offending zone but excavation through the zone could only advance from within the safety of a 3m wall of -28°C frozen ground to complete the project. Shani Wallis of TunnelTalk visited the project to know how this application of ground freezing was accomplished.

Freezing under the sea

rescues Oslofjord highway tunnel

T

he 7.2km long Oslofjord highway connection passes a maximum 130m below sea level beneath the bottom of the fjord with a maximum overburden of 80m to tunnel invert and a maximum 50m water depth.

The tunnel is part of the new 26.5km long two-lane connection on the E18 Highway which will allow through traffic from Europe and from the south and west of Norway to bypass the city of Oslo at the top end of the fjord (Fig 1).

There were several options for the crossing including a high bridge spanning the islands further into the fjord.

But environmental, social and political opposition to a bridge, despite its potential as a 'Golden Gate' of Norway, carried sway and the subsea tunnel, with the lowest cost estimate of the options, was selected.

Norwegian tunnellers are well experienced in the design, investigation and excavation of subsea tunnels. The Oslofjord connection is the 19th subsea highway tunnel to be constructed and there are still further candidates for fixed fjord crossings in the country's efforts to replace the costly and weather-dependent ferry crossings in

the national highway network. Norway can rely on its good quality metamorphic rock but site and geological investigation is thorough and particularly in areas of suspected weak zones.

For the Oslo crossing particular investigation was undertaken for a narrow channel between the west portal landfall and a small island just 500m offshore.

Seismic survey, indicating a major fault in this area, led to the decision to use core drilling to investigate the rock cover further. Two diagonal core holes were drilled into the rock from each side of the channel (Fig 3). Using sophisticated directional drilling techniques developed and used by Norway's oil exploration industry, the holes were guided to cross each other at about 120m below the bottom of the channel and within the zone of the proposed tunnel alignment. In addition to core recovery, hole-to-bottom seismic survey was also carried out from the drilled holes.

“From these investigations we knew that the zone at the bottom of this channel would be weak," explained Fridtjof

Fig 1. Plan of the new 26.5km long highway connection under the Oslofjord

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Fig 2. Geological section of the 7.2km Oslofjord crossing, with the difficult underpass highlighted

Fig 3. Alignment of the two core hole borings undertaken from the mainland and the island either side of the deep glacial channel. Both cores intersected the lower part of the main tunnel alignment and failed to identify the loose sand and cobbles of the glacial channel just meters above in the upper half of the tunnel. Seismic surveys also wrongly indicated a 30m cover of sound rock above the tunnel

Andreassen, Tunnel Project Manager for Norway's Public Roads Administration (PRA), the client. “We could have continued taking three, four, five or more core holes but we believed that we had sufficient information to know that this section would require special treatment during excavation, including consolidation grouting and installing the final in-situ concrete lining immediately behind excavation. The biggest surprise was that, when we tried to stabilise the area with cement grout, the effort was totally ineffective. More drastic measures were required if we were to come through this zone."

Tunnel excavation

The full 26.5km long highway connection, with its six tunnels totalling some 12km, is split into four contracts:

Contract 4, the Oslofjord tunnel, was won in March 1997

by SRG, the Scandinavian Rock Group, which also won Contract 3 with two further tunnels. “We started work on site in April 1997," said Stein Schanke, SRG's Site Manager for Contract 4. "We started three headings, one from the east portal, and two in each direct from a 730m long adit at the sea front on the west side of the fjord.

Homes close to the alignment at Verpen dismissed the tunnel's east portal as a working access."

Schanke explained that work progressed very well at the start. The full 80m2 tunnel face was being excavated by drill+blast in rounds of about 5.4m and excavation was progressing according to programme and without particular problems.

Fig 4. Cross section of the new three-lane tunnel with its longitudinal ventilation and polyethylene foam drip shed cladding lined with a layer of wire-mesh supported shotcrete as a fire retarding coating

To limit the length of the subsea crossing, the tunnel on this otherwise two-lane bidirectional roadway has a steep 7% gradient. Three traffic lanes are therefore required, one going downhill and two on the uphill slope in each direction, the second lane on the upgradient for heavy trucks and slow-moving vehicles (Fig 4). The construction access adit on the west side landfall will be a permanent escape route from the subsea tunnel.

"It was from the east bound heading from the east side working adit that the weak zone was first encountered by a probe hole," said Schanke. “Systematic probing is an accepted essential part of subsea tunnelling in Norway and we were drilling three 30m long probes in the crown with a 15m overlap. It was soon after the 15m overlap with the previous

8

probe that the new probe struck water at enormous pressure and we knew we had intersected with the full hydrostatic pressure of the 130m head of the fjord above us. We stopped immediately and the discussions of what to do began."

Grouting was to be the planned solution for progressing through this zone but initial attempts to inject grout and seal the zone had no effect. In fact, more than 700 tonne of cementiteous grout was pumped into the zone but without the slightest effect in cutting off the water ingress or reducing the water pressure.

Shortly into the grouting phase it was realised that the zone could hold up progress on the tunnel for some time. Further investigation of the area illustrated that the top third to 50% of the tunnel had run into the loose glacial moraine at the bottom of the fjord with hard but fractured rock prevailing in the lower half.

Early discussions about realigning the tunnel to go down deeper beneath the channel were dismissed quickly.

"The tunnel is already on the maximum 7% gradient and to maintain a reasonable slope we would have to go back a long way to start the new gradient," said Schanke. ''This was too expensive and time consuming."

It was also impossible to go around the zone as the deep glacial channel - cut, it is believed, by a glacial meltingage river - extends the full length of the fjord.

With sound rock beneath the zone, it was decided to excavate a lower bypass tunnel, spiralling away from the main tunnel alignment, passing some 20m under the glacial channel and rising to the main tunnel alignment on the other side about 100m from the zone (Fig 5). ''From here we were able to continue east under the fjord to meet the heading from the west as well as work back towards the trouble zone," said Schanke.

The ability to excavate the bypass tunnel is agreed by all as the real saviour of the project. ''The bypass allowed excavation of the main tunnel to progress according to programme and without being held up by the bad zone," said Andreassen, ''and excavation of the bypass is not wasted as this will become the tunnel's drainage sump, replacing the original 140m long or 7,000m3 excavation designed to provide this facility."

"With the bypass we were able to advance the eastbound heading and actually achieved breakthrough under the fjord in February 1999, some six or seven weeks ahead of schedule," said Schanke. The 2km drive west from the construction adit on the east side broke through on programme at the Verpen portal in October 1998.

This section has been finished with the water and frost protection lining and road deck and was handed over to the owner for M&E finishing works in September 1999.The section from the east portal is also nearing completion and is scheduled to be handed over to the owner by May 2000. “This left us with just this 46m which includes the 15m bad zone to finish and we should be able to complete the contract in Summer 2000."

Ground freezing

On reaching the difficult zone, when both grouting and ground freezing were being considered as possible solutions, Anne-Lise Berggren, founder of the Norwegian company Geofrost Engineering, was consulted regarding the freezing option. "Freezing was obviously a solution," said Berggren, "even in these permeable conditions and under such high water pressures. The challenge would be accurate drilling through these glacial deposits which include boulders of very hard rock in a sand/gravel matrix with very little to no clay, and under the high water pressure."

Having stopped tunnelling at the zone in December 1997, and after realising that grouting was having no effect, the

Fig 5. The valuable bypass tunnel runs just 20m beneath the elevation of the main tunnel alignment through competent rock and is supported with only shotcrete and rock bolts. As the lowest part of the excavations, the bypass becomes the main tunnel‘s drainage sump replacing the original sump excavation

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Fig 6. Design of the thick, heavily reinforced concrete lining installed as part of the excavation cycle through the frozen zone

Freezing would be installed from the eastbound heading from the east mainland access adit and excavation would progress back from the other side of the 46m zone toward the west portal using the bypass tunnel for access (Fig 5). The programme started in the west side of the zone by enlarging the tunnel to create a 20m long x 220m2 freeze-installation working site. This also provided the collar into which the first row of 53m x 30m to 40m long freeze-pipe holes drilled in a cone array around the full tunnel profile including across the invert.

Drilling with high water pressure drilling equipment was used to drill the freeze holes and special packers were used to prevent drill-hole blowouts under the high water pressure. Brødrene Myhre and Båsum Boring were the engaged drilling subcontractors and the Devico surveying system was used to check the accuracy of each hole.

While drilling progressed, laboratory tests of the moraine material were also underway.

The material retrieved from the drill holes was frozen and the mechanical properties studied.

"The test results showed much lower strength parameters than originally expected due to the salinity of the pore water," said Berggren.

"We needed either a colder or thicker freeze zone to provide the necessary pre-support through the soil. Of the two, we chose to install a colder freeze zone to take the temperature below the -21°C eutectic point of salty water.

To achieve this we needed a second row of freeze holes in the upper half of the tunnel profile through the moraine material."

A 3m thick wall of frozen material to -28°C was calculated to be the requirement, to support the zone during excavation and include a sufficient margin for safety. The second row The final lining reinforcement cages are pre-fabricated before being of 28 holes in the moraine material in the erected in the next concrete lining pour crown zone were drilled inside the first set of holes and as close to the tunnel's excavation decision to adopt the freezing solution was taken in April profile as possible. This extra row of holes increased the 1998 and a NKr 10 million contract, including drilling, was original NKr10 million contract with Geofrost and freezing signed with Geofrost. of the zone using a brine circulation system designed for -40°C started in May 1999.

In preparing the freezing design, it was calculated that the freeze wall in the crown would have to support a total load Stein Schanke of SRG had had experience with of approximately 1,400kPa comprising the 1,200kPa of the freezing before on the road tunnel beneath the streets 120m hydrostatic load, or a 12 bar pressure, plus about of Olso City in the early-1990s where Geofrost was 200kPa for the 80m of material overburden. "At that time, and also the engaged specialist freezing contractor. On before we had conducted laboratory tests on the moraine that occasion, the water was under 45m of hydrostatic material collected from the initial freeze-drilling holes, our pressure, was also much less salty and freezing expectations were that a freezing temperature of -10°C was into a material with a higher clay content. The would create the necessary freeze support," said Berggren.

Oslofjord freezing operation was to be an entirely "We started therefore with a circle of 51 freeze holes around different undertaking. the perimeter of the tunnel's excavation profile."

The original expectation - after grouting but before the In addition, the in-situ concrete lining would advance drilling experience and before laboratory testing of the with excavation. This is also designed to carry the moraine material - according to Schanke, was that the full hydrostatic and material overburden load and is last 46m section of tunnel would take about six months therefore substantial. It is heavily reinforced with 280kg/ to complete from the time the decision to use freezing m3 of steel and is up to 1.2m thick (Fig 6). The freezing was taken. In fact it will have taken nearly two years, with design allowances were made for the concrete's 70°C completion expected in December 1999. curing temperature as well as the heat generated by the A major reason for taking much longer than anticipated immediate shotcrete applied to seal each exposed round was to complete the drilling phase. First there was a lot of of frozen rock and moraine.

10

steel left from the difficult grouting operation. Secondly the rounded stones and hard boulders in the glacial deposits and the high water pressure created difficult drilling conditions. A water hammer was used for the first time in soil conditions to overcome water pressure problems.

With the extra 28 holes in the moraine material and the two freeze pipes in the middle of the tunnel profile, the freeze drilling pattern totals 83 holes. In addition there are 17 survey holes to monitor the temperature. Drilling started in Spring 1998 and took until Spring 1999 to complete. Only 11 holes in total were rejected.

Another reason for taking longer than anticipated, was that the material, as tested, required a much colder temperature than originally expected and it has taken time to achieve that necessary temperature. “The ground water is almost still, there is not much velocity at all,” explained Trond Egeberg, a senior engineer with Geofrost, “but the water is very salty and this requires very low brine-circulation temperature, as low as -40°C, to achieve

a hard enough freeze zone. At the moment, (during a visit

by TunnelTalk to the site in May 1999 following the World Tunnel Congress in Oslo) we have a temperature of about -20°C in the freeze wall and we need at least -28°C.” Eventually, the necessary freeze was achieved, and the decision to restart excavation was taken in August 1999.

As was always the plan, the in-situ concrete final lining would progress with excavation. The excavation cycle was therefore based on one 1.5m to 2m blast per week with layers of shotcrete up to 20cm thick in the crown applied immediately to protect the exposed frozen soil, and the final in-situ concrete lining cast in two stages; first the theoretical 1.2m thick invert slab, followed by the theoretical 1m thick arch cast behind a 5m long form. To provide the final three-lane clearance and accommodate the 1m to 1.5m thick lining, the profile through the frozen zone was increased from the normal 80m2 cross section to 130m2. The reinforcement cages for the lining were prefabricated and erected into the concreting bay to accommodate the one blast per week cycle. The arch is

Freezing installation The setup required to accomplish the freeze wall in the Oslofjord link is a major operation in itself. The illustration indicates the different types of equipment needed to establish a freeze including the ammonia plant, the heat exchange system, the temperature monitoring station, the brine circuit and the cooling water cycle.

“We are using approximately 330kW of electric energy to maintain the freeze,” said Anne-Lise Berggren, Director of Geofrost who founded the company in 1986.

Geofrost has undertaken several freezing contracts in Norway as well as in Sweden and more recently in Hong Kong.

small temperature difference in the return brine flow.

This heat must be dissipated in steps via cooling water and by air. Release of the heat into the air must take place some distance from the working area and we have a 500m long x 1.8m diameter ventilation duct delivering 90m3/sec of air leading away from the water/air heat exchanging unit into the tunnel toward the Verpen tunnel portal.”

Having established the freeze wall, it will be maintained until the soil zone is excavated. The inner row of freeze pipes will be disconnected first when they intersect the tunnel profile, and the rest will be disconnected before the last section of blasting through the 10m barrier of good rock on the Verpen side.

In the circulation system of the Oslofjord installation, only two freeze pipes in the upper moraine zone are linked to one return cycle. In the lower part of the tunnel, Once the freezing system has been disconnected it through more competent rock and where only water will take several months for the ice barrier to melt. The sealing is required, three pipes are linked to each return concrete lining will then be the only barrier to the loose cycle. The Oslofjord installation is a closed pressurised moraine material and the 130m water pressure of the circulation system, rather than a system with an open fjord above in this section of the operating road link. brine reservoir, because the freezing plant is lower in elevation The freezing installation, illustrating the main components of equipment and their location within the enlarged freeze installation working chamber than the freeze holes.

The brine is pumped around the system at a reasonably fast velocity. ‘’The velocity is required to limit the temperature difference between the in-going brine and the return flow to only a few degrees centigrade,” explained Berggren. ‘’This is needed to help maintain a uniform freeze across the zone. But in reducing the ground water temperature from its natural 10°C to the frozen temperature of -28°C we are generating about 500kW of heat energy. The brine circulation system is about 15 to 20m3 in volume and it is this volume flow that gathers the heat from just

11

Thick frost crusts around the brine freezing circulation pipes as they disappear into the zone of glacial moraine to freeze and stabilise the loose material with a wall of -28°C ice

poured the day before the next blast which started the next weekly cycle.

The in-situ concrete lining was installed to within 70cm of the frozen tunnel face leaving very little space for working the next heading. Handheld drilling equipment had to be used to drill some of the 243 charge holes and seven cut holes in each 120m2 face. Special cartridge explosive, developed specifically for the project by the Norwegian explosives experts Dyno Nobel for application at such low temperatures, charged the face. There was one cartridge of explosive at the bottom of each hole to initiate the blast, and bulk Anolit was pumped in to fill the remainder of each hole.

In addition to special explosives, the site is also using newly developed electronic detonators developed in Germany. These are microchip controlled with the delays programmed individually to achieve the smoothest of blasts and at very low ppv. “Smooth blasting and low peak particle velocities are needed to protect both the integrity of the freeze zone and the installed freeze pipes," said Schanke.

"The most exciting part of the process, other than getting started again," said Schanke, was to expose the glacial moraine, to see what it looks like and know what it is like to drill. We are now (mid-October during the second visit

by TunnelTalk to the job site) two blasts into the zone and

From left: The 3m x 3m door in the massive steel/concrete composite wall installed as ‘insurance’ against a possible but highly improbable inrush while excavating through the freeze zone; The shotcrete covered face of the frozen zone with the charge holes drilled and the formwork of the previous concrete pour just 70cm behind

12

the material is as we expected. The matrix is mostly sand and dirt and the smooth rounded stones are of various sizes and covered with a skin of the ineffective grout. The bottom section of the zone is moraine material and the top section is glacifluvial material. The freezing is holding very well and we have not had to change our pre-planned method of getting through this difficult zone."

The most critical part of the excavation cycle, according to Andreassen, is the 70cm overlap between the last concrete arch and next drilling cycle. This 70cm section effectively remains 'open' for two weeks. “The freeze wall extends to about 10m outside the tunnel profile," said Andreassen, "but when you stand at the frozen face, beneath this 70cm overlap zone, it is something to think that it is only a wall of ice protecting the safety of us and of the tunnel from the 130m of the fjord above. This two-week 70cm 'opening' of the frozen soil between the concrete casting phase and the next blast equals the frozen material's minimum stand up time. In essence, the -28°C x 3m thick beam of ice over the crown of the tunnel must be able to take the full load - which obviously it is doing."

The biggest risk to the operation, all agreed, was the possibility of a water seepage event, which, if significant enough, would be unstoppable and would lead to failure of the ice barrier and an inrush, over time, of the loose glacial moraine and a flood of high pressure water. One potential problem within the frozen zone, according to Andreassen, is shear pressure in the ice which could create a leakage crack and initiate seepage. Another, according to Schanke, is the fact that immediately on being exposed to the air, the temperature rises and the frozen rock of the tunnel starts to melt. This phenomenon is recognised by the crust of frosty moisture condensation that forms on the frozen rock immediately after the blast.

At this point, loose rocks and stones in the frozen moraine could fall out and initiate a ravelling effect. The coating of flash shotcrete prevents any loose stones falling but nevertheless, both scenarios are possible, if highly unlikely, and the site team had to make provisions for such an eventuality.

The 'insurance', as it is called on site, against an inrush is a massive steel and concrete composite wall installed about 30m behind the bad geological zone. This massive 2.6m thick x some 160 tonne structure is designed to take the full 1,400kPa hydrostatic and material load of the overburden. A 3.5m x 3.5m door within the wall is just large enough to accommodate the excavation equipment and is designed to close within minutes. The remaining zone of solid rock provides the necessary barrier on the opposite side of the zone.

"Before each blast," explained Andreassen, “the tunnel and underground environment is evacuated leaving only a senior manager from both the PRA and the contractor; the blasting master; a shift foreman; and a driver of the loader which is hooked to the cable to close the barrier door. It is within the first minutes after each blast that the decision of whether or not to close the door is taken."

Although an expensive item in the cost of getting through this difficult zone, the barrier is, in reality, seen as cost effective insurance. Had there been an inrush and without the barrier, the entire tunnel would have been lost. The flooded tunnel could never have been recovered. An inrush held by the barrier would at least save the tunnel

Project finance and funding

T

he total cost of the 26.5km long highway is NKr 1,306 million or about US$200 million in 1999 rates.

The total cost of the Oslofjord tunnel is NKr 440 million or about US$60 million.

The cost of advancing the 35m through the freezing zone was about NKr 35 million or about 10% of the original NKr 347 million bid price of the tunnel. This is a major addition to the tunnel cost but savings in other parts of the excavation operation, including less support installed than originally envisaged, has controlled overall cost increases. Passing through the known weakness zone was expected to cost about NKr 10-12 million, according to Andreassen.

The overall project has risen from its original startof-construction budget of NKr 1,076 million to the current NKr 1,306 million.

For comparison, the cost of the three-lane fjord tunnel is approximately NKr 60,000/m, including the freezing operation. The cost of a 6km section of the open highway with small viaducts and a short two-lane tunnel is NKr 35,000/m.

The project is funded by a public/private arrangement.

The national government is funding 38% of the cost and a private company has funded the remaining 62%.

This will be repaid from tolls that will be collected for 15 years from 2000 to 2015. When the highway opens in Summer 2000, traffic is expected to be about 4,200 vehicles/day. This is not expected to rise significantly until the toll is removed in 2015. The toll is set at NKr 50/car and NKr 220/large freight-carrying truck.

and allow other options of getting through the last 46m zone. These could include either re-establishing the freeze or realignment of the main tunnel.

"We have not had to close the door so far, although the closing procedure is rehearsed before each blast," said Schanke. "We are now beyond the most critical part of the work where the zone of loose moraine extended into about half of the tunnel face. We have about 25m or 11-12 blasts or 11-12 weeks to go and we hope to hole through in December 1999. Once the road deck is installed we hope to hand over the finished job to the PRA by Summer 2000. This is just a few months later than the original programme and includes delays accumulated on other areas of the work."

Tunnellers around the world envy the Norwegians their strong rock conditions for the majority of their thousands of kilometres of tunnels for hydropower, roads and other installations, but when the good quality rock fails them, the solutions required are often spectacular. Freezing is often considered a very expensive solution-of-last-resort, but as illustrated on the Oslofjord project, freezing proved to be a highly effective and cost competitive method of rescuing the subsea road crossing. Freezing is a valuable addition to the Norwegian subsea tunnelling experience and one that may well be required to solve equally challenging situations in future. n 13

Deep shaft freeze operations in Milwaukee CASE STUDY MAY 1985: In the 1980s, Milwaukee, in the USA, embarked on its $1.65 billion Water Pollution Abatement Program (WPAP) to eliminate combined sewer overflows into Lake Michigan initiating the largest public works project in the history of the State of Wisconsin and one of the largest construction programs in the USA at the time. Part of the program was construction of deep shafts for which ground freezing provided vital excavation support. In a visit to the project in 1985, Shani Wallis of TunnelTalk learned of the fortunes of the freeze operations.

I

n the saturated silts, sands and clays immediately under Milwaukee, the excavation of shafts has not been easy. In the past, several different techniques including dewatering, caisson sinking and excavation under compressed air, have been used with varying degrees of success.

The city’s Water Pollution Abatement Project however involves the deepest subsurface work ever undertaken in Milwaukee going through the entire 170ft (52m) of soft, water-bearing alluvial deposits and a further 100ft (30m) through the limestone bedrock to reach the deep alignments. Dewatering to these depths has been excluded for fear of excessive settlement. Compressed air pressures would have to be too high in order to control the 40psi ground water pressure at these depths and while the caisson sinking method has been used, there have been problems with steel casing and stiffening ring failures. Serious flooding and floor heave has occurred and one caisson attempt had to be abandoned. Ground freezing, rarely used before in Milwaukee, is the most effective method but the geology has presented even this technique with a number of problems.

On the first of three 300ft deep x 23ft 6in o.d. (91.5m x 7m) shafts required, sinking under frozen conditions Installation of the freeze system for the screening shaft

was down to 106ft (32m) when water began to pour in through the central pressure relief hole from an unknown lower source. The flooding shaft was hastily refilled and refrozen at a lower temperature.

Freezing at a lower temperature is not ideal though, as Pat Doig, the Area Manager for Cementation explained.

“Freezing to a lower temperature freezes a larger area of ground, thus encroaching on the soft inner core. In this instance the base of the cylinder had to be frozen right across the shaft to be re-excavated. The frozen ground is extremely hard and has to be picked out using handheld jack hammers. Blasting is out of the question due to the unknown nature of the water source and the risk of damaging brine pipes, which would be disastrous.”

Flooding of this first shaft caused a two-month delay. It is now the subject of a claim and although the cause has not been agreed, Doig explained his theory. “When the excavation was completed to rock, a fissure was found to traverse the shaft. It is possible that water from outside the freeze wall found its way into the fissure below the toe of the ice wall and up through the unfrozen core of the shaft.”

During the site visit, the shaft had been safely re-excavated and taken to the 170ft (52m) deep bed­rock interface, and the in-situ concrete lining was being cast.

To maintain the construction schedule, work on the second shaft had started although Cementation had not intended having two freeze shafts operating at once.

Freezing higher than expected

This contract was awarded to Cementation in August 1984 as lowest of 11 bids at $10 million.

It was 4% below the second bid, and $6.7 million below the highest bid. All estimates were higher than the Engineer’s Estimate of $8.9 million. “This discrepancy is possibly attributable to the client’s lack of appreciation of the freezing technique,” suggested Doig.

“The client did not specify freezing but it is the most effective method and it was on the freezing aspect where we had the edge over most of our competitors. They probably intended to subcontract the freezing work.

We are experienced freeze shaft sinkers with our own equipment and have engaged the specialist Foraky of the UK as consultant.”

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The contract involves the sinking of three 340ft (104m) x 20ft (6m) i.d. in-situ concrete lined shafts and excavation of a 60ft wide x 120ft long x 40ft high (18m x 36.6m x 12m) pumping station chamber (Fig 1). The shafts are about 150ft (46m) apart. The first is a screening shaft where debris in the flow from the deepest interceptor sewer is filtered out. Flow is then conducted into the pumping station via a 10ft (3m) diameter pre-stressed pipe grouted into the rock. From here it is pumped through steel pipes housed in the ingress/egress shaft into the Jones Island treatment plant. The equipment shaft provides access to the pumping station.

Cementation moved onto site in January 1985, joining some 25 prime contractors already working on the congested Jones Island area.

Work started by drilling a circle of 34 equally spaced freeze holes 5ft (1.5m) outside the diameter of each shaft. These were drilled to an alternate depth of 180ft and 90ft (55m and 27.4m). In this way, the top 90ft will freeze quicker and work can start two to four weeks earlier than without them. The lower section will not be excavated for about five weeks so half as many holes over the longer period will establish the freeze.

Once drilled these holes are surveyed since it is vital to know exactly how far apart they are to achieve effective freezing. Surveying accounts for 20 to 30% of the drilling and installation cost. On the surface, the 34 holes are about 3ft apart, but the 17 deepest holes, which should be 6ft apart theoretically, can have strayed off line and be a maximum 8ft apart. If this occurs, some of the shorter holes may have to be extended. In addition, there are two observation holes outside the freeze pipe circle fitted with thermocouples and a 2in (5cm) pressure relief hole in the center of the shaft.

When everyone is satisfied with the hole pattern, the freeze pipes are installed and linked to the freezing plant via a closed circuit of steel and flexible rubber hoses. As there are three shafts to complete, Cementation established a central freezing station where ammonia refrigerants cool calcium chloride brine to -36°F. The freezing brine is then pumped down the inner 2in (5cm) diameter plastic pipes and returns via the annulus between the inner pipe and the outer 4in (10cm) steel casing. Approximately 600 gallons (2,800 litres) is pumped around the circuit/min losing about 1˚F in temperature on its journey.

The refrigeration plant is an electrical machine which runs constantly and energy costs are high. Cementation’s electricity bill is $15,000/month. For this reason, the freezing plant is located as close to the shaft as possible, a maximum 150ft in this case, and all the exposed hoses and

other components of the circuit are heavily insulated, as is the exposed frozen ground as the shaft is excavated. The system is also well protected against damage.

For this reason too, speed is of the essence. It takes approximately one month to drill the freeze holes and establish the brine circuit. Excavation then starts about four weeks after start of the freezing process. Cementation is using a 2yd3 (1.5m3) clam shell grab to excavate the soft inner core. Once out of reach, a Kubota mini excavator mucking into it a 90ft3 (2.5m3) muck bucket takes over.

The last 30ft or so will have frozen completely across and is picked out using the jack hammers.

Working three 8hr shifts/24h day, five days/week, it takes about six weeks to reach the bedrock interface at 170ft below the surface. The in-situ concrete lining must be cast before freezing is suspended.

Bottom lining

To allow excavation to progress as fast as possible, Cementation is excavating and lining the shafts in two separate steps, instead of taking the lining down with excavation, which is more usual. “This results in a more efficient operation and a saving in time and money. It also provides a better quality and a more easily achieved joint between each pour since the previous pour is below rather than above,” said Doig.

Waterproofing seals between the concrete pours was not specified, but Cementation has taken upon itself to fit a 200mm deep waterstop in each joint. “The shafts have to be watertight and this is not an excessively expensive addition but will save us time and money on subsequent patching and pointing work,” explained Doig.

Lining is progressing on a 24hr day x five day/week schedule using a 20ft (6m) deep form. It takes 100yd3 (76.5m3) to fill the form and this is transported to site in 10yd3 ready mixed batches. It takes 7hr to complete a pour. During the curing time the rebar for the next pour is placed. After 8hr, the form is struck and reset. All this work takes place from a triple deck 20ft deep work platform suspended from two static winches. Two pours are completed every three days which completes the lining in two to three weeks. The lining will have a final strength of 4,000psi or 27N/mm2.

During the site visit, lining was progressing well in the screening shaft and the equipment shaft, however, excavation had been suspended temporarily. “Water was seeping through the pressure relief hole and the temperature in the observation holes had risen slightly,” said Doig. “We decided to stop excavation and monitor the situation fearing we may have run across the same fissure as in the first shaft.” This was not so and excavation resumed after six days. Despite these hold-ups, Cementation still

Figs 1 and 2. Elevation and plan of the pumping station and its three associated shafts

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Triple deck platform for concrete lining work on the Cementation contract (left); Bottom of the Dillingham TBM working shaft

expects to finish the 18 to 21 month contract at the end of 1986, three or four months ahead of schedule.

After excavating and lining the upper section of the shafts, they will be lowered another 100ft or so through the limestone to their full 340ft (104m depth). The pumping chamber will then be excavated using drill+blast and the connecting tunnel from the screening shaft to the pumping station will be excavated. Completion of the complex shaft sinking and pumping station contract remained on schedule for later in 1986.

Freezing with a difference

On the neighbouring Crosstown interceptor contract the consortium led by Dillingham started work on site with the sinking of a 300ft deep x 27ft 6in i.d. (91.5m x 8m) in-situ concrete lined access shaft and a 300ft deep x 20ft diameter reception shaft. But as with all the shaft sinking works in Milwaukee, Dillingham found it far from straight forward in the upper water-bearing alluvial deposits. The access shaft, located in open space along side railway shunting yards close to a major highway overpass, was sunk first, using liner plate and steel ribs through the top 45ft of alluvial deposits to the rock.

For the second reception shaft, Geofreeze was subcontracted to sink a freeze shaft using a mobile freeze unit consisting of 30, 60 and 80 tonne machines mounted on a truck to chill the brine to -27°F. The soft inner core was excavated by an unusual piece of in-house designed machinery. “We call it a satellite hoe,” said Leonard

Graham, General Superintendent. “The principle is that the bulk of the machine stays on the surface and only the hoe, connected to the power source by umbilical cables and mounted on a concrete block goes down the hole.”

Using this equipment, the 22ft (6.7m) o.d. shaft was sunk at a rate of 10ft (3m)/two 8hr shifts/day.

Unlike Cementation’s shaft lining operation, Dillingham cast the in-situ concrete lining in 10ft (3m) sections as the shaft went down. In this way, a safe atmosphere was provided for the miners from falling ground thaw and security was also provided should an unplanned event occur, which history shows is possible.

But like the Cementation job, waterproofing between the concrete pours was not specified. About 200gal/min (757litre/min) of water seeped through the joints when freezing was suspended and subsequent patching and pointing was required. Drill+blast using a 2-boom Atlas Copco PR55 pneumatic drilling rig excavated the lower 100ft (30m) through the limestone to the tunnel horizon.

During the site visit, both shafts were down and the launch chamber for the Robbins TBM required for the 21,292ft x 30ft diameter (6.5km x 9.15m) interceptor drive at some 300ft (90m deep) through dolomitic limestone was excavated and fitted with starter walls.

Once the TBM launched, Dillingham anticipated completing the contract in February 1988, four months earlier than scheduled. n

Launch-bay waits for the Robbins TBM as it takes shape at the pit bottom

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Outline of the jacked tunnels beneath the rail tracks that connect the roadways to the immersed tubes across the Fort Point Channel

Passage of the road lanes of Boston’s Big Dig project of the late 1990s to replace an elevated highway underground, had to pass also under the sets of tracks at the approach to the city’s South Station railway terminus. While other designs were considered, it was a large box jack, supported by ground freezing, that was the method selected.

CASE STUDY APRIL 1997:

Box jacking on a grand scale

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ne of the most important criteria for selecting box jacking to take the Big Dig project highway lanes under the South Station approach railway tracks was to promote and maintain a high degree of confidence among third party owners through the planning, design, construction phases and during the lifetime of the facility. The principle third parties in this case are the Massachusetts Bay Transportation Authority (MBTA) that owns the railway facilities, and AMTRAK that maintains the tracks outside South Station on which pass several hundred trains daily.

The jacking concept is applied in three separate sections, each jacked section carrying two traffic lanes with an emergency breakdown lane, and each with an internal clearance of about 7m high x 20m wide. Two of the tunnel jacks take the eastbound and westbound carriageways of the I-90 highway under the rail tracks and the third is a two-lane I-90 westbound off ramp.

The tunnel jacking application in Boston is one of the largest uses of the technique in the world and one of the first applications of the method in the USA. The three tunnel sections comprise eight separate precast concrete elements of between 20m to 50m long, 11.5m high, and up to 24m wide, with heavily reinforced concrete floors and roof decks of 2m thick and walls of 1.8m thick. The off-ramp tunnel is 51m long and comprises two precast jacked elements, while the two carriageway tunnels are 79m and 116m long and comprise three elements each. Each element for the crossings is cast in large slurry wall supported jacking pits, and is being jacked into position some 2.5m to 12m beneath the rail tracks. At all times the tracks remain in service.

In early 1997, the Slattery Skanska/Interbeton/J F White/

Perini Corp JV was awarded Contract C09A4 as the lowest of three bids at $398 million.

In the 15m to 18m deep casting and jacking pits a 6mm thick steel base plate provides the interface between the concrete of the base slab and the underside of the element to be moved. The back walls of the pits are designed to withstand thrust forces of 11,000-12,000 tonne needed to push each element forward and ultimate loads of 18,000-19,000 tonne.

Excavation of the pits gave the JV immediate experience of the geological conditions expected ahead of the tunnel jacking. Historical records and preliminary site investigation data predicted complex, mixed and unpredictable conditions with the rail tracks built on reclaimed land under which are buried the granite blocks of the original sea front retaining wall and other timber pile-supported structures.

Below the fill are continuous deposits of organic silt with fine sand and some peat overlaying with the groundwater level rising to within 3m and 1.8m of the surface.

A major concern during design by section designer Mott McDonald, was stabilization of these weak soils.

Excavation of the material ahead of the elements was not a problem, but controlling the loss of ground at the 278m2 tunnel faces was critical, not only to limit surface settlement under the tracks, but also to maintain line and level accuracy during jacking.

Initially, the baseline design anticipated soil stabilization using chemical grouting and dewatering in the fill materials, horizontal jet grouting in the organic deposits, and soil nailing in the marine clay. The JV, however, was concerned about the risks associated with these 17

methods and suggested ground freezing as a value engineering alternative.

“It took about a year to progress from impossible to approval,” said Peter van Dijk, Tunnel Manager for the JV, “but the advantages in the end were convincing.

Ground freezing provided a complete treatment of the soil mass prior to the start of tunnel excavation, it lowered significantly the risk of ground losses through windows in the original treatment methods, and it improved stability measures by encapsulating large obstructions until cut up and removed. Freezing was therefore approved, and permission was granted by the railway authorities to gain access to the track areas for installation of freeze-pipes and brine-circulation systems well ahead of excavation activity.”

Specialist sub-consultant Mueser Rutledge of New York designed the freeze program, and ground freezing subcontractor Freezewall was engaged to undertake the installation. More than 1,700 freeze pipes were installed vertically and between the rail tracks. Calcium chloride (brine) at -30°C maintained the freeze. Being so close to Boston Harbor and the Fort Point Channel, the ground water is salty and -1°C is its freeze temperature.

Once established, the frozen ground was at about -10°C and had an in-situ ground strength of about 5N/mm2 to 10N/mm2, about the same strength as lean concrete. It took three to four months to establish the freeze and will take about six months to thaw completely once the freeze is discontinued.

Fig 1. Internal setup and principle of the tunnel jacking system

Excavation of the three jacking pits from which the three highway jack

The freeze pipes are installed on a 2m to 2.5m grid, and the frozen zones extend to about 2m beyond the side walls of the tunnel elements, to about 1m below ground surface, and about a meter above the base of the elements (Fig 6). “We left it above the tunnel invert because we didn’t want to alter the properties of the clay,” explained van Dijk. “Freezing followed by a thaw would induce clay degradation, and the clay in its natural state is a favourable foundation for the heavy tunnel elements once pushed into place.”

Expansion of these particular ground conditions when frozen is about 120mm on all sides, or about 1% to 2% by volume.

Beneath the rail tracks a maximum heave of 175mm was specified.

“During the planning and design stage, many of the concerns put forward by the track owners and service operators (MBTA and AMTRAK) hinged on how the freeze has to be installed, what are the consequences of a freeze operation, and the presentation of an acceptable contingency plan, should one be needed to slow down the freeze,” explained Phil Rice, Resident Engineer on the contract for Bechtel/Parsons Brinckerhoff. “Together with

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Jacking program

Within the JV, a considerable degree of experience and technical know-how was contributed by Edmund Nuttall of the UK that had completed five tunnel jacking projects in the UK working in close co-operation with John Ropkins, a consulting engineer in the UK. This is believed to be the first tunnel jacking operation to include ground freezing for stabilization.

k boxes under the rail tracks will be cast and jacked

MBTA and AMTRAK engineers and managers, in what has become a successful partnering relationship, these concerns were thoroughly investigated and managed to the acceptance of both the highway and the railway authorities.”

“In fact,” Rice continued, “it is noted that jet grouting used on other parts of the Big Dig project can cause heave much rapidly than freezing. Heave caused by grout injection can be 50mm in minutes, and there is little control on where the grout will go. With freezing, the change in level is about 2-3mm/day and the area of influence is well defined. There are a total of 1,200 survey points in the project area, including across the railway tracks. About 300 of these are read daily and the data is analysed by computer, held in the overall project database, and printed out as readily appreciated information. Crews of experienced railway maintenance workers are on 24h duty to undertake any necessary tamping of the ballast to correct rail tolerances.”

A major contribution to the project was the innovative anti-drag system (ADS) developed and patented by Ropkins. The concept is based on creating a carpet of closely spaced, 19mm diameter steel cables across the top and bottom of the boxes to create a stationary separation layer between the moving box and the overlying and underlying ground. These cables, about 1,000 across the top and another 1,000 across the bottom, are anchored using crimped-on copper sleeves to plates attached to the thrust pit headwall bracing beams, and are paid out from inside the element as the tunnel is jacked forward. The free end lengths of the cables are stored on the inside of the tunnel elements, on spools for the bottom cables and in brackets in the ceiling for the top sets. It is via slots cast into the leading edges of the shield at the front of each tunnel box that the cables are freely paid out as the boxes move forward. Grease is fed continuously to the cables through lubrication ducts cast into the concrete, to prevent snagging and further reduce drag.

Enough steel cable to see the tunnel boxes to their final positions is needed in the cable reserves at the start of each jacking operation. A total of more than 400km, or 1.5 million feet, of steel cable is needed to complete the three tunnel lengths. Once the tunnels are in position, the steel cable will be left in place. It would be a difficult, timeconsuming and uneconomical operation to retrieve the buried cables.

As well as preventing drag, the carpet of cables on the underside of the elements prevents the ground being compacted and produces the effect of tracks on which the box can slide. The cables across the top deck are designed in addition to transfer friction forces between the concrete roof surface and the greased cables to the cable anchors. The exact load on these upper cables is difficult to predict, but based on past experience and a conservative calculation, the load was estimated to be a

Row of rams across the invert of each pit for jacking the cast concrete boxes in under the rail tracks

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From left: Obstacles and decommissioned freeze pipes were cut out as they were uncovered by the Webster Schaeff roadheaders used to excavate the frozen face in 12 cells in the shield of the leading element; A Brokk jack hammer breaks out harder obstacles, top ADS cables disappear through slots to the outside of the moving element

maximum of 1.7 tonne/cable for the shorter ramp tunnel and 2.7 and 3.4 tonne/cable for the two longer I-90 carriageway tunnels.

Excavation sequence

To excavate the 278m2 face of the tunnels, the leading element of each is preceded by a 3.3m long concrete shield which is fitted with a steel cutting edge and is divided into 12 excavation cells by vertical walls and a temporary mezzanine working deck.

The frozen ground is excavated for the most part by four high-powered purpose-designed Webster Schaeff roadheaders from the UK, two working on the invert and two on the mezzanine. A Brokk hydraulic jack hammer unit is available on both levels to break up granite boulders and harder obstacles. Excavated material falls from the mezzanine to the invert, where a Gradall excavator and a CAT 906 loader gather excavated material into a central muck pile. From here a 42yd3 Wagner scoop tram transfers muck to a 4m3 skip at the back of the thrust pit which, when full, is lifted by crane for discharge on the surface (Fig 1).

includes a man lift on each deck and a 15 tonne cherry picker on the lower deck. With the machinery we have 28 miners, operators and electricians in each tunneling shift and work progresses on a two 10hr shift/day, 6 day/ week schedule. Progress is based on completing one 3ft cycle/day, excavating a 3ft round out ahead of the face first, and then jacking the box forward before starting the next excavation sequence at the beginning of the next day.” As excavation advances, individual circuits in the freezing regime are decommissioned, and the vertical freeze pipes are cut out using thermic lances as they are encountered.

Jacking forces to push the tunnel boxes forward are applied only at the invert, with a main jacking station at the rear in the jacking pit, and an intermediate jacking station between the elements in each two- or threeelement string. The jacks used on the job have the same capacity of 485 tonne each at 42 MPa working pressure and 808 tonne each at the maximum allowable 70 MPa pressure. The thrust cylinders are 520mm diameter and have a maximum stroke of 1,067mm for the 25 jacks in the rear jacking station. The 28 to 32 jacks in the intermediate jacking stations have a 419mm stroke. All the jacks are grouped together by manifolds in clusters of two or four “It is a machinery intensive operation,” said Steve Leius, with one set of hydraulic hoses from the hydraulic pump Tunnel Superintendent for the JV, “and the fleet also to each cluster. Jacking forces of up to 15,000 tonne total are Fig 2. Ground freezing used to stabilise water-bearing material and support transmitted from the base slab excavation of the 278m2 face of each box jack into the post-tensioned slurry walls of each pit.

Each jacking station is activated in sequence, caterpillar style, pushing each element forward at a barely perceivable rate of about 30min/900mm stroke. After each 900mm stroke, spacers are inserted at the rear jacking station and are replaced with 3,600mm permanent spaces as the jacking progresses.

The maximum 12,000 tonne pushing force available in the 25 jacks in the rear jacking station is sufficient to push the two or three-element strings for about the first 50m without

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engaging the intermediate jacks. This helps maintain alignment, as do the guidewalls. The elements are cast within 1.2m high guidewalls cast into the jacking pits with foam filling in the very tight tolerance gap of only about 25mm between the wall and the moving box. Friction on the side-walls can be reduced using a polymer gel lubricant. Heating elements cast into the concrete walls prevent the gel freezing when in contact with the frozen ground. Jacking is a delicate balance of keeping the ground frozen and the lubricant liquid.

Progress

Having started in mid-October 1999, the ramp tunnel jacking was completed in December 1999. At the end of the process, survey measurements indicated that the leading edge of the two elements of the tunnel came to rest within 80mm of their nominal vertical alignment, and within 60mm from their nominal horizontal location, well within the ±150mm tolerance specified. Tests of the antidrag system cables in the roof revealed that at the end of the 41m push, maximum load on a single cable was 1 tonne, or 60% of the design value.

By May 2001, all three jacked tunnels under the rail tracks were through. From the open cut thrust pits, the precast elements in each sting terminated in a section of cut-and-cover work. These excavations were stabilized by the soil-mixing technique with a skin of shotcrete covering the termination face. The only exception was for the last and longest jacked tunnel, where obstructions to soil mixing at the face caused a change of plan. Instead, a frozen ground mass had to be established to support the 20m deep termination

face as well as part of the cut-and-cover excavation.

Cut-and-cover excavation was then staged to remove the unfrozen ground ahead of the tunnel. Cantilever sheeting was installed to retain the unfrozen ground so that the frozen ground of the mining face would remain stable until hole through. After the frozen face was removed, a 26m span of frozen ground remained in place above the tunnel as the jacking shield of the precast tunnel box was pushed the last 3m.

Polyurethane foam to about 100mm thick was sprayed on to the outer surfaces as an insulation layer for the frozen ground and reflective plastic sheeting helped minimize solar gain. After the final push, concrete was placed to provide positive support of the ground above the jacked box. The cut-and-cover tunnel sections connect the two jacked carriageway tunnels with the immersed tube highway tunnels across Fort Point Channel and the third jacked off-ramp tunnel links an open cut transition to the surface.

During the site visit it was agreed that the tunnel jacking alternative is an expensive option but that in urban areas; under very shallow cover; beneath vital infrastructure which must be kept in operation throughout the construction period; and through soft, non-homogeneous ground conditions where dewatering is unacceptable and settlement a major concern; the method, in association with ground freezing for soil stabilization, is the best method.

Operation of the rail tracks above had continued undisrupted throughout. n

Polyurethane foam and reflective plastic over the frozen faces minimized solar gain and insulated the frozen breakthrough end wall of the last and longest jacked tunnel box with a thin pillar of frozen ground supporting a 26m wide beam of frozen ground above the jacked box for the last 3m push

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CASE STUDY JUNE 1992: With shallow underpasses needed beneath rail and highway infrastructure on the surface, microtunneling found application for very special purposes, one of them to install with accuracy the bores needed to install a ground freezing regime.

Micro assistance for macro underpass projects

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n Mannheim, Germany, the twin tube Fahrlach road tunnel passes directly beneath the 10-track railway approach to the city’s main train station.

Intermittent beds of gravel, sand and silt. Groundwater 3.5 to 7.5 m below the land surface. The tunnel is largely located in water and over a length of 184 m is beneath railway tracks. On no account were train services to be disrupted, In two separate phases, an AVN 300 microtunnelling system was used to install horizontal ground freezing pipes required for safe excavation of the two 100m2 x 186m long roadway headings.

The microtunnelling system completed 46 drives of 90m long x 454mm i.d.

(470mm o.d.) from each portal to cover the full length of the motorway underpass (Fig 1).

From left: Fig 1. The AVN micro system successfully installed the horizontal freeze pipes prior to excavation of the twin tube Fahrlach road tunnel just 2.6m beneath the main railway lines in Mannheim; Each 470mm o.d. micro bore was launched through a rubber seal in the sheet piled end wall of the large tunnel portal

A total area of 27,000m² had to be frozen which, at the time, was the largest project of its kind in the world. A further special feature was excavation of a smaller diameter auxiliary tunnel beneath the railway tracks to feed water into the crown area for freezing the crown zone of the road tunnels, which was above the groundwater table, and for creating the middle partition wall and installing equipment for monitoring the temperature and security of the freeze zone.

At the end of each 90m drive, the micro machine had to penetrate 1m into a pre-installed vertical freeze wall at the half way point and be withdrawn to avoid becoming frozen into the drive. An innovative sacrificial cutting wheel allowed the machine to be retracted through the

finished pipeline. The AVN machine worked through water-bearing sands, silts, gravel and fill material that included old tree stumps.

The five-partner consortium, led by Bilfinger + Berger and Hochtief, completed each 90m long bore in two 24h working days on average with an accuracy within ±4cm on line and ± 2cm on level and level.

Atlanta metro underpass

In Atlanta, USA, an AVN 600 microtunnelling system was used to accurately install horizontal interlocking pipes to create a pre-supporting arch prior to excavation of two metro tunnels directly beneath the busy eight-lane I-285 highway around Atlanta.

The AVN rock cutting wheel emerges after successfully completing another micro bore for the presupporting arch

SEC, the specialist micro-tunnelling contractor to main contractor ArcherWestern, installed the 42 x 55m long x 770mm diameter pipes (a total of 2,305m) in six months. Best advance was installation of one 55m long bore in 1.5 days working two 10hr shifts/day.

The AVN slurry system was equipped with a rock cutting wheel to successfully excavate residual soils and weathered gneiss as well as cut through an old concrete filled storm sewer and several large boulders.

Calling on other technologies in the industry to support tricky excavation projects is part of the processes for making the underground option viable and cost effective. n

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CASE STUDY SEPTEMBER 2003: As far as possible, public infrastructure tunnels in the USA avoid passing under private property. It is expensive to gain the necessary permits to do so and once obtained, it is expensive to manage the works to the satisfaction of third-party property owners. There are situations however, where passing under private property is simply unavoidable. One such case was in Boston where the Silverline transit route passes directly beneath a 100-year-old historic office building. To achieve this the industry was called upon to use techniques of design and construction not used before in the USA to protect the buildings above and ensure safe and secure excavation.

Shani Wallis of TunnelTalk visited the job site in 2003 to report on the process.

Ground freezing supports NATM under historic Boston buildings

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lanning of the Silverline transit system for Boston by the Massachusetts Bay Transportation Authority (MBTA) started in the mid-1980s and was realized in three phases. Phase 2 of the new line required the widest range of underground construction techniques to complete. The first 3km (1.8 miles) of the 3.5km (2.2 mile) section from Boston’s South Station railway terminus is built as part of the concurrent Central Artery Big Dig highway project with the two-lane transitway built into the top of the concrete boxes of the cut-and-cover Big Dig highway lanes. The alignment then veers off to pass 427m (1,400ft) directly beneath the buildings of the 100-year old Russia Wharf complex which connects to an immersed tube across Fort Point Channel.

From a cut-and-cover section on a demolished building site behind the Russia Wharf complex, the underground transit line runs on a steep 3.5% incline to the alignment on top of the Central Artery cut-and-cover box for

passage into its cut-and-cover passenger lobby at South Station. Under the historic seven-story high, brick and steel frame Russia Wharf office buildings, the alignment runs on a diagonal entering at the southwest corner at the Congress St/Atlantic Ave intersection and passing just 18m (60ft) to its invert beneath the basement parking garage level and a limited 3m (9ft) above the tunnel crown to the surface of the vital traffic intersection outside South Station. Although only short, at about 120m, this underpass would be highly sensitive with the city’s landmark Federal Reserve skyscraper on one corner of the intersection above and with the owners of the Russia Wharf complex requiring that the offices remain occupied and operating at all times during construction. Another complication was that several of the old wooden foundation piles of the Russia Wharf building are in the way of the transit alignment and will have to be cut out and removed as part of the excavation work.

The geology of this waterfront area of Boston is best described as saturated soft ground, comprising manmade fill and organics overlaying Boston Blue Clay. During preliminary design various options were investigated, including cut-and-cover, shield tunneling with liner plates, elliptical pipe arch pre-support with liner plates, and a rectangular box jack. All were unable to compete technically and economically with the alternative of using a NATM solution introduced by DSC, the Dr G Sauer Corporation of Herndon, Virginia, as subconsultant to the client’s section designer DMJM+Harris. Limiting settlement, controlling excavation, and protecting the buildings would be the key to success.

Open cut section behind the Russia Wharf complex (left) from which the NATM tunnel progresses beneath the two seven-story buildings (Fig 1 below)

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make way for the basement garage of the high-rise hotel to be built on the vacant lot that is being used as the contract work site.

Ground freezing and mini-pile supports equipped with compensation jacks installed in the basement space of the Russia building providing pre-supporting ahead of tunnel excavation

To further control excavation of the 12m wide x 8.2m high (38ft x 27ft) binocular two-lane tunnel, mini piles will be installed to support the main building and ground freezing was selected to stabilize the soft saturated materials of the upper part of the excavation profile. This is believed to be the first use of NATM in combination with ground freezing support in the USA. “Ground freezing was used as the most prudent and time- and cost-effective method for supporting excavation under the three historic buildings of the Russia Wharf complex,” said Ed Karpinski, Deputy Director of Design and Construction Silverline Phase II for MBTA. “Cheaper methods were considered, including taking out the lower two floors of the seven-story Russia building and working a cut-andcover operation in the space but that was unacceptable to the building owners who wanted to keep the buildings fully tenanted and operating throughout the works.”

Once these decisions were confirmed by MBTA, DSC was retained to design the 122m (400ft) long NATM tunnel under the complex; Mueser Rutledge of New York to design the ground freezing stabilization and mini pile underpinning supports and GEI Consultants of Winchester joined the team as the geotechnical engineer. During construction DMJM+Harris and DSC would be retained to provide supervision, monitoring interpretation, and technical advice services.

In mid-1999, the $96.7 million construction contract was awarded to Modem Continental in a joint venture with BeMo, the USA division of Austrian contractor Beton-und-Monierbau, to supply a team of site engineers and experienced foremen to manage a closely controlled NATM excavation. Layne Christensen was subcontracted to install the minipiles and Fig 2. Section of the binocular shaped Silverline tunnel beneath Russia Wharf establish and maintain the associated ground freezing system. To further maintain full control of the excavation, the first outbound The first decision to achieve this was to select a binocular tube of the binocular profile will be completed first and its shape for the two transit tubes. “This design was adopted waterproofing membrane and final lining and the center for several reasons,” said Gerald Skalla, Senior Engineer wall installed before excavation of the second inbound with DSC. “The profile of one larger single tube twin tube begins. track tunnel would have a higher crown arch but under the building and the limited cover of the alignment, there was no room for a high crown. This binocular design All reparatory work to install the mini underpinning piles provides the two vehicular operating envelopes in the and establish the ground freezing of the upper saturated most efficient excavated area and the central concrete soils had to be undertaken within the confines of the wall with refuge niches at regular intervals, provides a basement garage space of the buildings using low profile safety barrier between the operating lines.” The binocular pile and drilling equipment. When contacted in middesign was chosen also due to the close proximity of April 2001, Steve DelGrosso, Senior Project Manager for the building’s foundation pile caps to the tunnel crown Modern Continental, reported: “Installation of minipiles is beneath a minimum overburden of less than 3.6m (12ft), progressing and freezing of the ground for water cutoff at and with its ability to meet the very tight deformation limits the Russia Wharf site has started. Once these permanent to protect the historic brick building. At the start of the and temporary underpinning works are complete we can drive, the tunnel crown is further lowered and flattened to start NATM excavation.”

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From left: NATM excavation with ground freezing pre-support in the crown, removed a forest of old timber piles and transferred the load directly onto the tunnel structure performing as a strip foundation; Cut through timber piles were fitted with a pile shoe designed to transfer load onto the tunnel structure yet allow movement between the two

To create the freeze zone, more than 3,200m (10,500ft) of vertical pipes and two refrigeration units circulated -30°C (-22°F) brine to freeze the saturated soils and maintain a 2-6m (6-20ft) thick arch of frozen ground above the NATM excavation and to about spring line in the tunnel face. When temperatures reached the specified -15°C, NATM excavation began. With the freeze-support solidly established, the brine circulating refrigeration plant is operated only to maintain the freeze. “The plant operates about 7 days on and 20 days off,” explained Skalla. “We don’t want the freeze to grow or migrate any further than is necessary. Freeze-induced heave can be as damaging as excavation settlement. The freeze extends further into the tunnel face than we might have designed, but caution was the prerequisite and the freeze certainly provided the confidence levels needed to progress the works.” The freeze will be maintained through excavation of the second tube and only suspended when all is fully complete. It will then be force thawed to return the ground to its natural condition in about nine-ten months, or about half the time it would take naturally.

For the 350 or more historic wooden piles that had to be cut off out of the freeze-support excavation, each was fitted with a specially designed pile shoe encasement for being incorporated into the lining of the tunnel. Some of the mini piles are incorporated into the center wall of the binocular tunnel structure to further support the old building as part of a permanent underpinning system. Once the ground thaws, the cut-off wooden piles will rest directly on the tunnel’s lining, transferring their load to the tunnel which will act as a strip foundation to support the building permanently.

The pile shoes also incorporated neoprene pads to allow sufficient separation for independent movement of the piles and the tunnel and eliminate the transfer of vibrations from transit operations into the office buildings.

As well as being the first use of freeze-supported NATM excavation in the USA and North America, several other innovations and value engineered cost- and time-saving proposals have been implemented. One of the most significant, suggested by BeMo and supported and approved by DSC well after excavation had started, was to substitute the design’s reinforced in-situ concrete final lining with a final steel fiber reinforced shotcrete lining. Instead of #4 rebar erected at 150mm (6in) centers longitudinally and radially, a final 300mm (12in) thick layer of 40kg/m3 of Bekaert ZP 305 steel fiber reinforced shotcrete will provide the same structural properties required by the original in-situ concrete design. A layer of welded wire mesh, a lattice girder on 0.75 to 1m centers, and a second layer of

mesh, provides a frame on which the steel fiber shotcrete will be applied. With a lining of about 650mm thick, this is about the same final support structure as the original reinforced in-situ concrete lining design. Once the final lining is installed, the surface will be finished with a 50mm (2in) thick smoothing layer of fine aggregate, plastic fiber reinforced shotcrete. The polyfiber will mitigate shrinkage cracks and contribute to fire and life safety features in the public use tunnel, explained Leslie Becker, MBTA’s Project Manager for the contract.

When TunnelTalk visited the site in mid-2003, crews had completed excavation of the first tube, had installed the PVC membrane, and were busy casting the reinforced in-situ concrete central wall with its special plinth at the top that connects the binocular tubes. Working inside the PVC waterproofing membrane, crews were taking care to avoid damaging the membrane as they installed the rebar reinforcement and carry out the necessary welding. Once the center wall is complete, the permanent steel fiber reinforced shotcrete lining will be applied using a semi-wet system that introduces water to the dry mix hose some 6m from the nozzle. “Wet shotcrete was considered but the volume of shotcrete needed for each tightly controlled NATM excavation round was too small for the wet mix batching or delivery setup,” said Norbert Fuegenschuh, BeMo’s senior tunnel engineer on site. “The steel fiber reinforced final lining alternative to rebar reinforced cast concrete for the tunnel arches will save about two months on the 18-month NATM tunnel construction period and about $300,000 in costs. It avoids the building of complex one-off sets of formwork and will be much faster to apply.

Steel fiber also avoids damaging the PVC membrane during rebar reinforcement installation.”

When excavation started, the first 52m2 (560ft2) tube plus the center wall zone was progressed using a Liebherr tunnel excavator and divided into a 32m2 top heading followed by a subsequent 20m2 bench. Each 0.75m to 1m (2.5m to 3.5ft) advance of the top heading was sealed immediately with a 50mm (2in) flash coat of steel fiber reinforced shotcrete. The contractor’s shotcrete mix was said to be achieving high early strengths. “The design requires a strength of 2,500psi within 24 hours, 3,500psi in 7 days and 5,000psi in 28 days,” said Skalla.

“In fact, tests indicate strengths of 2,500psi well within 24 hours and the rapid rate of strength development has achieved 28 day strengths of up to 10,000psi.”

The PVC membrane waterproofing system is of a closed design. It is installed in isolated sections to allow for 25

From left: Piles on the center line are incorporated into the cast concrete centre wall of the binocular tunnel; Top heading excavation through the upper frozen ground is followed by a bench/invert excavation and closure of the immediate support shotcrete ring

remedial grouting if necessary to ensure a completely dry tunnel structure.

A tour into the basement and around the other Russia Wharf buildings during the visit, revealed the degree of monitoring instrumentation installed. In addition to surface leveling points, strain gauges, inclinometers, extensometers, tilt meters, and crack monitors, there are also sensitive hydraulic jacks installed between the top of the support frame resting on mini piles and the underside of the building columns. These are adjusted to compensate for any excessive heave or settlement encountered.

As part of the excavation responsibility, a comprehensive data monitoring and evaluation model was developed under which all data from building, surface, freezing and in-tunnel monitoring instruments are combined and overlayed with the construction progress and presented Waterproofing installed ahead of final shotcrete lining

graphically. This allows immediate access to all available data for a specific area, should deformation thresholds be exceeded. To date results confirm that all deformations are within the specified limits.

Convergence points within the first tunnel tube excavated recorded a maximum settlement in the crown of 10-15mm and a maximum sidewall convergence of 40mm, said Skalla. “The side wall convergence is somewhat outside the design specifications, but the vertical deformation taken from the roof leveling point, was still always inside the threshold values and the surface monitoring still did not show any movements due to NATM excavation.”

There are some cracks in the old brick buildings but this particular corner of Boston has been subjected to extensive ground excavation operations over the decades, including most recently the deep open-cut excavation of the Central Artery tunnels and a deep ventilation structure for it directly adjacent to the Silverline open cut and NATM work at the back of the Russia Wharf complex. Freezing is said to have contributed some to the cracks but the compensation jacks in the mini-pile foundations have limited the impact of the surface movement to the very minimum. They will be required to do the same during the thaw of the freeze support. The surface monitoring program is said to have barely noticed the NATM excavation work to date.

“Since work started, we have achieved the undertaking not to disturb the normal routine of the office buildings,” said Karpinski. “A comprehensive plan is in place for possible evacuation of the buildings but no emergency of any kind has occurred and operation of the offices has carried on above the construction activity as usual.”

Given the work going on in the basement and under it, about 1,250 people who work in the office buildings came and went each day without concern for the efforts of the tunnelers just inches beneath their feet. n

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CASE STUDY JUNE 2009

New York calls on freeze to aid East Side Access advance

O

ne of the shortest but most challenging sections of the East Side Access railway project in New York to connect the Long Island Railroad in Queens to Grand Central Station in Manhattan, was route underpass directly underneath Northern Boulevard in Queens. The proximity of existing infrastructure presented a host of ground and structural support challenges on the US$96.8 million CQ039 contract awarded to the Schiavone-Kiewit joint venture in 2008 to excavate this vital 120ft long (36m) segment of rail tunnel.

Excavation of the all-underground route is progressed from two working access pits, one for the soft ground TBM tunnels east to the Sunneyside LIRR connections and the other for the rock TBM tunnels into Grand Central Station (Figs 2 and 3). In between is the 150ft (45m) wide Northern Boulevard corridor (Fig 4).

Northern Boulevard is a busy six-lane truck route leading to the Queensboro Bridge, and includes a four-track cutand-cover subway trunk line underneath the roadway that carries the E, M and R subway trains and the elevated N and Q subway trains overhead. Without exception, traffic and subway services along Northern Boulevard must remain in operation throughout the construction works.

The underpass is designed as a three-track sequentially mined excavation of 150ft long x 40ft high x 56ft wide (45m x 12m x 17m) at about 60ft (18m) below the surface at invert level and with about 8-10ft (2.5-3m) of ground cover between the crown of the underpass and the underside of the operating cut-and-cover subway above (Fig 3). The elevated transit line is about 30ft (9m) above the surface and is built on columns about 35ft tall which are grouped in pairs and supported on clusters of 16in (32mm) pipe piles of about 20ft (7m) deep.

While dewatering was allowed to support excavation of the ‘bath tub’ design open cut working pits, no dewatering was permitted under the Northern Boulevard structures.

As the alternative, ground freezing was adopted to support the soft waterbearing soils during excavation and cut-through of the elevated subway support piles, the elevated structure supported on a temporary system of underpinning.

Above: SEM with ground freezing support beneath Northern Boulevard; Below: Video: Explanation of the freeze process

by Paul Schmall, then of Moretrench, now part of Keller

The Dr Sauer Corporation (DSC) was section designer of the sequential excavation, ground support and final lining elements of the underpass and Moretrench, now part of the Keller Group, designed, monitored and maintained the ground freezing installation.

During a site visit to the project in 2009, TunnelTalk recorded a video of the contract progress where excavation was complete, the final lining waterproofing membrane was being installed and the ground freezing system was about to be decommissioned after successful excavation of the tunneled underpass. n

Fig 1. East Side Access alignment; Two working access pits for the soft ground TBM tunnels to Sunneyside LIRR connections and the other to the rock TBM tunnels into Grand Central Station are divided by the Northern Boulevard underpass; The bearing loads of the cut-through support piles of the elevated subway structure are transferred onto the tunnel structure

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CASE STUDY AUGUST 2017

Collapse of freeze assisted TBM drive at Rastatt

C

ollapse of a TBM drive through ground freezing pre-support under the main railway line at Rastatt in Germany in 2017 halted all rail traffic between Karlsruhe and Basel, Switzerland, and demanded backfilling of the new tunnel with concrete, burying the TBM in the process.

The 4,270m long twin tube rail tunnel is part of a 17km long project to double the capacity on the Rhine Valley rail corridor from two to four tracks, taking an underground route beneath the city of Rastatt. To limit the length of underground construction and maintain acceptable gradients for the 250km/hr rail lines, the TBM drives are aligned up to 19m maximum in depth with the 10.97m diameter TBMs passing a minimal 4m beneath the mainline surface rail tracks. To support the shallow alignment through loose sand and gravel deposits, a collar of horizontal ground freezing was installed. Subsidence under the surface tracks detected by monitoring instrumentation progressed rapidly to create a depression of 500mm, buckling the rails and suspending all traffic on the line.

At the time, the TBM in the leading east tunnel bore was about 40m beyond the rail underpass and just short of breakthrough into the reception shaft, which was also access for installation of the horizontal ground freezing operation. The trailing TBM in the west tunnel was about 1,000m behind at 3,064m into its 4,250m drive.

Immediate response to the incident was to install three slick-line holes into the new tunnel to create a concrete plug about 150m behind the cutterhead and fill the new 9.5m i.d. segmentally lined tunnel with 10,500m3 of concrete (Fig 1).

According to a press briefing by Section Manager Jürgen Kölmel for project owner Deutschebahn, the segmental lining of the tunnel under the rail tracks and 40m behind the TBM did not crack or collapse but rather the seven segments in the 500mm thick x 2m long rings dislodged creating gaps and allowing infiltration of water and ground. This indicated a failure of the freezing regime and possible over-excavation of material as the TBM passed through the zone. Up to 370 trains/day were diverted away from the closed section of surface rail route.

Work on the €693 million contract to complete the twin TBM drives was awarded to the Ed Züblin/Hochtief JV. Two slurry Mixshields from Herrenknecht were procured and launched from the north transition portal in May 2016 and September 2016. Due to the shallow alignment of about 5m at the start of the drives, a section of angled ground freezing from the surface created a canopy over each TBM tube to protect against potential slurry blowouts for a distance of up to 290m.

According to technical reports, extending operation of the TBMs under the main railway lines was a contractor 28

proposed alternative to the project design to use openface NATM excavation through the ground freezing support. The alternative was said to result in construction savings and was approved after comprehensive study.

The 200m long horizontal freeze for the rail underpass was established from two 30m deep shafts installed about 100m either side of the tracks. From the shafts a circle of 42 x 100m long freeze pipe holes were drilled using horizontal directional drilling and the freeze applied created a 2m thick collar of frozen ground around each 10.97m o.d. tunnel tube.

The exact cause of the tunnel failure was the subject of intense and wide-ranging investigation to include freeze management, instrumentation and monitoring reviews, TBM operation, and operator logs. Reports in the local German media speculated that the integrity of the ground freezing operation was undermined by a recent period of high summer temperatures combined with periods of heavy rainfall.

Industry discussion

Although thankfully rare, and given all the hundreds and thousands of successes, it is the incidences of tunnel excavation failure that shape the industry for the future.

Pushing the boundaries is a must for taking the industry forward but managing the risks and learning from the causes and consequences of any failure is equally as important.

The failure of the Rastatt TBM rail tunnel in Germany prompted a series of communications from the industry, representing the various aspects of the event. These included the following comments and concerns, all of which are under official investigation: • Why was the alignment under the railway so shallow?

On a TBM tunnel of 4.3km could not the underpass on its oblique alignment under the rail tracks have been deeper (Fig 2). The reported 4m of cover under a rail embankment structure is less than half the rule-ofthumb of a minimum of one tunnel diameter of cover above TBM drives.

• Can ground freezing and a slurry TBM excavation be compatible? Managing the balance between keeping the excavation support and muck haulage slurry fluid and ensuring a frozen ground support will have been difficult to specify as well as maintain, for both the incoming fresh slurry and the out going loaded slurry, as well as for the slurry mixing operation in the excavation chamber.

Study of reported figures state that the freeze pipes were installed from two shafts located 100m either side of the railway and drilled horizontally for a 100m from each shaft.

That being the case, the ends of the two freeze pipe installations are at the mid-point of the total 200m length, which will have been directly under the rail tracks.

If that is the case, what was the junction or overlap of the freeze installations at this critical mid-point? It would have been difficult to check deviation of the pipes after 100m of HDD drilling and confirming the freeze from the surface at that point would have been prohibited by the surface trackway.

Breaches in freeze installations drilled from the surface for shaft excavations are well known.

Additional queries that arise include: • Why did the segmental lining open up? Where was the annular backfill? Maybe it too was adversely affected by the ground freezing environment. Were the Freeze assisted TBM drive collapse at Rastatt, Germany bolts securing the lining still in place or already removed as is becoming common practice?

What was the configuration of the bolted lining? Were bolts across both the longitudinal as well as circumferential joints?

• What part has monitoring played?

Accurate monitoring of a freeze operation would/should have indicated a potential freeze failure.

• Can a freeze operation so close beneath a vital set of high trafficked train tracks be a sound option when a secure freeze is as vital as avoiding ground heave under the tracks? What was the effect of Fig 1. Schematic of the TBM drive collapse and recovery the vibration from the heavy and similar problems on the rest of the drive. However, regular trains on both the freeze and the integrity of the consequences of each of the failures have been the segmental lining and TBM operation under such a catastrophic. shallow cover?

• What was the method of contract procurement, the risk allocation regime within the contract, and the approval To date, the best documented of the failures is that at process for accepting the TBM alternative over the Hull, which was the subject of an investigation that was original freeze supported open-face operation under summarised in a report by Grose and Benton [2005](1). the tracks.

Even in this case the investigation was limited and the • Was rectangular boxjacking through the freeze conclusions tentative. support as used under the South Station railtracks in Boston in the late 1990s (see p17) considered for the The paper was the subject of a number of discussions, shallow Rastatt main railway line underpass? to which I contributed, and which elicited detailed responses that contained much additional information to Readers of TunnelTalk also contributed additional that in the original paper(2). In my opinion, the conclusions thoughts and concerns: were inconsistent with some of the observations made in the tunnel; I stated this in a further discussion, which was Nick Shirlaw offered the following feedback: “As far as submitted, but rejected by the journal on the basis that I am aware, this is the fourth incidence of catastrophic they did not accept a second round of discussions. segmental lining failure behind a pressurised TBM in the last 18 years; these being: The failures at Cairo and Okayama have been the • Hull wastewater transfer tunnel, UK [1999](1,2) subject of a number of articles in TunnelTalk, but I have • Cairo Metro tunnel heading, Egypt [2009](3) not seen any definitive explanation of causation. It is rare • Okayama pipeline tunnel, Japan [2012](4) to get good forensic information at a later date but how • Rastatt railway tunnel, Germany [2017](5) can realistic risk assessments be carried out if there is a fundamental lack of information on the frequency or I know of two other cases of severe, local, distortion cause of ground loss incidences? Because the failure of of gasketted, concrete segmental tunnel linings, in segmental linings is so rare, those listed above have each Singapore and the USA, where total failure was avoided occurred in different countries. As far as I am aware each by providing additional support in the tunnel. has been assessed in isolation. I hope that the detailed results of the investigation into the failure at Rastatt are Given the huge number of segmentally lined tunnels built made public, but this will take months or years, based on over the last 18 years, the proportion that have failed is previous experience. Given that there have been several tiny; and in each case the failure has been local, without failures there does appear to be a case for reviewing 29

Fig 2. Construction elements of the tunnelled route under Rastatt

them together, to see if there are any common features, and lessons to be learned to reduced the likelihood of another incident.

Author’s References 1. Hull wastewater flow transfer tunnel: tunnel collapse and causation investigation, Grose and Benton, 158, October 2005, Issue GE4, Proceedings of the Institution of Civil Engineers, Geotechnical Engineering 2. Hull wastewater flow transfer tunnel: tunnel collapse and causation investigation, discussion report, Ground Engineering, Volume 159 Issue 2, April 2006, pp. 125-128 3. Cairo Metro tunnel collapse - TunnelTalk, Annual Review 2010 4. Salvage team recovers Japan disaster TBM - TunnelTalk, Annual Review 2013 5. Toronto EPBM recovery reveals the unexpected - TunnelTalk, Annual Review 2010 6. Shirlaw, J.N., Boone, S. (2005). The risk of very large settlements due to EPB tunnelling. 12th Australian Tunnelling Conference, Brisbane, April 2005

Rupert Sternath commented on the Rastatt collapse: “One can see out of the available publications that the segments of the lining have dislocated some 40m behind the Rastatt TBM. This is an indication that the ring gap has not been filled properly. As this happened to an experienced contractor it may be the case that the grouting operation together with the TBM drive through a frozen soil includes some particular problems.

collapses and refers to precast concrete segmental lining failures. But is it truly a “failure” in the usual sense of the word if the lining collapses under a load for which it was never designed nor intended?

Mining through an ice body has the characteristic of a hard rock drive, which requires some over excavation to enable shield steering.

What I am talking about here is running or flowing ground and I am reminded of the collapse in Hennessy Road during the Hong Kong Island Line construction on 1st January 1983. The hole in the rock face through which the CDG flowed under water pressure was no bigger than a fist when the flow started. But the flowing ground opened it up so much with abrading material that we ended up with a full size street lamp within the debris in the tunnel.

Most shielded TBMs use grout lines through the shield tail to fill the annual gap immediately behind the tail seal.

Under hard rock conditions the mortar tends - due to the over excavation - to flow around the body of the TBM and to the front and into the working chamber and so leaving voids outside the segmental lining. These voids have to be filled by a secondary grouting operation through the segments as soon as possible from the top of one of the trailing gantries.

In case of a frozen soil outside the gap however, it may happen that the voids are being filled by groundwater, which would also freeze, and as heat is present inside the tunnel during the mining process, the ice in the gap may melt leaving the segments unsupported. In this case filling of the gap by blowing pea gravel through the segments combined with a cement grouting operation may be a better option in my view.”

David Caiden questioned the appreciation of segmental linings. “In the discussion about the Rastatt collapse incident, mention has been made to some classic tunnel 30

Fig 3. Core samples

Consider this: A car gets flattened by a meteorite - would we say the body shell had “failed”? I doubt it. We would say it was “flattened by a meteorite.

My point is that flowing ground is an immensely destructive force similar to rushing floodwater. Segmental linings are designed for static ground forces in the permanent cases, and handling and building forces for the construction stages. They are not designed to withstand immense dynamic and changeable flowing ground forces with a battering of cobbles and other debris. The approach we take to overcome this disregarded loading case is to take measures to prevent ground flows. Naturally when these measures are unsuccessful the ring of lining segments will not hold up.”

Tim Hyett wrote in the TunnelTalk LinkedIn group: “The Rastatt article highlights the major risks of shallow cover tunnelling using pressure balance TBMs, not helped, no doubt, by the far too frequent trend of designers to focus on transverse loading of the ring only, and ignoring minor

longitudinal deformation of the tube lining behind the TBM, and the practice (originally imported from Europe) of removing/recycling segment bolts. Taking out tunnel segment bolts in anything other than the most stable of ground is something that would have been thought madness 20 years ago, yet seems common-place today.

The investigation into the tunnel collapse in Hull in the UK in 1999 wasn’t anywhere near conclusive, but ask any of the miners who were frantically trying to reinsert the bolts and they will tell you what would have prevented it.”

Auke Lubach commented: “Interesting problem to analyse. In addition, what is the possible effect of stray current from the railroad on ground freezing?”

Wasim Ashraf queried the cost of the freeze: “I would love to see the cost comparison between mix-in place and/or grouting vs the ground freeze technique used for the 200m length under the tracks in Rastatt given the soil strata shown in the image of the core samples in this article (Fig 3).”

Another reader considered the immediate response to backfill TBM tunnel drive failures with concrete and burying the TBM and its back-up in the process, suggesting that there must be a better method for stabilizing the failure zone, which in the Rastatt case was 40m behind the TBM shield bulkhead, although still over the backup gantries, and avoid the destruction of the TBM in the process.

A year after collapse

One year after the critical collapse, work on the new Rastatt high speed railway tunnel beneath the mainline surface railway was continuing towards a much delayed completion. When the leading east TBM drive collapsed in 2017, about 10,500m3 of concrete was pumped into the collapsed east tunnel and a massive concrete slab of 270m long x 1m thick, comprising about 3,000 tonne of concrete and 540 tonne of reinforcing steel, was built to restore the damaged surface tracks (Fig 4). Lines were installed to inject more concrete in the event of any subsequent subsidence.

On 2 October 2017, traffic on the Rhine Valley railway rolled again and, after 3,672m of its 4,030m drive, the trailing west tunnel TBM continued to reach the surface railway tracks in early December 2017, where it has been in a waiting position since. With investigations into the cause of the collapse still ongoing, excavation of the last 60m and 360m of the east and west TBM drives respectively remains on hold while construction work on other elements of the project continues.

As an immediate measure after the collapse, a concrete plug was inserted and about 160m was backfilled with concrete, through the backup, including a muck haulage train of muck skips and locos, and into the TBM shield to the collapsed tunnel face. At the beginning of February 2018, the first work began on dismantling the 2,000m3 concrete plug after the rails for the TBM supply trains from the north working access portal were dismantled and a temporary invert installed to host wheel-based excavators and haulage trucks. After dismantling the concrete plug, backfill concrete was also removed although no decision was yet made for uncovering the 93m long TBM.

Core drillings to help clarify cause of collapse

A shaft was then built onto the segmentally lined tunnel to serve as an escape route and to advance the nine cross passages in the completed lengths of the parallel tunnels from the north portal.

Since mid-May 2018, the Ed Züblin/Hochtief JV and project owner Deutsche Bahn (DB) have been conducting a drilling program to broaden the investigation of the geological conditions in the collapse zone. A total of about 60 boreholes of up to 25m deep were drilled over a length of about 300m of the rail tunnel route (Fig 3), nine of which will become piezometer for groundwater measurements. On the basis of the drilling results a concept for completing the new ground freezing TBM rail tunnels can be developed.

In the meantime, evidence to clarify the causes of the collapse was ongoing, as was the arbitration procedure agreed between DB and the construction JV for continuation of the collapse recovery. A report on the reasons for the collapse was not expected until into 2019, said a DB spokesman.

The consequences of the closure of the mainline railway for passenger and freight rail traffic totalled economic losses of more than €2 billion. As a direct result of this economic impact, DB conducted an internal disruption report. In addition, the European freight railway associations are collaborating to develop a handbook for optimum reaction in the event of an incident and to provide guidelines for uniform processes and better communications for crossborder railway operations. The German railway sector also planned guidelines for construction site management to improve processes associated with the country’s programme for modernising its rail network. n

Fig 4. Details of leading TBM drive collapse by Deutsche Bahn

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Fig 1. Installation of freeze pipes, dewatering pipes and temperature measurement pipes for the 2m wide freeze collar

Ground freezing assistance CASE STUDY OCTOBER 2018: Cross passages between the twin tubes of the new highway

under the Suez Canal at Ismailia in Egypt were excavated with the assistance of ground freezing. Authors Ibrahim Raafat, for the client EAAF; Haider Fadhel, for designer CDMSmith GmbH, Germany; and Mina Philips, of Arab Consulting Engineer; explained in an article for TunnelTalk how a freeze zone was established to support the sandy and silty soil below the groundwater table and under a hydrostatic head of up to 5 bar.

A

t 4.8km long and 11.4m i.d., the twin tube road tunnel under the Suez Canal at Ismalia was procured by the Egyptian Government and excavated using two 13m o.d. Herrenknecht Mixshields. The new highway passes under a main railway line, the old Suez Canal, and the new canal which opened in August 2015. As they progressed, the Mixshields erected 600mm thick x 2m wide rings of segmental lining.

While the design of the four cross passages required avoids locating any passages directly under the waterways, two are located close to the canals and required the extra support of ground freezing for their excavation. This is in addition to segments of heavier reinforcement were erected in the area of the cross passage breakouts and pre-grouting applied at cross passages to support breakout of the lining and to transfer stresses to the strengthened ground.

Drilling for the freeze pipes was executed according to designs prepared by CDM-Smith Consult, which considered the compliance with the geothermal design and potential deviation of the drill holes (Fig 2). Close monitoring considered whether additional drill holes were required. Dewatering stand-pipes fitted with blow-out preventers were installed and pressure tested to verify the water tightness of the connection. Dewatering pipes would also release ground water in the core, in case of increased water pressure.

Preparation for cross passage breakout and installation of the freeze pipes began once the TBMs passed the cross passage zones. Subject to structural design confirmation, a full circle watertight brine-freezing collar of about 2m thick was established around each cross passage excavation (Fig 1).

32

Up to 48 freeze pipes were installed to form the freeze collar. Temperature measurement pipes of 3m long were installed along with 6m long dewatering pipes. The closed circuit freeze system chillers were located inside the tunnel at about 40m from the cross passage breakouts and temperature measurement pipes were installed from the opposite tunnel.

Freezing technique principles

Ground freezing is based on heat withdrawal from the soil. A close-ended freeze-pipe is placed in the soil and an inner, or supply, pipe is inserted into the freeze pipe. The cooling medium flows through the supply pipe and backs up through the freeze pipe. The heat is exchanged between the soil and the cooling medium.

Continuous flow of the cooling medium maintains the watertight ring of ice. When the ice ring closes, the water inside the ring cannot run off which increases the water pressure in the core and indicates that the freeze has achieved closure. During the freezing process the water pressure is measured by the manometer at the head of the dewatering bore.

It is known that the growth of the freeze collar is homogenous in homogenous soil conditions and those not influenced by tunnel temperatures. Values below -5°C at the outer circumference confirm that the required freeze body thickness of 2m is achieved. Further it must be validated that the average temperature within the freeze body is equal to or colder than Tmin = -10°C. Assuming that temperatures at the outer designcircumference of the freeze body shall be below -5°C, and under conservative consideration of a simplified linear temperature distribution versus the freeze wall thickness,

Fig 2. Location of freeze pipes and temperature measurement pipes across the length of the 14m long cross passage

under the Suez Canal the minimum temperature at the centerline of the cross passage core has to be equal to or colder than Tmin = -15°C.

Top: Frozen cross passage face; Bottom: Extra support frame erected ahead of (right) cross passage breakout

At the opposite tunnel, where freeze pipes fall short of touching the opposite tunnel lining, the freeze body has to grow by at least 1.5m to connect to the opposite tunnel. Due to the circular shape of the main tunnel, the -5°C isochrone has to validate the 1.5m connection zone of the freeze body at the opposite tunnel where the shape of the cross passage connection is an ellipse. It took, on average, about four weeks to install and establish the freeze around each cross passage.

Cross passage excavation

Once the freeze zone met the design criteria, track sewing and core drilling was used to cut out the precast segmental lining and create a 2m wide x 3.5m high breakout.

Sequential excavation of each cross passage advanced in 1m x 19.6m2 full face rounds and was supported with a 25cm thick layer of shotcrete reinforced with steel ribs and wire mesh. Excavation progressed at about 1m/day. The primary lining created a natural load-bearing ring, controlled deformation and minimized heat transfer to the frozen body.

The waterproofing system of a geotextile layer of 700gm/m2, a double PVC layer of 3mm and 2mm, plus water-stops and injection hoses was installed. The cross passages were then finished to a 3.8m i.d. with a 350mm in-situ concrete lining with reinforced collars at each tunnel. The final lining is designed to ensure water tightness and to carry the permanent load once the freeze thaws.

Construction of the cross passages was a considerable achievement for the Ismailia highway project which was scheduled to open to traffic by mid-2019. n 33

First application of ground freezing in Singapore Just as a freezing application was about to start in Singapore, the freeze supported TBM railway drive at Rastatt in Germany failed (p28). This raised urgent concern among senior engineers with the LTA. It did not though cancel the freeze option in Singapore which has since been successfully completed.

CASE STUDY MAY 2017:

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onstruction of the 30km-long all-underground Thomson Line MRT for the Land Transport Authority (LTA) presented the first ground freezing application in Singapore.

Ground freezing at Marina Bay Station Overview of ground improvement regime of jet grouting and ground freezing

Poor ground conditions at the location of the Marina Bay Station required ground freezing in conjunction with jet grouting to support excavation of the Thompson Line under the North-South and Circle Lines in a double deck configuration. The freeze allowed 20 foundation piles supporting a 40m section of the upper-level lines to be removed for construction of the deep-level Thomson Line one above the other. The work was completed under Contract T226 awarded to Tasei of Japan in February 2014 for Sing$425 million.

Technical details of the project’s freeze application are available in a technical paper published by TUSST, the Tunnelling and Underground Construction Society of Singapore(1), and LTA produced a YouTube video to explain the process to the general public(2). Completion of the contract without any ingress of water into the headings, confirmed engineers with LTA were right in adopting ground freezing to support the excavation phase and the critical underground infrastructure in the zone of influence. n

References 1. Application of ground freezing for mined tunnel in T226 Marina Bay Station

2. Ground freezing to play a part at Thompson Line Marina Bay station 34

CASE STUDY AUGUST 2023

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Complex soft ground excavation supported by ground freezing takes the rail route safely under the Isarco River in Italy

Brenner Baseline relies on frozen Isarco River underpass

onstruction of the 55km long Brenner Base railway tunnel project, connecting Innsbruck, Austria and Fortezza, Italy, engages the full range of excavation methods and their support systems.

One of the most complex lots on the project is the 2.25km of twin running tunnels under the Isarco River near the southern portal in Italy. For a total of 4.5km, including access adits, the Isarco Lot is challenged by the soft ground conditions under the river which called for ground freezing and jet grouting to ensure a save excavation river underpass. Freezing was selected for the underpass to allow the river to continue to flow in its original riverbed during excavation and in that way preserve the flora and fauna in the area.

Construction began in 2014 with award of the €301 contract to a consortium led by Salini Impregilo with partners Strabag, Collini Lavori and Consorzio Integra.

Following two years of preparatory site works, including construction of access roads and site installations, excavation began with installation of a liquid nitrogen ground freezing plant to create the freeze zone around the full profile of each tunnel tube and stabilise the predominantly soft ground geology between the 60m-long tunnels and the riverbed. In total four tubes were excavated under the Isarco River. The twin tubes of

the Brenner Baseline project will connect to the existing railway network in Italy and two connecting tunnels will provide the link to the station in Fortezza.

To establish the horizontal freeze around the four 8m diameter railway tubes, two shafts were excavated to about 25m deep on each side of the river. Although technical details of the freeze installation here are limited, excavation of the first 60m of the twin tubes under the river broke through into the reception shaft in November 2022. The second 59m freeze-supported open-face excavation using excavators and hydraulic hammers was successfully completed in August 2023. To finalise the contract, the four temporary construction shafts are backfilled with the project’s excavated material, and all returned to as it was before the works began.

At the breakthrough of the second river underpass, Alessandro Marottoli, Director of Proceedings for BBT SE, the client, for the Isarco River Underpass construction lot, expressed his satisfaction saying: “Completion of the underpass tunnels is an important milestone for the Brenner Base Tunnel project. In the final phase of construction, where we are now, it is crucial to restore the areas affected by the works to their original state.” n

Route baseline railway under the Isarco River underpass (Fig 1, below); the shafts excavated to support the river underpass excavation (Fig 2, top right); and design of the ground freeze established to support the permeable soils during the four underpass drives (Fig 3, bottom right)

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STUDY: Excavation of the first Minneapol out of the ordinary is/St Paul LRT line for the time. It required to the Twin Cities management of early application airport was a project the tricky transition of a specified dual between open EPB-open mode make, and was and closed mode TBM, with one of the rare occasions of an a decision for use of a Herrenknec the contractor underground cavern ht TBM in the USA to with a flat crown. market, requiring electrical systems It was also the first professional adaptation to comply with USA power supplies of the mechanica and safety specificatio l and ns.

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Most of the tunnel and fine to medium grained, station excavation lies in favorable, St Peter Sandstone, well-rounded and uniformly graded a deposit that extends (45m) beneath the some 150ft limestone. Groundwate sandstone, about 2m below invert level, r lies deep in the relatively impervious and a thin layer of Glenwood Shale water table in the creates a perched open bedding planes Limestone and in of the Platteville the overlying alluvial and glacial top soils.

Top of rail at the During a site visit center of Lindbergh Station in July 2002, the (11.3m) beneath the is about 37ft first 7,400ft long o.d. (2.25km x 6.5m) limestone cap, which x 21ft segmentally lined thick, and creates is about 30ft (9m) finished and the running tunnel was a flat ceiling to the Herrenknecht EPBM station excavation.

(152m) into the parallel was Client for the undergroun drive. The Obayashi/Josome 500ft JV had also started d works at the excavating the 14-6ftCASE hnson Bros Metropolitan Airports airport is the of the 525ft long deep topheading plex Commission (MAC) STUDY: An team x 60ft and the design for the design-bid-b ning, com extensive Seattle 12m) Lindbergh Station. wide x 40ft deep (160m uild contract is x18minx began light rail city plan nsive option led by HNTB network the Corporation late 1980s with specialist plicated the Seattle and it is expectedThe in subconsulta least expe of com with excav nts Hatch Mott downtown MacDonald is highly abrasive running ation is a story to provide the lk geology. and ventilation; bus tunnel for tunneling The alluvial material of cutterhead toolsadvanced tunnels of the LRT pass directly accommoda of CNA Consulting project s. Today complete changes beneath the pressures and across the central te airport n Cha four mandatory both metro the USA highAusti hydrostatic that at least two in oulders, lace LRT alluvial valley are tracked by athe tunnels bus beneath servicesthe taxiwaysand The contract specifies s Cityp moving exclusion will allow of NATM the were the treacherous favorable and mark(Fig 1 toptrains will be needed. zone as the TBM where conditions right) and electric in abrasive alluvial materials on the underground comm of the Dalla application the beginn with man entry inspections in areas TBM tunnelers ined the tunnels air pressures of less extens on diameter. ing of severa Y: The story and another comb in greatly conditions awaiting An order running Diego under compressed Transit, includ of thations There San STUD of or, in E size the l TBM intervention ents project LRT safe were corrid ever CAS outfall t the and ofand ing TBMs erns, built. system the, deep placed for two new hard probability fornot South Bay ocean ghou arrangem LRT station Sound we visite too many station on the highconc While sourc bar.

Beaco with Herre to this was nd throu n Hill underg d the two on the the extens the LRTthecost than 3 funding Added borhood machines ent ing supp nknecht rock gripper mid-1990s. n ofthrough n and AlpTr ion man entry, Herre round for the U-Link signe undergrou south constructio desig andthe TBMs was ansit Lötsc and neigh for the developm for an air assisted During activity Tukwila nknecht rock ly of two new for an among ntal during delay and Northd a lease to ing and project WCSO said the shaft. possible chance Y 199 2 the cant as -debated seismic contract Link service 2004 rankingin this Link agree hberg; TBM TBMs work environme life, plann projedrives signifito tigate ind,”the ed The first is in Reach 2 at about 3,000ft from Mike Robis site visit, design d the driven ct in Switz . Time extens beinves ORT: MA n on its much h 1992 facility’s ions; s that share mentand licate the ing is the critica theHerre resulted s tunnels comp with IT REP Dallas-bas for however, Marc fact actio through subaqueou ns weretunnel erland Eastthe Nanc on, Resident first point space difficultntly optiorailway the famouthat Herre rs, thein Canada with l facto and of the 3.5 mile long SITE VIS began seeing real system in earlycivil contracts most nkne y Cree Constructi of contact St Clair conseque with the us t to DART vario TBMssinMount nknecht highw ray and in assoc Huitt-Zolla k and fortraffic run under and geological section through complex port was this contr cht in May two the 1990s, along on Baker Ridge in Denmark. nine mont could comm allas consultan erns as Presi Figs 1 and 2. Plan dent ofproject thethe m of railway conc iation withWest Area CSO Manager for with the first streets act public trans Creek facilities tunnel to outfall, which passes hs was otherof the Storebaelt SEM tunnel Bellevu light rail dbreaking on ile starter syste T) LRT. SA andBob project Zollars, and general both projects EDT for manu a signifi itand building and the South Bay undersea of the Pacific Ocean e floor . comp in factu For the and Hatch the cant firm driven (DAR groun Sound in the two beneath 20-m rers. After Line’s new it onents act edge on with Mott MacD with Delo management with JJ&G, the Seattle Transit LRT, 11ft i.d. machine y, built alluvial materials of the consulting taking n Ham of the Nanc run from Rapid Trans million contr milesct.long, the busthe it all started bottom in mid-M 3.5r proje depositsto an in tunnel truction Expresswa delivery offers from iated At nearly s Area mix of thealluvial a singl onald for WCS pton Asso of the 312ftay, we plan y with the starte through a complex end of s. for cons 67-mile Dalla work on its $86.8 of the TBM water recla its assoc four-lane to launc e site office The cut the facilities plan studied ciates , tunnel a ages. n is thatover passes O. and July, the d (95m town n from Both licatio h tual s ent deep River which will the first 1989 starte ) deep a implemto statio ased location even projects and the Tijuanaincre constructi mation cente BER d inestuary to by comp TBM Rock downipal the be ahea Chicago underground while acros millio of(P/CM) washed at town McKee (CDM). mouth SITE VISIT “We RT: nOCTO depreresse is to beofat the The princof manag d of our dale Shaft by at tunnels on itsREPO be down Healy of flows fromon of the pumpr (WRC). At one the R.M. Claytare Dresse thes, seabed and r are, in fact, is to to from sands Camp REPO RT: lth baseline VISIT $18.8 Cityplace runningSITE the ng composition . granular 6 by andclays on Nut late 1950 on work onwea end ay statio d the built runni River the 1985-8 and DECE shaft for the of twin tube y ahea progr cons Comm of silts on was Nanc and freew m) n is unde fine the Trinit sinking MBER d of sched tructi tion, am. of thefrom secti sizeable y Cree ado starte -lane ranges 1987 way. cobbles shaft treatment plant grew, a second s distinc and rway to WRC eight (6.5kin which High path 3.5 miles elps of Color bridge over the capital city the WCS on of the new, k project. dubiou gravels mile sewage of the the region the deep alluvial westFrom a 200ft being new underg element and site mobilizatioule at the mom first oston, theestab loose ofNorth the 4 kee, shares As dedicated At the otheraccept ess the LRT ts,lished forMilwau After primary Boston’s etunnel fromround Hensel-Ph 1952.tion MassAna O project will anticipated. n, but minin ent with we are succin has arethe rity, chuset 1968. nd each the in to build boulders street Seattle and the by Quincy Massa been treatm the end, begin autho d o large beyo outlets act in futur looking pora Island shoreline, ’s the the ing just charge Chicagss ont . At the answer toTBM to for Island contr ent buses and Transit the seco is sinking the back from at Deer the ged through short for 60-70 g is the critica withit has cities by incor do 1 mile Formation tly built toplann Parallel 1.3 TBMs WRC site, plant for along network, urban rema Diego in on only set about round Sanfican was een proce l waterfr thesigni Discharge ft (18- 21m)/ s Area Rapid LRT y (EPA) thethrough week plant schedwas betw -the-ctraffic an uphil nd WCSO TBMClayton acce mile ating US pass under the Agenclace, to belowisofdischar an long maximum.

(2km) , day rge with lock onconges ule. We “Ideally , the Dalla a closed, 230ft frustrlarge the waste ncedand designed those ems, ss shaft Obayashi/ integrated ation l gradient tion. about in beention ing,1986 a fulllong discha Cityp streets Protec will mile influe often among ns probl the expect tunnels At sion pressu three seabed the screen will is be For DART manage an by excav day the one recep the of mental from and better to 50% of week uling theends , up 8hr ent courseNego rized tunneli operate below provi to the s. tiatio than leading afternoon in for ate 23,00 central district which Environ n caused to 158ft in the watertion shaft to have lopm shifts Station more 45ft at up harbor. the buses d the the tenanto federa expensive et . Part of main deveits water and lsched is a main of little ages in y. in 1983 thes,pollutio shield Shaft will 0ft (7km 2). n.

(65m bearing .ground statio The ng215ft n issue present 4 ce on each/day, will 1 and offtenan In the waste out of the 6 days/ about ,” said John the agree would e into (FigsLRT the streets ) deep Jim once a day take eDART Budg someth arduous, ing the ,agree nd pass desig sea level up advance first mile/hr place TBM, sswa ded. rgrou south North Aven) in of anand dissolv ce contr and techn takes mach a long, at this point.

Atkinso rding to sewag MacDo to its 148ft will carry ing and iently commu ment mile/hr in increas s and tideive Pionee 20,500ft oflaunc ician on accotreated nald, Project and that this is ill-foun the Expre plannof act with tereach hedr at with Herre inen,on“but there e the loper elmed.

DART: to dilute n with unde ofebbing traffic flows comprehens peak with athe insuffic s, but and deve period (6.2k er overwh the Rock ue side that to arrive with complex s proves many are (45m) deep nt forl abilityat Manag Cityplace delay nd statio studies mach nkne been s. nkne to one Herre full-tim ’s natura sky r of beache investigation about either Parsons infor sitergrou sinceunde dale Clear Cree m) chtscrapers along deep tie light an enience backs on the designer 12 e Herre Intensive long and time The , owne Manageme green n on better excav together cht. We ine. We also have rs, onethe Waste anchoring by project on harbor withnkne “Two TBMs the tunnel pany cally hassyste Tunneling these k the uphill gradient prepared 7-11 conv m beral finishbased the solutio high costof Constructi reporttowe chtwe need easy will the LRT a majorit both r began in ated and they date, in as far ofas can tion shaft geological to prick are a minim route and recep hland Com waste biologi to re that, chain caused tectu the WCS access group r contr indicate Atkinson/Dillin November will supp pay a fixed cutte of s, CDM to t outfall. To outfalls y act archi . been given of the startedate.al the Sout Science problem and of the tunnel Director ational rdfour ” or pressu reaches to theum n, ties cost/yd g the Assembly requireme deal 1986 when ventilation effluen d ly all the 3 intern face. retur gham authori Martin, excited to have construction chose Knowinthe by the isOintunne pass through individu Engineering 1996 s and lowest of of rock JV the public completed Also, long-di two open-fa dry, lscompe the Guy of thewill asntthe cutte to lie stance14 long sea tunnele ly under uledan the t tunnel work and said consent ibute 1towa oving paren to get excav an avid it takes nt 3 are eight compe ofwon theTBM to get predicted, first F r need civil and case, contr tent ground “We are contrac hold treatme and machin the sched of large, slow-m s.” the upper saidced current decre other below the are about byOften Bostons,’s t with the ation wouldforReaches geology.

Ken at Rock are ready only inn. which there water millio with e facility h, with deadline the, we Johnes material part $61.6 million ting bids at $44.2 the largest theaction. quite Indifferent breasti 1980s, dale Shaft store sible operation conscience into last and t $40 the in oper of WCSof are n whicand ng plates taking the more respon face ston, sandy d abou of 7 Nove ingravelly worldw be ide, ated ia.

O the thewet ation and into contr tioncost to mber softer scale tunnels much seaonmust usual 30-to-3 Engineer’s Estima million, well , theOf the statio porous City’s Proje in agency of the gripp act.in“As operati ofgranular Founda forcengthem rolling , Austral anaestim nts, willpressure in theervarious runni a the State a job of this on.

6 month constru te. Instead sectionmachin ons.” in hydrostatic 2007,” well as conditi in Thefullvation on sued beSydney ct Mana barLaw ireme to was 7requ jogger and Agency secti e. lace ction ed nt Conser and its beach of ion the scale, nd going anticipated the n The Cityp are constru was “techni s. edown Protect 2 and 4Act me, ction period , Seattle Metro, proposals, TBM drive ger for the all treatme tight 17 month statio m mentalReaches the schem now involv under ing costs undergrou forservice cally syste the one from material sewer Wateral sche silty for s plan has with flow from expected. the client, s, the contr and sals progra Cityplace nd sections propo only e CBD is also Seattle superior andwith starterl Environ origin permeable by early l inches ted Robbins CDM facilitie Federal Clean the )Federa r Island a town r theless the reduc act Federa (32km 1972 competent, eleva sued -based making most econom ed ,with 1990. To m to have the system imposed a Apart of the 7-mil to spare down Unde turnmile on Deer an Island in Boston undergrou n of earlie 20 ng themore State.

In charg ical.” the y on n Deer meet place t reliable the in enforci (right to Robbin ) by pressure. in was deliver on not the (EPA) for(11km this, Atkinso millio service ary machines, s ) moderate harbor by suing at abou y easy and ge taking d Expresswa more an order DART the $218 d when down versio sal for atedded this secti The machin and second n neede one and deliver respon quick. t 7 miles impose ver esse ity rundischar propo was EPAestim 3, thereunder es are quite 1989,ces andcarried 1depr ed quickly for each tube, design d two Island ns howe After primary 8-10 miles out to in eMay 1986 InResour was to of reaches and thewas original rground for abou schem of the nAuthor Nut open-faced finding different . conditions long tunnel. ged estio (CBD) and expe nsive the t and ed, built suggestio . The median mile gravelly Water e excavation (7.6km) porous, rectify rtmen district the a sugg foundIn District e theTBM an CourtMassac ran unde plenum, will be dischar 110ft of water where 5 Thesor m to abov the backho shields. To provide from the more familiar The geolog to be husetts progra effluen business oval for such s the In t using a no ture into the way median. the Depa man e paddle nt, de can freezing. ent y be High strucentry which had llytoat-gra central limits in about can naturally dilute of ground on the treatme implem -type excavaoptimum face access tripod of clay with the is mostly over-co . Appr n. the assistance a alternative ) antia had the harbor inter-re the State .beyond ocean without nsolidated to require 1999. millio or at grade water table .7than (MWRA $1.1 billion cheaper chamber, subst no$828 of the is expected sea built two other acting hydraulic tor is mounted on , ted by ment entry sands, silt 14 of Pionee runs 47 balanceLRT lineswaste (Fig 1). and rejecman d at later 4, safe n by and cylinde a ruling r Square Stationrising close to the and thetoalign machines face. ical were theecolog situatio denied now being built and reaches 2with Theremaining is price Washington the court along ed.the water table to this design rs. Robbins has surface south the air to help by holdthe (Fig 1). North rade There will reach DC Metro complyof compressed is of-ways residents side of biodeg todegree , one used scheme Coordinated e was and of the Station Caracas Metro worknd. y Deer Island facility in 1974 and over consoli well below the tunnel thergrou either rail rightromis on the sswaed unde time to lose. newly ,formed , the the other scale busin be of noess boxes in 1978. gallons/ dated materia Expre existing elevation The to e left propos thethe , the 1989 a comp used on the has central ts dated in ral and the dry ted, ls can be thedeadlin sswaydivision on costthan 1,200 million part of 37 June a short nsultan system such mmo ement In its very hard.

Expre sub-co When integ comple acco The 21ft (6.4m) manag y of more l and constructi mral ged ative. From lace the Cent erciaers d be atedcapacit progra Being anhave own ts enga a peak woul Engine diameter, (HNTB) g. and estim comm North At Cityp ptable altern sits r an doff a ultan Kaiser the y thrust cuttin d was 140 ay onstructions, with tonne, 600hp capacity of a majo multistore engage by cons n & Bergen highw truction boxe is no acce route follow Cityp lace, MWRA 2,400 tonne s Tamme mme/cthese two shields have designed their cons the Needle have s rising itsa progra via the 20 project, million, were through Howard Both as district, comp t and thrust rams 62 built.1988 April 19 passes development in be t to Departmen y program. of $189 yet which Geotes ential Highway which is plans.

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collapse it not back CH 1999 under control after Authorit•y Construction Manager: in now why was in-depth of an Water ED: MAR subjectTrent works at Heathrow is theSevern The to•that Taylor Woodrow station excavation &Safety being Client:the sites.answer now UK Healthr: G nnel portal H Hill & Sons tunnelling : Eurotu faultless.is ners: Contractor: investigation by about October 1994. •The Enginee the intended of which is ingreport ofClient • Design-build ENT: JULY r: Geostor the The £20 facility in its Desig Consult projectoflooks vicinity of men and 1983 when •(HSE), the & Co of the site for the depth andtunnels out uced from materials and for million project, kept million yet.

• Contrac carried e Ltd simple”, undertaking the and andExecutive Mowlem 78m actor introd (TML) Balfour Beatty £15.1 is “amazing d 1994 AND machinery ventilation, with John months taken for several tors: according ass awere Contrand maximum a joint wereLink of Calor deep x 1.8m diameter of • men bore hole reamed ly coal interest, (6.5fissure started brought to the application Contractor: being collected firms to•appear samples to Tom The Resident Gas,a with hatlling system -Mancheby eight unlikely andthethe FEBRUAR surface via two a 10.5km h the wet • Thyssen and Conoco,with is still Paterson, Wirtha reamer Trans 160m. Core is impressive 60% consists Mining Engineer to build tion (p56) the start 14.5km 40% tunne were complete /Pigott Consort l throug Carsingt resources aton Material evidence highly likely long spine roads examina Y 1996 contract of legalthe tunnel ortium contract . The top . ners: t at chalkproject readythe to tunne possibility share, has and with gs.detail for constructed in as a result remains of alluvial ium: Shafts to remainin , causing view, the meticulous. drop coal isCons l Desig from • Boldon 20m site and the identified proceedings al in headin the ls) production onto hard planning to store g the the and glacial longofaqueduc rock well below the upper geologic Tunne moved through the tunnel Tunne attention mile)ions ct Japan was Drilling: Service point of that ethe of the a conveyor g foron next 200m le deposits and the coal bearing scale rtium landward the in the crossthe slightly to avoid stages and instability tenderin u d’Étud into severe indicated availab technical Tunnel to conne for the parties involved. made clear toA conveyor adit chalk strata. remarka condit is the an event for transferring boreholes adjusted • Conso • Fairclou While (Burea ire has run sea andofnotexcavati through borings t to be or struts and readilyon onto aon to construc rom a system will bring which stretches Upper Cretaceo conveyor hen gh: Cavern bly quickly. e: BETU ion whalings in Derbysh alignmen in either their under Channel Calais in France Therefore, it was the driven mostly the coal the spine tionof nald the early The Francbe us complet g props, isedup the two 1-in-4 need for s were tunnels Jubile theunderlyin east under for the roads and hauled Seae and to ofs, andsystem be used area.

McDowith wouldshaft undersea avoiding d to In January drifts to emerge areddifficultie years behind have the North attending an all-party-organJune to Projec affected Mottseries tunnelsrescue the surface could not Denmark as two journalists t team, Lineinto UK: Grit updiameter at the was Exten in Englan 8km at Gascoigne1981, contractors would Gascoigne Wood 60m as comp ng in beThese TBMs water much ean end construction. angles t, the of as Dover briefing in late may granted by Woodplanning six exploratosion and (Fig 2). When Fullface Ashover the Londoallnonfive From appoin site where all the permissi andthe French at shallow Germany. amount may to Europ dateand l and h the lt projec JLEWest It excavation visit and technical was Glanford of core constr ry coal formines budge Under throug ease Strait crossi to the are producing g tunne a difficu natural ground is also necessary to e, planned pt that of the large of access site uctionCouncil es, these dipping the excavati about the causes handling, storage and loading main series groun t as thedchalkted byborehole at Borough ent runninThe ls. NATM because full capacity Seikan schem passing originally1970s attem use the was not well scheds, it was found contains several ofby the water pressure to manag on of theextens facilities 115,000 1996, that questions by mudston equipm late 1980s, Selby porary es n for marine would as much. lty , awarded of tunnel. are located (Figs ardoftunne chosen theonLPG.” s and the lack bands two approxim ion,million mudston new of Applicationas its progra pre-grouting. e cover ule. deliver aquifers 1 and 2). to contain with the or along lengths greatg difficu m 3 caverns will from and the costs thereof g tunnel costing twice 10 The mme setately expected, the contemexample. The UKedlandw cular fashio strataspecta 16marl contract and collapse principle specified and tonne ions had the a of runnin long very km-lo es, As coal 21.2m the however the 53-mo under soon , for ground a x rail for Conoco for year, mostly for use startowned tunnellin is as spine roads reached in isolated d interbedd assoc ng hard more to contract s are: i.d. land When choosing sandston to do long The journalists tunnel The fractu water nth red condit (Fig used in and 164km Japan face bytothe public pressure, • that a higher funds t, except the storageset itself Authority programme a madeflint Central UK the Electricity not be by openin first mine at Wistow, lly answered. time. two 7.6m thensiltstones service one containe on the Water to the 2). iated cost , acts increa to in this storage Client of drill+blas Generating ofBoard of the survey 2was ed with section) x against at that twoletunnels, case liquid a tough central thorough briefing for achievement interbedd g, it knew coal production and butane gas facility, the ofsite : JLE also specifica Severn Trent 285psi, comprising an UK The use propane thewere ses Governmen at nearby LPG Transp chosen, calls for 100psi needed geophysical Marl stratum task. As theSite diameter were treated to a from excav power stations.(Fig 1).

A ation ed by high (252m 14 large 4.8m i.d. it had geology confirm the 55m Londoto Manageme work er. It was ances, was ort throug propane tochamb other notab connect Chalk Mowlem view of the current progress and to a visit it began with tunnelling of the soon weak, most t Depar began immedia vice versa. x 15.4m investiga In time or is large the Two civil John the and a n circumst perhaps liquefy the and French nt 4.8km, as importan Unde the same bids.

30psi in eable, spine h team constr tion let in late project’s tment to liquefy the project's to d wide the continuing to which at the crossoverthe design of short of roads In the interim thetely rground on 1). the other containin out due from the success the first of t consider ation of pipeline uction for • Contr and later the gmajori connect the remaining million contract butane, public fundin shaft(Fig conveyors 1993, into various sections four sea depends 3.6km and it. The was aligne contra lly an imperm excluded Ltd le for rapid also scarried under in the a signs • Excavdiameter excavation spineof to sinkand Its aquifers £2 “One ation. access ty ofpresence of actorsthus how mines. cts borings. During tion, ls under e problems expected aunderground at theg acces for investiga shieldwill transport a great natural is genera fourconstr g is grante tworoads deep 140m of the most tunnel al workin access for each highly suitabzones awith major geologicwas to modifi both enginsubstantand 3km of the 1.6km x 1.6m uction specify on-going works. Knowing exactly is essentia extent 66m which extensiv from aspects shafts, rail tunne the work princip engineer cavern, was main site d. ial their desig startecoal minesalong te to us rock on impor al propertiecation used again ed as they come decided to l. “Unlike eers: See a shorter more gases, excavation d.

Thyssen as the g and three on line andawarded ated. is also side workmanship andThe south drift tunnel is being Roadheader tunnellin All following the longto land By from s. Petroleu clauses other tant almost all following n-build explore inclay en-roufaulting, it was muck homogeneoalthough fractur be anticipThere theto end consultinsea of severa the contra stage, g jobs, we current quality of driven the /Pigott behind alignmeasily constr the of form, themore Consorti m we 500m on method. best the the site. what the 5.8m diameter borings soft in gault end. The headings. to pages tunnelling of water option, three under from with stored welcome l the um. uction ent 5th introdseeping Januaare ster.

Nine to two lofterminal based excavati Hill in ct tunnel the docum takes sump entaryCastleadjacent the sight s for eachmachines tunnelling, inflows were uced into surface Robbins TBMborehole downstream for itsof Manche supervision differs liquefied in their workdeadservices ry liquefied total 230-w Tunne construction with be ent was was in a large supplem neveran average of considered stratum headings. will based cavern landward tempera 1996, the by eithercondit workscorrid and end levelH Hill & Sons continue!” into the ions, is The need to cased about 100m/wk. the collapse may Channel was moved and or were orted to the scheme eek corrid long tion it was the ground high waterthe Chalk Marl contra lowering booms were fortransp on confesse Strathclyde drilled or by compres programmeweek ture 117 of theira stipula of Anderson nt would Theconventi below seais G or beingprayofit up to 90m the UKOne portal was going on before Boldon north where detail were made.

ICE conveyor by d Paterson included surface, n also is: the implemctor in the Drilling under explained in some tunnel, some 70m parallel, its originally Coal Board tionartthat Souththe out sion.would Site investiga and excav three the shaft wide, the muck was Tunnel Following a maximum 115m d. Tunnelling . equivalent it is usual from of site andentall equipme using portals grounad On the 1979 ofand l mentio be bound The incorporates oil well type is being 57 x onal 75% comp known, but it was times the be excavated using line ed to National plishm theselection lies during to ation to store ent 16mm the pump stratum through this out in familiar sectio of speciaarea of surface steel ropedrilling to accep ydistance m3 some the seabe a Titan 134 roadheader The the bottoms water along and accom flamepro now being progressed alignment to approximate themanin accele in finding for thet caverns e ofed lete. g incarried refrigerated provid cords rig. n was tunnels are going detail how downhill across the full Worthwhen an Of the the ration a beneath making about half and ing y of the work width£4.5 ly about tanks rather 4.5 ,million the tunnels The JLE depth. to workin available. of deep borehole whose is sufficien of themillion d with at a1mlarge intervals tunnellin pressure logistical necessary servic site 30mm thick many the rate of progress was awarded water inflow progra original. slurrie and 75m suited UK s as strata, with the possibilit belt.g The t to containfor contro vessels. Cheaper and that it was sinking standard contract planned • The Projec thanshown Anderson construction al in in so at Strathclydeto Cable the ce.

Faircloug is different from the t, generally about 50m/wk. Coal in distan t team g the to be practicmme s highly tried and readily the LPGlling groun methods availab themis under was three long holes 1km h, the stillthe Measures cannot be extractedfive tenders. Geostore the aqueduc Belt for dispos as to make minim system is cost lowest ued conveyor ered.

Coal estimates great to store whilein about l shallow supervising UK side, of runnin pressureas reason larly the ising but not d movem of appoin remarkablyof d until the cross theundergro le contin North Tunnel is acontra were well the cost additiona seepage waterable g pond grouting on the scheme , a licencee ctors in largerable,” French being encount particu of adit connecting steel These used on of settlem ted ent and geology Robbins pumping company comp changed und rope Projec NATMAqueductation with several settlin ent, nearly methane capacity said Mike were accep from or reinforced specified theGiant shaft rescue trains, of the TBM from the the two conveyor which allowe facilities. techni belt t the spine roads and ted consu excav Geostocleted tunnels.

Manag on ation ofir and ground In some access The cavernJLE. have extensive designed cal doubles speed with two ls Liquefied all have Engineer also What had l advances most Reservo lting sea Smith the k, lling rapid of stable d prohibitiv bore time steel been Applic cases er ton the which roadheader obvious, canno tunne hole ropes and for most under , JLE’s connecting diameter supervis for Const tunne gases • been of origina enginesuccess and sealed, this may To comp 57mm allowe e. has l in logica start,tothe the mine above is 1. Carsing To and prepa allow grouting fully tstored the same for thethe ed a ersexcavation ers and pressure of several require extensiv supporting tunnel regime to ensure modification /week the detaile ruction Selby ensate red the tunnel completed. construc predic used initially the techno ng high speed 428mFig operatio spine lightweight LPG caverns, On leached be jeopar cross while at cing service roads d indesign projecgroundw under alling area which to tion ted settlem e for areas 1in-thick lex chamb clearly most expensive, um and breaki 60mWistow mine t prograater. “Wens and ground The steel dised by fordocum of the the The chalkbelt. a projec contra ct many years s cavities in salt t s through ropesincluding in northern a maxim a maximum 8h high,alteration the comp ground marsh record came online in April ent may our are formed amount of the original scope of works is mme deposits condition spliced regime the advan excavation where t oftogether one events there entatio grout of the At its this in size side of findingcontro g to around the toadvance under to form an France, finalbut to be almos thethat still prove have forand engineer l. the n.14.5km built in the construc isrope suitable injectio Cliff. This a purpose The and the consultin length, with the expected methods caverns of the the UK 7 days/week with eek) buildin are within proven been . Associat endless dealtwo accele geology tion of water comp concurrent er, which had of the conveyor at -built undergro each x 30m deep cofferdam in three stages:diameter too speare will station g side. unfore edOne be lexity, come intobyn ground of the shift/w the contract and water contractual ration construction ntally the tunnel; easydifficu of the airport seen This is done of itsits und clause most advers no s include at Shake al working treatment (24h/day, maintenance kind month task, as longest used to curtains groutingalleries water. ation in operation their own. over chambbefore arrival excav of driving Central Terminal Area (CTA in of g methoabove, the e in Europe. ete segme The is useful s whenfacility TBMs lties.Paterson explaine South Killinghohas between River Humber, a newOctob LPGerjetty Two effecti was“The ds used caverns.

1994onof re in advance are built; and radial 1, 2 and 3) to almost totally permeation the princip of the six downtime service Similarly, pressu the collap over the grouting olted concro.d. 8,036m. geology were being d:the recove ness complete on lme, and At the nes. ve d. rings NATM the site neither non-b pipelines marine Terminals on must on the the ry progra of unrelated, se enough connect the l of machi negotiated.” water as the groutin JLE includ grouting be compete excavation gallery strengthen ges and grouting launch a fully to remove the extent tunnel muck will also km each is expected has been complete nor g, mmes Airport which facility to sea tunne 22km of 179m/week nt e concu work extensive excavati encompass and TBM allow the Conoco loose a to stabilis Express but ofrrent, Only by cross passa had to share cing after the lining vs be necessa course and 18.77 Settlemen and to complete lined under l average was l south. e and water disturbed ground. grouting of the the roadhead refinery Rail er on and the Because the geologic Heath compensati an immed also ry. advan 17.36km collapse and the tunne rowmore and Since limited the t cont requirem g ducts al propertieon groutinbearing groun l site are so iate and Link tunne introduction Groun with the the effects tunnel, best overal running ent, the drivesstanding at the edge of this huge excavation rn slurry relievin projec support A Titan E205 of the Jubile s of rolthe d movem the more responsible l progress l to porta n times gs.

TBM, marine t. As g for mitiga d, of predic bay has been importan t, a geotechn roadheader e project ent side, mode pressurised econom ratesbeen consecutive interce job, Mowlemscale be appreciated. "The upper the UK induce in the from porta ted transportatio g tunnel headin Four which South ic its contra one French establish excavatingteam volunt reaction, the Tunnel the have dpiezome its that bid the couldWork of by excava Tunnel e (EPB) and ed,pt ground ical volume losses ting work runnin On the the 9m wide eight firms arily instruc JLE projec the most critical tender. ters tion has Channel cross marine water-bearing ground re balanc Of the Waterloo ctors to stop to measure equippedmovem mining with ents as and x was soft outer lowest 20m second tedtop heading four hand 53km long and Londo thethe and through NATM 5m high ground water they occur. beneath t team. The Line, concerns for the and earth pressu many lateral Compen stabilized by 1.2m with shaft ducts won of the integrity er 1981 gravels work at ,some d the rescue • The x plishe with visible is supported and running 30m deep central on years.

Septemb section re relief access sation and safety n Bridge to of the oldest bands important as it does 60m diameter Comp ls. in shaft, pressu accom original ed in four piles which interlock review of marl started 1km of 19m diameter grouting tunne Fig 1. Trace of the Geological , historic of the and and flint presentensation stages of diameter the is on the one toSecant NATM ges and main bored to be complet different works. a comp ally most Alan Powderham, under grouting and subjected prestigious, the only work had designed for JLE in the About centres," explained all of which were access shafts superimposedpassa areas of lex chalk 1.06m tunnels, and to the is princip techniques Mowlem plan was the four portals the three at that limitation exercise manag London, outer platform linking of the Foundations time and been completed NATM surveying yed The from ally to ensure ement tolerances most stringent concourse and dersDirector Managing work collapsed advanced a tunnel roadhea decision-ma and co-op in multi-level thegmain tunnels damag the works of Mott MacDonald restarted although revise the delay headin ling projec ever before • The ce systems emplotunneldrive excavation when Strathclyde Geotechnical Steel Division king based erative all-par d in due imposed e provid had a ea t in the Anderson fact representative on Grosvenor guidan Asses In using ct designer's and dama unders ed on city. course lead ty sea. in sments six Aquedu and ging effect by extens on inform Markham , predic tonthe convened PortaltheC instrum of all buildin under the mounted that Carsing Compensat servicein ation Solutions Team ted on the started at the so-called entatio ly meet French gs within of the 10.5km n and ive geotechnica Tunnelling ion grout the 12.4k 1mm settlem B and D in analysis. collapse to engineer m on did actual the UK and the shields. the ent conto 350m cross sections ing arrays m under l computer-b and at Portals immediately following the “The of dinal and Harris, ur along ground way forward. "The junction was within February 1982, at A in April. under ased a Direct aim,” explai and in economic Fig 2. Longitu route define the Westm a safe headings level. ned David stage, or of the by 900mm and finally the princip tunnel marine on March, s a inster area at an early company Clay below is supported the 60mm London d decided conditions, on comp al geotechnica installed which step in GCG as nts of It was line and create d ground diameterplan contiguous piles ensation l advise from five establishme side which a predicte r to of the 20m below, the grouting, tempo viewcliffs • The s on the UK comprehensive continue a further chalk andon, rary grout “is to keep JLE from, ng m3 e a excavati formulat capping beam at lagoon l headi the white ing shafts tomillion the method of Secant piles.

With "A substantial concrete collar e Tunne foot of ating the some 3.75 incorpor nt lining. at the a rigid UK Servic and tightly site for main forms and permane ground the surface e for the disposal what is an small roof support Employer, in all the 79piles together. manufactur linking nt of the were Report site. of muck TBM in in both the recovery ideas ies agreeme of CIRIA working s’ "Originally, Howden a large Practice endations high confined nt casting factorrecomm excavating of on Contract d based nds instinctively segme approach g - Improve Fig 1. Plan of the ‘Tunnellin nts were x 65m," said Powderham.

• The ries where thousa Gascoigne Wood and the general nts. 65m box of about y drifts and the five mine followed lining segme count shaft sites; UK factor contract documewere to tunnel Thewere tial in the Inset: Fig 2. Main ated precision at high rats. incorpor of the tunnel design features a poten day sections rock, the need for produced Grain had Although nt nts per 55 Isle of near segme on the driven in compete was expected d 4,42,7 of 1,152 requirebe roof support output immediate ced the and produ within 3.5 years. on of the 37 42 nts segme now goingand lengths installation units • The thousands of and other , track many al cabling of electric

REPORT

tax in the sewerage the water and served by rates for and cities the lowest clean 1997 one ofMAY 43 towns project to REPORT: had paid payers of VISIT ians SITE Boston ar, $6.1 billion when rate d water flowing to a ten-ye : For years in the 19080s t ted pollute contributed dramatically (MWRA) of the earlies that preven changed Authority was one programme USA. This r project Resources the TARP Milwaukee. tts Water Boston Harbo Harbor. After including Massachuse Lakes, the of Boston on since, pollution of the Great following fully assembled manyback-up Michigan up severe with Boretec and its Lake USA before EPBM the and into in go Mitsubishi behind ups the Pacific Ocean from Chica on clean shaft and site tested with t CSO polluti the 200ft deep access and larges being lowered into

CASE STUDY

CASE

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Direct by Design

Fullfacer vs roa

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t management San Diego effluen

CASE STUDY:

Application of a TBM for developmen in North Yorkshire t of one of the was the first use twin spine roads of a TBM on a demonstrated to link five coal mining project the significant mines in the UK. The 5.8m advantages of Robbins went on diameter Robbins the technique to supply TBMs to over traditional mine CASE operations the roadheader excavation TBM non-circular TBM STUDYworld for excavating over. Most recently : Excava rectangular Robbins has developed and an estimat cross sections. tion of the ed half the first a new cost of creatin ever purpose built also provide LPG storage d greater g the same security for caverns in JUNE 1983 storage capac these vital the UK in CASE STUD ity in tanks infrastructure on the surface the 1980s were built facilities.

Y: JLE, the SITE VISIT turbulent at . Underground REPOR T: MARC London times. storage Excavatio including Undergrou H 1984 n the Big nd Jubile and Lond Ben clock progressed e on Bridg tower and under or along Line Extension services project, side to area e mainline railwa the Hous lived throu es of Parlia some of limits of s of south y statio the most the gh exciti ment; ns; and impo created excavatio Underground and east Lond ng as passed well as new metro rtant landm on, system. n work under arks of the most s colla Controlling which until the stations the city, pse he Selby coal critical unde excavatio then had rema River Thames labyrinth mine complex challenge on the conc of unlined in four times r the Waterloo Yorkshire was n and urrent s toget tunnels, driven designed by the settlement ined outside Heathrow ircuit and • Client: UK National her with SITEclosed-c UK National Coal the techn to bring metro in chalk VISI and loading Expre beneath Coal some mana Board mana Board (NCB) TS AND terminals 190m ical cons ss Rail the flatland to connect five ging the tankers for rail and ging the • Consultant: bank Link proje ABRatIDG separate mine sites on the south of the River truction National Coal budg Immingham. impact road - at Board Wistow, Stilling Fleet, Humber, ED FRO of the • Client:et and the M&E ct in October will be used first mined Riccall, Whitemoor as• the Contractor: M TWO Calor Gas Cementation 1994 were station and North Selby. underground Geology petroleum Ltd installation JLE SUPP Each would have liquefied gas (LPG) • Consult among s. a the UK. pair of shafts for The geology LEM ing Enginee storage transport

SITE VISIT REPORT:

UK F

1994 Rail Link in October the Heathrow Express prosecution excavations on world. The criminal of the NATM station UK and across the the works and CASE STUDY: Collapse s for the tunnelling industry in the later, after working on to recover during ramification ns made engineer four years had high impact shields and its design-buildnce of how decisio aders in the experie trial of the contractor to injury. insult a salient added that the roadhe than anticipated the project, uct was complete predicted aqued The more water Carsington for the project drill+blast. rock and 10.5km long ts mining or ctors bidding right when harder The hand amoun a Contra to turn ded CASE STUDY: seriously wrong. keep large and 1996 provi as. They were JUNE aders go ssed air to Its REPORT: roadhe in 1998, under compre cts. before Christm their es SITEtoVISIT design can upservic edproje giverail on the hillside advancre c was four drives would be against publi infrastructu ader shield, out of the ed to hmarks mega forced three dwhich kept its roadhe of future , stand as benc and open face, funding ingplete lems remain l, com . ion and ed prob control nizat under nel Tunne orga water document ofning, The Chan its well 1983 ative plan well as STUDY: T: MARCH CASE el for the innov successes, as VISIT REPOR the project in truction SITEkes.

• Client: BAA role mod mista that occurred on ng cons similar the mind, for the owner: job in the collapse will always focus outstandi s will avoid • Consulting Engineer hatever jinxed the well October 1994 achieved be to other h appears remains if it is being Mott MacDonald whic beginning, all of the question then? The

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