TunnelTalk Special Edition: USA Focus and Case Studies

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SPECIAL EDITION FOCUS: USA CASE STUDIES

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TUNNELTALK SPECIAL EDITION USA FOCUS AND CASE STUDIES FROM THE EDITOR’S DESK

Underground infrastructure: Charting the roots of today’s reality

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ew underground projects in the USA are being shaped by projects of the past that introduced techniques, equipment, methods and materials from overseas, including Europe and Japan. These imports expanded the possibilities and forged an industry eager to apply state-of-the-art methods to build much-needed transportation and water management infrastructure. The start of underground lines for LRT and metro systems across the country, as well as highway projects to improve connectivity, and the call for intense CSO abatement projects in the 1980s, 1990s and early 2000s, created the breeding grounds that fostered a burgeoning USA tunneling industry and its transformation from traditional to more advanced technologies.

As a reporter for the international tunneling industry during those years, I visited most of the principle USA underground infrastructure projects of the era, interviewing senior managers of the owners, the consulting engineers, the contractors, and the suppliers. A look back at the articles published during that time highlights: • the achievements of Robbins TBMs across the country; • the application of Lovat TBMs for water networks; • arrival of the first TBMs from Japan and Germany; • the introduction of NATM or the sequential excavation method to metro and highway projects; • the import of steel-fiber reinforcement for shotcrete, segments and in-situ linings; • improved TBM bearing and tailseal greases; • purposed-designed EPBM conditioners; and • high specification hydrophilic and EPDM sealing gaskets for one-pass precast concrete segmental linings.

was a focus of the reporting. What was it that drove a project from a figment of imaginings to the start of planning, in to phases of preliminary and detailed design, and on to either contract bidding and award for construction, or cancelation and disappointing delay of the needed infrastructure. This first USA Special Edition includes a selection of case studies that review this fundamental aspect of the industry together with discussions about the cost of underground projects, their management and the influence of the knowable and unknowable risks involved.

For construction, the means and methods of the case studies indicate how far equipment, technologies and applications have come over the decades, but some might say perhaps not far enough. Costs of projects nowadays have ballooned out of perception and the progress of underground projects seems to be slower today than years ago. How much, for example, is $7-17-27 billion really as a project estimate, and what are the cost centers that add up to those amounts? Review of contract award values indicate that the actual cost of construction is often a fraction of that amount, where in the past it was nearly all. For progress rates, record advances for open-face and TBM headings of today are largely as they were then, and the overall program for projects of similar scale today are lengthening not contracting. Understanding why that should be so are the questions the industry needs to be asking. Investigation of these topics begins now. n

Through all, the genesis of projects and their development through the politics of City, State and Federal Governments,

Shani Wallis, Executive Editor

CONTENTS NEWS

TRIBUTES

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36 Remembering USA industry leaders

The latest from USA planned and progressing projects

METRO CASE STUDIES

WASTEWATER CASE STUDIES

7 9 14 19

37 42 47 54

Seattle LRT system starts with bus tunnels Cautious going at Beacon Hill Undermining the Minneapolis/St Paul Airport Dallas Cityplace LRT planning and execution

HIGHWAY CASE STUDIES 26 Combined road and rail access for Whittier, Alaska 30 Cumberland Gap advances NATM in the USA 34 The Dallas highway congestion solution that got away

Direct by Design

Boston Harbor sparkles in wake of TBMs Milwaukee builds-in a spring clean San Diego ocean outfall and feeder sewer Atlanta takes control of its CSOs: Chattahoochee, Nancy Creek, West Area projects 64 Atlanta’s Mayor: A politician with a vision

ACCOLADES 66 Industry leaders recognized by their peers Copyright© TunnelTalk 2022. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic or otherwise, without the prior permission of the copyright owner. All views expressed in this journal are those of the respective contributors and are not necessarily the opinions of the publisher, neither do the publishers endorse any of the claims made in the articles or the advertisements.

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News Underground award for BART to San Jose

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xcavation of the BART extension under San Jose is set to start in early 2024 following award of the tunnel and trackwork package to the Kiewit Shea Traylor (KST) JV. In a positive sign of momentum and progress for Phase II of the Bay Area Rapid Transit Silicon Valley extension, the Valley Transit Authority (VTA) Board of Directors voted unanimously in early May 2022 to award the CP2 tunneling and trackwork package to KST. The work is awarded on a Progressive Design Build procurement basis and at a bid price of $235 million. The JV edged out its two short listed rivals: the B2TP JV of Acciona, FCC, Lane Construction (a subsidiary of Webuild) with Hatch Associates; and the Bay Valley Connect JV of Bouygues and Vinci with Barnard Construction and consultant Parsons. KST will be assisted in its design engineering by Kiewit Engineering Group and Arup.

Under its contract, KST will excavate 5 miles (8km) of underground route beneath the city of San Jose to link three underground stations. Developed by a Program Management Team headed

by HNTB, the underground alignment is the majority part of the 6-mile (10km) extension that includes a surface

transition from the current end of the line at Berryessa to the east and another transition to the at-grade Santa Clara Station and maintenance yard to the west (Fig 2). Three other major contracts to be let are for excavation of the three underground stations, construction of the at-grade Santa Clara Station and maintenance yard, and procurement and installation of the system-wide services.

After much study and analysis, the underground alignment is currently based on a single large diameter TBM bored tunnel of about 43ft (13m) i.d. that will accommodate both tracks and stacked platforms at underground stations that are accessed from off-street station halls and underground access concourses (Fig 2).

In awarding the contract, the Board also approved a request to review previously completed assessments comparing single and twin-bore tunnel methodologies, in parallel with the initial contract progress.

Avoiding construction disruption as much as is possible is the promise by VTA to the citizens and businesses of downtown San Jose.

Under the Progressive Design Build contract, Stage 1 will include the JV working with the Program Management Team to investigate bored

TunnelTalk reporting

June 2022

tunneling innovations, engineering and design; development of open book cost estimates; and assessments for the work schedule. These activities are anticipated to progress to about December 2023 when Stage 2 major construction can begin.

Led by HNTB, the Program Management Team includes WSP, and General Engineering Consultant MMW, a JV of Mott MacDonald and PGH Wong Engineering. Current estimate for the completed 6-mile extension is estimated at about $6 billion. Completing the project after many years of discussion will provide a one-seat rapid train ride linking San Francisco with San Jose along the east side of San Francisco Bay and into Santa Clara County (Fig 1). n

TunnelTalk references • • • • •

Shortlist for BART to San Jose extension - May 2021 Rethink of the BART to San Jose configuration – May 2020 Funding and single-bore secured for BART to San Jose – May 2018 Single bore option for BART to San Jose – June 2017 A slow road for BART to San Jose – May 2007

Left: Fig 1. The project will bring BART services from San Francisco into Santa Clara Country; Right: Fig 2. Several configurations have been studied to avoid open-cut disruption through downtown San Jose

Los Angeles Metro Sepulveda connection

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s work progresses on the three current contracts of the Westside Purple Line of the Los Angeles Metro, and the Regional Connector in downtown LA and the link to LAX international airport are in final phases ahead of opening, planning continues to take the service through the Santa Monica Mountains into San Fernando Valley via the Sepulveda Pass.

In March 2021, Bechtel as leader of the Sepulveda Transit Corridor Partners was awarded a $69.9 million contract to develop its proposed $10.8 billion heavy rail concept of which more than 60% is aligned underground.

LA SkyRail Express was awarded a $63.6 million contract to further develop its $6.1 billion proposed monorail

TunnelTalk reporting

June 2022

concept that would be an aerial alignment running primarily within the I-405 Freeway right-of-way between the Valley and Westside.

The project is part funded by a local Measure M ballot initiative to raise taxes and invest about $5.7 billion in the San Fernando-Westside link to open by 2033-35. Another $3.8 billion is allocated to extend that service from Westside to LAX by the late 2050s. n

TunnelTalk references • •

All set for mega metro investment in Los Angeles - July 2014 First TBM launch on LA metro extensions - March 2016

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News TBMs prepare for Chesapeake Bay highway drives

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wo mega TBMs of near 13m and 14m diameter are preparing for excavation to double the capacities of the undersea highway links across Chesapeake Bay at Thimble Shoals and Hampton Roads. The two Herrenknecht TBMs procured by the two JVs headed both by Dragados will excavate drives of about 2km each to double the existing immersed tube links built in the 1960s and 1970s respectively.

At Thimble Shoals, the Dragados/ Schiavone JV procured a 12.8m diameter EPBM from Herrenknecht for the single-tube, two-lane subaqueous drive. The JV, with consulting engineer Mott MacDonald, was awarded the design-build project in mid-2016 after submitting a $755 million TBM alternative for the 5,710ft (1,740m) drive.

At Hampton Roads, the JV of Dragados-Vinci-Flatiron-Dodin Campenon Bernard took delivery of its 13.9m VDM (variable density machine) to complete twin TBM drives of 7,500ft (2.2km) long to add four new lanes to the existing four lanes in two immersed tube crossings.

Under its fixed price contract of $3.3 billion for the Virginia Department of Transportation (VDOT) the JV, with design partners HDR Engineering and Mott MacDonald, has also committed to a fixed completion date of November 2025 for the $3.3-3.8 billion project.

For both contracts, the tunnels will be lined with rings of precast concrete segments reinforced with Dramix steel fiber supplied by Bekaert, and fitted with high performance gaskets supplied

by Sealable, (previously Datwyler and earlier Phoenix). The TBMs will advance from enlarged islands at the

TunnelTalk references The 12.8m EPBM and the 13.9m VDM for the Chesapeake Bay highway crossings

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allas Area Rapid Transit or DART is into the planning and preliminary design of a second light rail line through downtown Dallas. The D2 Subway project, with a budget of $1.7 billion, includes 1.3 miles of alignment below grade and three underground stations. The project team, led by DART, includes the City of Dallas, the North Central Texas Council of Governments (NCTCOG), and the Texas Department of Transportation. The only existing underground element on the Dallas Subway is the Cityplace Station and its running tunnels built in the 1990s (see page 19). n

California mega-water delivery project

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nown previously as the California WaterFix, the Delta Conveyance Project for the State Department of Water Resources (DWR) to secure reliable water supply from the abundant north to the dry, high-demand south, has undergone several revisions. Originally based on twin large diameter, long distance TBM drives, the project is currently being redesigned to a single tunnel option. A draft environmental impact report for the revised project is expected in 2022. n

TunnelTalk references •

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June 2022

transitions between the trestle bridges into the existing immersed tube tunnels.

Segments and supplies will be transported by barge to the island job sites and muck will be barged away to licensed disposal sites. TBM excavation was selected for the parallel tunnels to limit disruption of the shipping channels under which they pass and to avoid impact on the existing immersed tubes. These must remain in operation throughout construction of the new links.

TBM excavation at Thimble Shoals was scheduled to start in late 2017 and take about five years to complete, but the schedule has slipped considerably for the JV due to permitting issues, termination of a key subcontractor, and design amendments of the marineworks. For the moment, the TBM remains in Germany at the Herrenknecht factory in Schwanau. Delivery to site is expected in the Fall 2022.

The TBM at Hampton Roads is assembled and ready to start its first of two drives. In the same way as the Herrenknecht TBM that excavated the undersea road tunnel under the port of Miami in the 2000s, the Hampton Roads TBM will take a u-turn at the end of the first drive to return on the parallel drive to the main working site. The slurry mucking circuit of the VDM will make the u-turn with the TBM and segments and supplies will use the first tube to access the second drive. n

Dallas D2 Subway heads under downtown

•

TunnelTalk reporting

WaterFix construction preparations and sequences September 2017 VIDEO: California Bay Delta tunnel project – November 2015

• • •

Thimble Shoals award - July 2016 Hampton Roads award - March 2019 Excavation wraps up on Miami Port link - May 2013

Sound Transit extensions for Seattle LRT

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ound Transit is planning new extensions of its Link Light Rail system in Seattle. These include: • The West Seattle to Downtown route, which includes 4.7 miles of LRT service and four stations with a potential underground section and station, and • The Ballard to Downtown line with 7.1 miles of new service and a new downtown Seattle rail-only tunnel.

Sound Transit has approved preferred alignments and other alternatives are to be studied in a draft environmental impact statement which is currently progressing. The underground network of Seattle LRT services began in the 1980s (see page 7) with excavation of the city bus tunnels. n

Washington DC Potomac River CSO project

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fter the Blue Plains, Annacostia and Northeast Boundary tunnel contracts for its Clean Rivers Project, DC Water is pressing ahead with the last in its consent-decree driven CSO control program for the Washington DC area. The final 5 mile x 18ft i.d. (8km x 5.5m) tunnel will intercept the last polluting CSOs along the Potomac River and convey all flow to the Blue Plains wastewater treatment plant. Contract award and start of construction is anticipated in mid-2023, with operations beginning by the March 2030 consent decree deadline. n

TunnelTalk references •

Potomac River CSO approved in Washington DC - April 2020

Seattle LRT system

starts with bus tunnels

CASE STUDY: An extensive light rail network in Seattle began in the late 1980s with excavation of the Seattle downtown bus tunnels. Today the tunnels accommodate both metro trains and electric bus services and mark the beginning of several underground extensions of the LRT system for Sound Transit, including the deep Beacon Hill underground station on the extension south to Tukwila; TBM drives for the U-Link and North-Link extensions; and the EastLink services that share space with highway traffic through the famous Mount Baker Ridge tunnel and run under the streets of Bellevue in the Line’s new SEM tunnel. For Sound Transit LRT, it all started with the Seattle bus tunnels.

SITE VISIT REPORT: DECEMBER 1987

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new underground street for buses only was Seattle’s answer to urban traffic congestion.

Parallel 1.3 mile (2km) long tunnels, up to 45ft under the streets of the central district, will take up to 50% of the buses off the streets and increase the present 4 mile/hr commuter traffic flows to about 12 mile/hr in peak periods.

Tunneling began in November 1986 when the Guy F Atkinson/Dillingham JV won the contract with the lowest of eight competing bids at $44.2 million, well below the $61.6 million Engineer’s Estimate. Instead of the more usual 30-to-36 month construction period for a job of this scale, Seattle Metro, the client, imposed a tight 17 month program to have the system in service by early 1990. To meet this, Atkinson needed two reliable machines, one for each tube, designed, built and delivered quickly.

The geology is mostly over-consolidated sands, silt and clay with the water table rising close to the surface south of Pioneer Square Station (Fig 1). North of the Station, the water table is well below the tunnel elevation and the dry over consolidated materials can be very hard.

“Ideally, a closed, pressurized tunneling shield would be better in the water bearing ground south of Pioneer Station,” said John MacDonald, Project Manager for Atkinson, “but there are deep tie backs anchoring the many sky scrapers along the tunnel route and to deal with these we need easy access to the face. Also, as the majority of the tunnel is in dry, competent ground, we chose two open-faced machines with breasting plates to hold the upper part of the face in softer wet conditions.”

Of the various machine proposals, the one from Robbins was “technically superior and most economical.” Robbins is also Seattle-based making delivery easy and quick.

The machines are quite different from the more familiar open-faced shields. To provide optimum face access, the backhoe paddle-type excavator is mounted on a tripod of inter-reacting hydraulic cylinders. Robbins has built two other machines to this design, one used on the Washington DC Metro in 1974 and the other used on the Caracas Metro in 1978.

The 21ft (6.4m) diameter, 140 tonne, 600hp shields have a thrust capacity of 2,400 tonne via the 20 thrust rams 7

From left: Concrete segments are replaced by ribs and lagging in the station areas to facilitate station box excavation; One of the two 6.4m diameter Robbins tunneling shields with its unusual tripod excavator mounting

acting against the precast concrete segmental lining. The 120hp paddle excavator does not have very powerful breakout which could be a problem in the harder ground of the northern section, but the ground was not considered hard enough for the more expensive roadheader-type excavator boom.

Both machines were launched from the southern portals established in a back­filled area behind a heavy retaining wall built in a vacant lot near the railway station. While it is the most convenient place to start, it is also the most difficult.

Not only is it in the worst ground conditions, although the water table has been lowered to 15ft below the surface, but also the machines begin immediately on a steep 5.5% down gradient and on a 150m radius curve to pass under an active railway tunnel about 800ft from the portals. With only 4.5ft between the two, the ground was strengthened by jet grouting to 7ft below the bus tunnel invert. This was done from within the 80-year-old, concrete-lined, doubletrack tunnel without interrupting traffic.

There is a second tight 85m radius curve as the twin tunnels turn into Westlake Station. To negotiate these tight horizontal and vertical curves, the 20ft long shields are articulated between the forward shield and the main body and again between the main body and the tail skin.

The shields are also equipped with computer guidance systems from ZED Instruments.

Two linings are better than one

Originally, the Parsons Brinckerhoff Quade & Douglas design included a 20cm thick, one-pass, bolted concrete segmental lining. “Being the permanent lining, these segments would have to have been erected with great accuracy which would have been extremely difficult and time consuming particularly at the start of the job with a new crew, new machines, in wet ground and on the spiral curve,” explained MacDonald.

An added concern was the lack of an experienced tunnel segment supplier in Seattle to make what would have to be heavily reinforced bolted segments with a watertight gasket and cast to within 1/64th of an inch tolerances. Good quality annular grouting would also be essential to keep ground settlement to the 0.25in limit at property lines, which, particularly in the poorer ground of the southern section, could not be guaranteed.

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“We therefore submitted and had accepted a value engineering proposal (VEP) alternative of erecting a 15cm thick, lightly reinforced, concrete segmental primary lining and finishing with a 30cm thick unreinforced in-situ concrete final lining,” said MacDonald. A continuous PVC membrane, 1.5mm thick in the arch and 2mm thick in the invert, between the primary and secondary lining, will render the tubes watertight although this may be omitted in the drier conditions north of Pioneer Square Station.

The concrete segments being used are the first tunnel segments ever cast by the local supplier Tacoma Concrete Technology and there is no annular grouting at all. As each ring of eight 1.2m wide segments leaves the tail skin, it is expanded by small jacks at the spring line joints and fixed with wooden wedges. Settlement is further controlled by removing the teeth that protruded beyond the cutting edge thus avoiding a 9mm overcut.

While effective, this jacking expansion method does not produce a uniform lining and several of the segments are cracked and out of alignment particularly in the soft ground areas. This is of temporary concern however, since the final lining will correct this together with any variations in line and level to within the 3in tolerance.

Although a two-stage operation, the VEP saved $1 million and no extra time was requested. “We are much happier with this method and feel the owner will end up with a better product,” said MacDonald.

During the site visit, both machines were in the 365m long Pioneer Square Station area. Unfortunately, the 175m long cut-and-cover excavation had not yet been carried out and the machines were having to drive through the area erecting temporary ribs-and­-lagging support. The machines are not designed to erect this type of lining and it was slow, heavy manual work. The concrete segmental lining was replaced by ribs and lagging in this area in order to make subsequent break-up and box excavation easier. Excavation would have a more significant effect on a segmental lining and it would be more difficult to control the dismantling of the tunnel with an eighth of the lining being removed with each segment.

Four cross passages excavated by hand will also have ribs and lagging as primary support.

When on site, progress was said to be satisfactory although there had been some problems with the machines. High stresses in the six hydraulic cylinders which make up the

tripod excavator mount caused repeated failures particularly in the upper set which take most of the force of the downward action of the excavator. It took some time to correct this.

The circular segment erector ring was a problem initially.

The flex and slight squat of the shield under high steering load conditions often made the rotation of the ring difficult.

This was corrected by adding rollers between the shield hub and the rotating ring.

The ground on the whole was behaving well. There were few boulders and the sands stood well enough to leave traces of the excavator teeth, but crumbled when broken into. Although the geology is well known, Shannon & Wilson completed a thorough site investigation and some strata have proved harder than predicted, particularly the compacted silts which caused overstressing of the tripod excavator hydraulic cylinders. With the softer wet ground now behind them, the breasting plates are rarely required except as a precaution when standing still.

Progress on average is 30ft/24hr day, five days/week with a best advance of 96ft in three 8hr shifts when erecting segments. The shield’s central belt conveyor transports the muck up and over to the waiting 10m3 rail-mounted skips pulled by diesel locos. Once on the surface muck is trucked to a landfill site 20 miles away.

Tunneling is expected to be finished early in January 1988 when the machines are due to break through into the Westlake Station box. This station and the gradual rise to the Convention Centre Station on the surface are

being completed as a separate cut-and-cover contract

by SCI of Canada.

Providing the finishing touch

A five-month concreting program will then start using 192ft (58.5m) long forms supplied by Custom Forms of Kansas.

The invert of one tube will be cast first and as work on the invert of the second is in progress, the arch of the first will be cast. A striking period of 16hr will allow one pour/day.

Each 18ft 3in (5.5m) i.d. tube will carry one bus lane, the road deck being formed by backfilling the circular invert with concrete. Both ends of the underground section connect directly with the freeway system and the plan is that buses driven by diesel on the surface will, with the push of a button, convert to electric trolley type buses in the tunnels.

When services begin, scheduled for early 1990, 290 buses/hr carrying up to 18,000 passengers will pass through the tunnels at peak periods. Services will only run between 5am and 7pm, with locked gates barring the tunnel entrances when closed.

Of the $416 million scheme, the underground elements cost $395 million, half of which is funded by the USA Federal Urban Mass Transit Administration with Seattle Metro meeting the rest.

This is however an interim solution since the tunnels are designed to become an integral part of a future more wide­spread light rail network when the need for a more efficient system arises. n

Cautious going at Beacon Hill SITE VISIT REPORT: DECEMBER 2006

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careful, controlled approach to excavation of the Beacon Hill metro station in Seattle interrupted TBM excavation of the running tunnels. After completing the first of four drives in July, the contractor’s EPB TBM stood still waiting for finish of SEM excavation of the station’s 132m long southbound platform tunnel. This would allow the machine to pull through and resume excavation of the south bound running tunnel by mid-December.

Suggestion to mine through the station and break up the 6.4m o.d. TBM tunnel to create the 11.13m wide x 9.72m high (86m2) platform tunnel was said to have been considered but rejected on concerns about the stability of the glacial deposits at station level and the ability to work safely and effectively in the confined spaces around of the segmental lining.

“We dismissed the idea back in the design stages,” said Dick Sage, the project’s Deputy Construction Manager for Sound Transit. “It was suggested again by Obayashi after award of contract” but for various reasons the alternative was again rejected. On previous projects in the USA where pre-excavated running tunnels have been broken up into metro stations, most recently by Obayashi in Minneapolis for example (see page 14), the stations were of a different configuration, in harder, more stable ground conditions, or were through shallower open-cut station excavations, explained Sage.

That the TBM reached the station before it was ready for a pull-through at Beacon Hill is a combination of slower than anticipated SEM work and better than expected performance by the Mitsubishi EPBM. The TBM program 9

TBM assembly on the MSE platform before being walked in under the elevated 1-5 freeway to the west portal headwall

anticipated a rate of 50ft/day working three 8h shifts/day.

On its first run the TBM and its crews achieved 25-35ft in the one 8h shift/day, bringing it to the station headwall well ahead of station pull-through readiness.

The Mitsubishi EPBM ordered by Obayashi Corporation for its Central Link LRT contract arrived on site in August 2005 and was assembled on a ramp of mechanically stabilized earth to provide an assembly and launch pad for the TBM at the west portal headwall. The earth ramp is an extension of a viaduct that carries then LRT line from grade to the west portal. The viaduct would not

have supported assembly of the TBM and its back-up.

“Early arrival of the TBM at the station works is also the result of an owner-controlled float of one month on the TBM schedule,” explained Sage. “This was built into the schedule to allow time to deal with anticipated boulders in the glacial geology and to prevent the TBM work becoming the contract’s critical path. The SEM station was the evident critical path element and we wanted it to stay that way.”

Even though the TBM is delayed resuming its first running tunnel drive, it does not affect the overall contract

Beacon Hill station started with a test shaft

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xcavation of the Beacon Hill underground station started with a test shaft. At about mid-point along the 1-mile long twin tube running tunnels, the station lies beneath an overburden of about 170ft that comprises alternate layers of water bearing sands, wet silts, and layers of impermeable clay and tills. With TBMs used to excavate the running tunnels, NATM or the sequential excavation method (SEM) is selected for design and excavation of the station shafts and its complex junctions, cross sections and structures with dewatering to support station excavation.

The test shaft is designed to explore: • the boundaries of the strata • the character of the ground water • the response of the different materials to dewatering, grout injection and other pre-support techniques; • the potential for ground movements to test different construction and support techniques.

The proposed 18ft o.d. test shaft will be excavated within the envelope of the 56ft o.d. x 170ft deep main access shaft (Fig 1). It will be set off-center and will incorporate three short test adits within the diameter of the permanent shaft and located at three different levels.

One will explore the water-bearing sands, another a layer of silt, and the third will be excavated in the highly slicken-sided clay. The applicability of the barrel vault method, a tunnel crown pre-support method proposed for the sand and silt layers, will be tested on a smaller scale during the test shaft program.

Test results were used to finalize station design and prepare contract documents for design-bid-build procurement of the station and the running tunnels.

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Fig 1. Original design of the deep mined station

Design was completed to 100% by section designers Hatch Mott MacDonald/Sverdrup JV and their specialist NATM/SEM subconsultant DSC, the Dr G Sauer Corporation (now Dr Sauer & Partners).

Four contractors pre-qualified for the test shaft contract Kiewit, Atkinson, Traylor Bros. and Coluccio Construction Co – and in early 2003 the $2 million contract was awarded to Coluccio Construction as the lowest of the bids. During its contract, Coluccio struggled with ground conditions, the application of NATM as a construction concept, and with the advance of the works as a test process that required close control and monitoring by the designers and teams of contract supervisors. While at one point the test effort was almost cancelled, works continued and NATM/SEM was confirmed as applicable for excavation of the deep, station complex.

schedule, according to Joe Gildner, Deputy Director for Technical Services at Sound Transit. Behind schedule SEM excavation of the station also does not affect overall project completion. “We have another ownercontrolled float of six months on the project-wide South Link construction program and while we have used up four of them, we are 60% through construction and still anticipating on-time opening of the initial 23km segment from downtown Seattle to Tukwila in Summer 2009, and the link to Sea-Tac Airport in December 2009.”

Advancing SEM excavation of the deep level station has deliberately followed a tightly controlled program that combines daily decision-making meetings by representatives of the owner (Sound Transit), its construction manager (Parsons Brinckerhoff), the design-bid-build engineers (the Hatch Mott MacDonald/ Jacobs Civil JV), the NATM construction design support specialists (DSC, the Dr Sauer Corporation), and Obayashi Corp which contracted the US division of Beton und-Monierbau to provide NATM/SEM assistance to its construction crews. In addition, Shannon & Wilson is on site as Sound Transit’s geotechnical instrumentation monitoring consultant. Construction Management is with Parsons Brinckerhoff Quade & Douglas with Babendererde Ingenieure as TBM specialist and ILF as SEM subconsultant to Project Engineers, the Parsons Brinckerhoff Quade & Douglas/Earth Tech/URS JV. Since award of contract in mid-2004, and start of the station excavation in early 2005, several design and construction method changes have occurred to reduce risk and facilitate safe excavation operations.

An initial change, following a trial shaft contract completed in 2003, converted the station’s two 55m deep shafts from a NATM approach to full depth diaphragm wall construction. A supplemental program of site investigation drillings then initiated a comprehensive program of jet grouting to consolidate lenses of potential flowing sands, and a dewatering system to reduce hydrostatic pressures in permeable soils below the water table.

In addition, the whole station design was shifted to the west into more favorable geology and into the zone of pre-consolidated ground. Ventilation dampers were also taken from enlarged cross passages and incorporated into extended lengths of the main platform tunnels to eliminate these challenging excavations (Figs 1 and 2).

“These design changes reduced the project’s risk levels considerably,” said Sage. “We are about 60% through the contract (about 70% through SEM station excavation) and about 65% through the contingency fund allocated to the contract. Some $7.5 million of this was spent on the jet grouting and dewatering programs that have proven very cost-effective risk-management investments.”

Once into station cavern excavation, the flexibility offered by the NATM method has allowed changes by the round if necessary, to deal with conditions as encountered and to improve productivity. As well as the specified elements of systematic support, the contract includes a toolbox list of items that can be used as conditions require. These include rebar spiles, grouted pipe spiles, metal sheets, provision of a face wedge, pocket excavation, face bolts, permeation and fracture grouting, soil nails, additional reinforced shotcrete, and horizontal vacuum dewatering. All have been used at some stage of the excavations to date.

Station excavation is designed to progress on 4ft (about 1.2m) rounds of top-heading, bench, and invert, with the large 14m wide x 12.5m high, 1,500ft2 or 140m2 concourse cross adits divided into twin side wall drifts and the smaller 11.13m wide x 9.72m high, 930ft2 or 86m2 platform tunnels split by a single side wall drift.

Above: Fig 2. Isometric of the redesigned layout of the station Below: Breakout of the main access shaft into the ventilation adit ahead of SEM/NATM excavation of the station complex

Specified primary support of each round comprises 5cm of dry mix, steel fiber reinforced shotcrete, a lattice girder installed at 1.2m centers, and two layers of wet mix shotcrete reinforced with two layers of welded wire mesh for a total thickness of 35cm. To meet the specifications, Obayashi started the job using hand-held shotcreting nozzles for both the specified steel fiber reinforced dry-mix flashcrete and the wet mix secondary layers. Both wet and dry shotcrete was pumped from surface batching units and nozzlemen work in manbaskets for the higher faces.

Mobilization and progress for this complex NATM operation however has not been easy. Training and keeping workers has been difficult and emphasizing the importance of the detail of the work has been an ongoing focus of supervision. Nevertheless, Sound Transit confirmed that “the quality of work achieved to date has been very good” and “excellent”.

Excavation of the station advanced from the station’s 49m deep main passenger-elevator access shaft into the large section concourse cross adit, then in both directions along the southbound platform tunnel (uncovering the waiting TBM at the station’s west headwall) and subsequently in both directions of the northbound platform tunnel.

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SEM/NATM excavation of the large 140m2 concourse adit from the main access shaft (left) and of the 86m2 platform tunnels (right)

From the main access shaft, excavation of the 20m long concourse adits to the platform tunnels was preceded by installation of a full length barrel vault pre-support comprising rows of 23m long perforated steel pipes installed above the crown and extending to the platform tunnel headwalls. The self-drilling pipes were then grouted with microfine cement to refusal criteria. In the more favorable conditions of the south adit, the two rows of the barrel vault used for the north adit was reduced to one.

At Obayashi’s request, the center drift top heading was increased in cross section to permit use of a Liebherr 900 excavator. This center drift top heading was then driven all the way through to the headwall of the lateral platform tunnels before the bench and invert excavation closed the circle.

As excavation advanced and headings opened up, Obayashi increased its initial aggressive baseline schedule of working a single crew on each of three 8h shifts/day to using two crews on alternate headings/ shift, 6 days/week. As more space became available, the shotcrete pumps were relocated underground closer to the faces, which minimized blockages and improved productivity.

After a steep learning curve, that included frequent turnover of workers, cycle times came down substantially from more than 45hr/round initially and a steady fall from

about 15hr/round to about 6hr/1.2-1.4m round. This equals about 6m of platform tunnel completed/week of 24hr/day, 6 days/week.

To improve productivity further, Obayashi applied in early 2006 to replace the wire mesh with steel fiber shotcrete reinforcement in the secondary wet mix layers. After some difficulties with fiber dosage control and blocked lines, the change was accepted, once a second 76m3/hr weigh batcher was introduced specifically for batching wet-mix shotcrete. A smaller 46m3/hr volume batcher replaced initial supply of pre-bagged dry-mix shotcrete.

A small Oruga mobile shotcrete robot was introduction for the proposed switch to wet-mix steel fiber-reinforced shotcrete, working still with hand-held nozzles and manbaskets. A smoothing layer of shotcrete will be applied to even out any irregularities and cover steel fibers before application of the station’s PVC waterproofing membrane and its final cast in place concrete lining.

“Ground conditions as experienced in the station have been better than anticipated,” said Sage. “Excavation in the beneficial jet-grouted sands has been faster than in the clays. There are geotechnical instruments to the n’th degree monitoring the work. Maximum recorded surface settlement to date has been about 6mm with maximum crown deformation in the excavations recorded at 15mm in a large concourse adit heading.”

TunnelTalk references

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Beacon Hill opening celebrations – July 2009

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Owner’s approach to Seattle’s U-Link extension – July 2010

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Mobilization of Seattle’s U-Link extension – July 2010

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Seattle selects East Link route - August 2011

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Months early for U-220 TBMs in Seattle – August 2012

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Seattle pushes on with LRT extensions – August 2012

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VIDEO: Seattle Northgate Link TBM dedication – April 2014

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VIDEO: Breakthrough on Northgate Link – July 2015

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Final breakthrough for Northgate LRT – September 2016

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VIDEO: SEM excavation for Seattle East Link LRT – May 2017

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Future of Seattle LRT developments – February 2021

With the southbound platform tunnel complete and the TBM ready to relaunch on the last half of the southbound running tunnel, station excavation is concentrated on the northbound platform tunnel.

This is programmed to be fully excavated and lined in the invert well ahead of arrival of the TBM in about June 2007 on its parallel running tunnel drive. Total duration of all the NATM/SEM excavation for the station is scheduled to be 24 months of the total 48-month contract with application of the waterproofing system and the in-situ concrete final lining to follow.

The PVC waterproofing membrane is a full, hydrostatically sealed liner that passes under the rebar reinforced concrete invert slabs and behind the steel-fiber reinforced in-situ concrete of the arches. “The PVC membrane design incorporates regular waterstops to isolate areas of waterproofing

vital to the overall network of public transport and the plan is to run a joint LRT/ electric bus operation for this section of the line. “We are working with King Country Metro, operator of the bus tunnels, to incorporate our LRT rolling stock and run an integrated schedule with new hybrid buses being prototype tested at present,” said Gildner. The bus tunnels will be closed for two years to complete the retro-fit.

Cast steel-fiber concrete will finish the fully waterproofed lining

to ensure more effective remedial work should any leaks appear with time,” explained Sage, during a return site visit in late July 2007. “The steel fiber reinforced concrete arch, designed by Hatch Mott MacDonald, prevents rebar installation damage of the PVC and saves time on the construction program.”

Obayashi is using a 40ft long form from Everest of Ontario, Canada, to cast the 14in thick arch lining in the 32ft wide x 30ft high o.d. station platform tunnels. “The steel-fiber concrete saves us two days as well as steel-fixing crews on the original rebar reinforcement alternative,” said a shift manager for Obayashi. Ready mixed concrete with 50lb/yd3 of fiber is dropped into Schwing pumps at the bottom of the working shaft and pumped a maximum 300ft to the forms. Each 40ft long, 170yd3 pour takes about 6hr to complete.

The capital cost of the initial 14-mile Sound Link segment with its 11 stations is estimated at some $2.1 billion in year-of-expenditure dollars. This will be funded principally via a sales tax levy adopted by taxpayers in 1996 and through a requested $500 million grant from the Federal Transit Administration (FTA). In May 2002 the FTA issued its Record of Decision (ROD) approving the project’s environmental impact statements and $91 million of the grant was released. Allocation of the remaining $409 million is anticipated in Spring 2003 after a further full review by the FTA, a 60 day review by Congress, and another review by the Inspector General with the Department of Transportation. Services on the completed initial operating segment are scheduled to start in 2009 with a bus shuttle conveying passengers to SEATAC Airport.

Seattle metro system build out

Meanwhile, Sound Transit is pressing ahead with final design of the 3.15-mile (5km) U-Link to extend the system from downtown north to the University of Washington.

The line is all underground in twin bored tunnels with open-cut underground stations at Capitol Hill and on the University campus. A $35.2 million agreement with the University was reached in June to site the station and progress work on the campus. North Link Transit Partners, a JV of Jacobs Associates, HNTB, Earthtech, and 26 subconsultants, is appointed by Sound Transit to complete final design of two conventional designbid-build contracts for the University Link works.

Construction of the estimated $1.6 billion line is subject to approval of a $750 million Federal funding request to be submitted in November for anticipated approval in Fall 2008. n

Conditions for station excavation were better than anticipated according to Sage. “We did have one incident of ground loss in the arch of a side drift top heading that migrated in a chimney to an upper clay layer and stabilized. There was no depression on the surface.”

Sage added that the quality of SEM work by the contractor, and control of Final breakthrough after averaging 25ft (8m)/day through the glacial till of Seattle surface settlement to 0.8in maximum, compared to the 2.3-2.4in predicted, was excellent.”

In mid-August 2007, the Mitsubishi EPBM was about 400ft (122m) into its third drive and about 1,300ft (396m) from breaking into the completed station platform tunnel. Once pulled through the station cavern, the TBM will complete its fourth and final drive to the east portal. SEM excavation of three cross passages can then begin.

In addition to the Beacon Hill section, work on this initial LRT line will include retro-fit of the Seattle electric bus tunnels. These twin 1.3-mile long tunnels, with five underground stations, were excavated in the late 1980s and were designed to convert in future to mass transit rail services (see page7). The bus services however are 13

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

SITE VISIT REPORT: SEPTEMBER 2002

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BM tunneling and mined station excavation is taking the Twin Cities first light rail transit line beneath the Minneapolis/St Paul Airport.

Excavation runs up to 70ft (21m) beneath the runways, terminals and taxiways of the airport, making use of the area's expansive cap of Platteville Limestone to provide a natural layer of solid support.

During a site visit in July 2002, the first 7,400ft long x 21ft o.d. (2.25km x 6.5m) segmentally lined running tunnel was finished and the Herrenknecht EPBM was some 500ft (152m) into the parallel drive. The Obayashi/Johnson Bros JV had also started excavating the 14-6ft deep topheading of the 525ft long x 60ft wide x 40ft deep (160m x18m x 12m) Lindbergh Station.

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

Top of rail at the center of Lindbergh Station is about 37ft (11.3m) beneath the limestone cap, which is about 30ft (9m) thick, and creates a flat ceiling to the station excavation.

Client for the underground works at the airport is the Metropolitan Airports Commission (MAC) and the design team for the design-bid-build contract is led by HNTB Corporation with specialist subconsultants Hatch Mott MacDonald for tunneling and ventilation; CNA Consulting

The running tunnels of the LRT pass directly beneath the airport and are tracked by a moving exclusion zone as the TBM advanced across the central alluvial valley beneath the taxiways (Fig 1 top right)

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the Minneapolis/St Paul Airport Engineers for mining and geotechnical engineering and Hammel Green and Abrahamson, architects for the Lindbergh station. Obayashi/Johnson Bros won the contract in early 2001, as the second lowest of four bidders, with a bid price of $110 million, after the lowest bid by $500,000, submitted by the Frontier Kemper/LLC JV, was disqualified on a technicality. The other two bids were from the JF Shea/Traylor Bros JV and the Kiewit/ McNally JV. All bids were higher than the Engineer’s Estimate of $76 million with the Obayashi-Johnson JV bid some 30% higher. Extra funds were secured from the Federal Transportation Authority to meet the shortfall.

The project is funded 53% by Federal funds and 47% by State and local funds.

From the transition portals either side of the airport, the otherwise at-grade LRT alignment dips at a 5% gradient into the underground section. Working from the north portal, the tunnels are designed to stay within the dry St Peter Sandstone and under the protection of the limestone cap as far as possible (Fig 3). At two points, however, the cap has been completely eroded by ancient glacial activity. In these valleys the tunnels pass into glacial and alluvial fill deposits under the full influence of the higher ground water table. For this reason, subconsultant Hatch Mott MacDonald specified the use of a dual-mode EPBM, working in the open non-pressurized mode in the dry St Peter Sandstone and converting to the closed pressurized mode through the water bearing alluvial fill.

supplied by Phoenix AG of Germany (now Sealable) via its Phoenix North America division.

"We are not intent on breaking any records here," said Zick, "but the sandstone is favorable, and in the open mode we regularly achieve 20 rings or about 100ft (30m) a day, working three 8hr shifts/day, 5 days/week. We are about one month behind on the TBM program at the moment but expect to make that up on the current drive.”

This is the first large diameter TBM into the USA market for Herrenknecht. During the visit, the operator on duty said that it was a much more sophisticated machine than any he had operated in the past. "You have to be much more technically minded to operate this type of machine but once you know what you are doing, it is easy to control and manage. It has a nice operator's cabin and plenty of clear space in the trailing gear for maneuvering supply trains and feeding segments through the invert to the mechanical erector." The TBM's SLS-T guidance system, is supplied by VMT of Germany.

At all times, in the open and closed mode, the JV is injecting a foam conditioning agent. The dry sandstone has practically no compressive strength but has a 90% quartzite content. When excavated, the non-cemented, weak interlocking material degrades to fine-grained yellow sand, much like beach sand. The foam reduces wear on

From top: Figs 2 and 3. Plan and section of the underground alignment On winning the contract, Obayashi/Johnson directly beneath the airport

Bros confirmed an order for the used 6.5m diameter Herrenknecht EPBM that was first used on the Singapore Metro. The machine was refurbished in Germany and arrived on site in August 2001 for a launch on the first drive in October 2001.

Initially the intention was to use trains of muck cars.

The capacity of each train however, was limited to four-cars or half a ring by the 5% portal gradient on the outbound, fully-loaded journey. "We decided after machine launch to install a conveyor system," explained Paul Zick, Project Manager for the JV. Supplied by Robbins, the 24in wide conveyor travels at 400ft/min and has a discharge capacity of 300 tonne/hr. Rick Gomez of Arizona was engaged to trouble-shoot E&M glitches during launch of the TBM and commissioning of the conveyor system. During the visit, it was explained that reliability of both was very good with up to 75% availability of both systems as an integrated production unit.

The precast segmental lining, designed by Hatch Mott MacDonald, comprises six bolted and gasketed segments and a key in each 1.5m wide ring. Procurement of the segments is subcontracted to Technopref Industries, a subsidiary of Montreal-based Construction Demathieu & Bard (CDB), operating from its County Concrete Corp subcontractor's fabrication yard in Roberts, Wisconsin. The carousel is equipped with 49 moulds supplied

by CBE of France. The production line includes a two-stage steam curing process. Gaskets are

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Excavation of the station cavern topheading with its flat limestone crown

the cutterhead and tools and suppresses dust, while in closed mode it ensures effective EPB extrusion of the loose glacial deposits through the screw's guillotine gate onto the transfer conveyor.

On approaching the two glacial valleys, conversion from open to closed mode was to take place at least 500ft before leaving the protection of the limestone cap. On the first drive, as the TBM approached the first valley, at about mid-point along the drive, this conversion was agreed to be too early, with a rapid drop in progress as the TBM labored in the closed mode in the dry sandstone.

The contractor therefore decided to return to open mode, making the decision for conversion later. Although the design team has a quality assurance inspection role, its representatives do not have supervisory responsibility, explained Dr Saldr Selcuk, Construction Coordinator on site for HNTB. "The contractor is responsible for its own supervision, with the design team providing an advisory service to both client and contractor."

Conversion from open to closed mode is a tricky moment.

The transition from dry sandstone to wet glacial fill is abrupt and difficult to predict. As a result, conversion on the first drive, both at the first valley and the second, were slightly late and ground was lost through over excavation.

Fortunately, this did not cause settlement or disruption to airport operations. The area above the first valley is covered by the 18in thick concrete apron resulting in no evidence of settlement or damage. The over excavated zone was backfilled with grout injection.

Ground losses on the transition to the second valley were more severe and several sinkholes developed in a parking lot. TBM progress was not interrupted and the parking area was restored. In addition, as an added precaution, the airport operated an exclusion zone for airport traffic as the TBM passed the first valley under the runways (Fig 1). The impact of the 100ft wide x 250ft long exclusion zone closed one terminal gate and its taxi routes for a maximum 11 days for each drive.

The first 2.25km drive ended in April 2002, when the TBM broke through into the cut-and-cover transition at the south portal. The 350 tonne TBM was then lifted 45ft, and transported by night back across the airport, to the north portal and lowered 40ft into position for the second drive. This started in June 2002 and was scheduled to finish in October 2002.

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Mined station

Excavation of the Lindbergh Station started in April 2002 with a full width 60ft x 14-16ft high topheading advancing from one of the two ventilation shafts, which were completed as part of an earlier contract. Since mucking out via this shaft was not permitted, excavation had to wait until the TBM was through the station zone and close to finishing its first drive.

A glory hole was then dropped into the crown of the tunnel some 5ft (1.5m) below the topheading invert, for mucking out via the conveyor through the north portal staging site.

The station also lies, almost completely, in the favorable St Peter Sandstone and is being excavated by excavators. A visit into the topheading illustrated the unusual geometry of the excavation designed by local specialist Dr Chuck Nelson of CNA Engineering. Nelson has extensive experience of working in the area and was involved in the design and excavation of the underground library at the University of Minnesota. Similar with the library, Lindbergh Station uses the Platteville Limestone to create a flat roof.

To comply with design, the crews must remove the 2-3ft intervening layer of weak shale, that tends to flake off when exposed, and cut a minimum 2in into the upper limestone. Excavation of the topheading progresses in two halves with a slight leading to trailing face across the 18.2m width. Once excavated, rockbolts are installed in the flat roof.

Initially the 10ft (3m) long grouted and tensioned bolts were inserted on a 5ft x 7ft (1.5m x 2m) pattern. However, as excavation progressed, vertical deformation of the roof in both transverse and longitudinal directions - "much like a plate" said Selcuk - was being detected by the array of installed instruments. This was more than anticipated and the bolting density was increased to a 5ft x 5ft pattern with an additional resin anchored bolt introduced to the middle of the pattern and retrofitted to the excavated area.

Williams hollow core rockbolts are installed immediately behind the excavation. They are torqued to a minimum 750ft/lb to expand the point anchor system and then prestressed to 30 tonne. The prestress is verified routinely on all installed bolts.

Unsupported walls

Excavation of the station cavern within the St Peter Sandstone is designed without any temporary support in the side walls. The weakly cemented sandstone with its low but adequate compressive strength, has good standup

Breakout of the pre-excavated running tunnels and installation of the station’s precast concrete curved sidewall panels

time properties. To optimize stability and provide more favorable stress distribution, the walls of the topheading and bench are excavated on a slightly curved profile that is achieved using a Webster Schaeff roadheader boom mounted on the CAT 318.

The internal finish of the station comprises a system of 10ft wide x 38ft tall x 12in thick precast concrete wall panels erected as part of the bench excavation. These panels also have a 4ft arch curved profile to accommodate the curvature of the excavated walls. After excavating a maximum 67ft (20m) length of the bench, a cycle of five 10ft wide panels is erected on standard cast-in-place footings. Once installed, the 2-4in gap between the top of the precast panels and the cavern's limestone roof will be filled with dry mix shotcrete and the panels will be contact grouted with a light-weight cellular concrete. A similar system of 5ft wide x 28ft foot long x 8in thick precast, prestressed concrete panels provide a finish across the flat crown. A waterproofing membrane behind the panels will direct any seepage from water bearing bedding planes in the limestone to a central sump.

When visiting the project in July 2002, the JV was preparing a fast track alternative whereby the curved walls of the topheading and bench would be supported with rockbolts and perhaps shotcrete, to allow potentially easier and faster installation of wider wall panels as an independent operation.

precast panels of the suspended ceiling over the entire 530ft long x 60ft wide station will be bolted. Once a sequence of four wall panels is in place, the 6in gap between their top edge and the cavern’s flat limestone roof is infilled with shotcrete. An insitu concrete curb is cast at the bottom for toe support and to seal the gap.

The vertical joints between panels are sealed with single component urethane caulking and insulating foam. After overnight curing, a lightweight-foamed grout is pumped into the annular space between the panels to a height of 35ft (10.7m). This first stage grout is given 24-hours to set after which the remaining void behind the panels is filled with normal sanded grout. A third stage neat cement grout, pumped under pressure through holes drilled in the shotcrete above the panels, finishes the installation.

At the time of the visit, topheading excavation had progressed about 230ft along the 524ft long station cavern and the TBM was fast approaching on its second drive. During excavation of each running tunnel in the station zone, the upper half of the precast concrete rings is replaced with bolted liner plates. These will be easier to dismantle during tunnel breakout and bench excavation of the station.

The project's excavation sequence has presented a rare opportunity to study ground behavior, in that the first TBM drive was through before the start of station topheading excavation, while the second TBM drive would pass directly beneath the shallow cover of the already excavated topheading invert. Above the first TBM drive, topheading excavation revealed several

After site observation and review of instrumentation readings, geotechnical design engineer CNA, permitted the exposed distance to be increased to 83ft (25.3m), which allowed a 4-panel (40ft) installation sequence. The panels were cast by TunnelTalk references County Concrete in the same yard as the tunnel • New design TBM tames the Kuala Lumpur karst - January 2014 segments. The wall panels also accommodate installation of the mezzanine access in the • Crossover TBMs bridge the gap for Robbins - March 2015 station cavern to the platforms below.

• Success for first North American Crossover TBM - May 2016 The wall panels have a cast-in haunch about 4ft from the top to which the 5ft wide x 28ft long x 8in thick (1.5m x 8.5m x 203mm)

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Crossover XRE navigates fault zones in Turkey - June 2020

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Flat crown for Eastern Distributor highway in Sydney - February 1999 17

For the ten cross passages of 20-40ft (6-12m) long, Obayashi/Johnson Bros proposed as a value-engineering design change to modify the excavated cross section and reduce the wall thickness of the in-situ concrete lining from 16in to 8.5in (400mm to 200mm). The owner accepted the proposal and realized substantial contract savings.

Impressive scale of the underground station with its flat crown

After breakout, cross passage excavation progressed on a 7ft (2.1m) high topheading advanced in 4-5ft (1.2m-1.5m) rounds, supported with drymix shotcrete, wire mesh and rockbolts.

Excavation of the bench followed 2-3 rounds behind and again supported with dry-mix shotcrete, wire mesh and rockbolts applied to the sidewalls. In-situ concrete provides the final lining on the sidewalls, inverts, and at the tunnel connections with wet-mix shotcrete forming the parabolic crown. Cross passage excavation was completed by late April 2003 and concrete work was to be completed by late May.

peaks or pockets of grout rising from the tunnel's annular grouting operation into the topheading face. In a paper presented at the NAT 2002 conference in Seattle, the authors described how "water moving along irregularly spaced and steeply dipping joints in the sandstone can erode the weak, friable material causing the loosened sand to migrate and develop voids." The sandstone is also vulnerable to the break back phenomenon when excavated. These break back peaks, as well as incidences of TBM over excavation, are also evident as veins and pockets of grout infill.

Known as the Hiawatha Transit Line, as it follows the Hiawatha Highway, the overall cost of the first 11.6 mile (18.5km) long LRT line for Minneapolis/St Paul, is $675.4 million. As part of the client set-up, the underground section at the airport is administered by the Metropolitan Airport Commission (MAC) and incorporated into its $3.5 billion project for airport expansion started in 1996. The advisory role of the HNTB design team on site is said to have fostered favorable relations between all involved and there had been few causes for disagreement.

For the second drive, the questions were, how would the TBM and lining behave when excavating beneath the shallow (1.5m) cover of the topheading and, how would the walls and topheading excavation behave when being so closely undermined? The TBM entered the excavated topheading zone in early August and early reports from site were that all was going well. Predictions of excessive heave or over excavation had failed to materialize and there was also no evidence of high deformation of the topheading walls.

The remainder of the line, running at grade, is being constructed as a design-build contract managed by the Minnesota State Department of Transportation and the Metropolitan Council. Revenue services on the first at-grade section are due to begin in late 2003 with the southern section to the airport and on to the landmark Mall of America shopping and entertainment complex opening by December 2004. Initial hand over of the tunnels for track laying and systems installations is due

by May 2003, with handover of the Lindbergh Station for M&E installations starting in August 2003. n

The next challenge will come with the concurrent breakup of the tunnels and excavation of Breakout of the running tunnels for excavation of the cross passages the 60ft wide x 18-20ft deep station bench, scheduled to start in November 2002.

Progress report

By May 2003, the second 7,400ft (2,255m) long northbound running tunnel of the project was complete and excavation of the running tunnel cross passages, and of the bench in the Lindbergh Station cavern, could begin.

Final hole through of the TBM occurred on 26 October 2002, 60 days faster than the first south bound drive. The drive went well with no unexpected obstacles and after hole through at the south portal, the leased EPBM was prepared for shipping back to Herrenknecht.

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Dallas Cityplace LRT planning and execution

CASE STUDY: The story of the Dallas Cityplace LRT project is a story of complicated city planning, complex funding arrangements and another application of NATM in the USA to provide the least expensive option for an underground LRT station and TBM running tunnels in the favorable Austin Chalk geology.

SITE VISIT REPORT: MAY 1992

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allas began seeing real action on its much-debated light rail public transport system in early March 1992 with groundbreaking on the first two civil contracts for construction of the 20-mile starter system of the eventual 67-mile Dallas Area Rapid Transit (DART) LRT. SA Healy of Chicago started work on its $86.8 million contract for the Cityplace underground station and its associated 3.5 miles of twin tube running tunnels while across town, Hensel-Phelps of Colorado started work on its $18.8 million contract to build the LRT bridge over the Trinity River.

For DART, the Dallas Area Rapid Transit authority, established in 1983 to manage an integrated LRT network, it has been a long, arduous, expensive and often frustrating process to arrive at this point. Budget and scheduling problems, together with complex planning and design issues, have caused high cost and time delays, but according to Jim Martin, Director of Construction Management for DART: “We are excited to have been given the LRT green light at last and are ready to get construction of the starter system rolling and into operation by the scheduled 1996 date.”

Cityplace station and its running tunnels are the only underground sections now involved on a much scaled down version of earlier proposals for the scheme. The original proposal for the 20 mile (32km) starter system ran underground for about 7 miles (11km) in the downtown central business district (CBD) and was estimated at about $1.1 billion. Approval for such an expensive scheme was denied and cheaper alternatives had to be found. The scheme now being built runs substantially at-grade using existing rail right-of-ways and is priced at $828.7 million.

At Cityplace the system has to be underground. There is no acceptable alternative. From the central business district, the route follows the North Central Expressway which passes through Cityplace, a major commercial and residential development comprising two multistorey towers, the second of which is yet to be built. Both have a major impact on the DART LRT plans.

“Proposed reconstruction of North Central Expressway by the Texas State Highway Department, and intense

development throughout the corridor, combined with environmental and neighborhood concerns, greatly complicated the planning and design of the LRT and consequently resulted in significant delay and cost concerns as various options were investigated,” said Bob Zollars, President of Huitt-Zollars, the Dallas-based consulting firm and general facilities consultant to DART for the starter project.

The principal complication is that the Expressway, built in the late 1950s, is to be increased from a four-lane to an eight-lane freeway and is to be depressed in a deep cut for the 4 mile (6.5km) section running from downtown to just beyond the Northwest Highway.

At Cityplace, the planning and future success of the development is influenced significantly by incorporation of an LRT station. Negotiations in 1986 between the developers and DART agreed the provision of an underground station with underground passages leading to both towers, one either side of the Expressway. In return, the Southland Company, owner of Cityplace and parent of the international chain of 7-11 convenience stores, would contribute toward the architectural finish of the station which, with other civil works and ventilation requirements, will cost about $40 million.

Under the original scheme, Cityplace was an estimated $218 million part of the 7-mile CBD underground section.

In 1989, when DART was charged with reducing costs, a suggestion was to run this section on an elevated structure above the median of the depressed Expressway or at grade on the median. These suggestions however were rejected by the State Highway Department and residents along the alignment.

In June 1989, a compromise was reached. The LRT lines would be accommodated in boxes either side of the highway cutting. Being an integral part of the Expressway project, these boxes, with an estimated construction cost of $189 million, were designed by consultants engaged by the Highway Department and their construction was incorporated in the Expressway program.

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As the box design developed, it became apparent that the costs were rapidly escalating due to the incompatibility of the LRT and highway specifications. It also became apparent that the project would be further delayed from one to three years because of a funding shortfall for the highway project.

“In addition to the cost and schedule problems, further complications arose with the box design; such as constructability, ventilation, safety, access, and additional real estate requirements,” said Bo Cung, Design Project Manager for the North Central section for DART. In Spring 1991, the preliminary design, cost estimate and construction schedule report for the box option was presented by the Highway Department to DART’s Board of Directors.

As prepared, the proposal was unacceptable. The cost estimate proved higher than DART’s budget for this section and the proposed completion date was at least three years beyond DART’s schedule. At an estimated cost of $220 million, the box proposal proved even more expensive than the $218 million estimate for the tunnel.

Design process

In 1991, DART’s Engineering and Construction Department with assistance from Huitt-Zollars and other associated consulting engineers prepared preliminary plans for a revised bored tunnel concept. The HuittZollars team, which included Sverdrup Corporation and HOK Architects, began working with the final design consultants for the box option to assimilate existing data. Additional information was provided by Texas Department of Transportation on a drainage tunnel which was currently being bored beneath the freeway.

Ventilation studies for the box option were used as a starting point for design of options for the bored tunnels.

By combining all available information, it was possible to prepare schematic plans which were used for cost estimating purposes. “Since we were using composite information and were only at a 2% design level versus a 50% design level for the box option, our bored tunnel estimate was extremely conservative and included a large contingency fund,” said Zollars. “Still, our studies indicated the bored alternative would be at least $28 million less than the box option.”

Here in Dallas, the tunneled option has proven more cost effective principally because of the favorable nature of the ground and the adoption of the NATM for the station excavation (Fig 1). Early discussions with the Dr Sauer Corporation (DSC) of Herndon, Virginia convinced DART of the applicability and cost effective advantages of using NATM in this particular ground. DSC, with its substantial NATM experience both in the USA and in Europe, has since been appointed as specialist NATM sub-consultant to Huitt-Zollars and to HDR, the detailed final designer for the tunnels and underground station section.

The geology comprises good quality, homogeneous Austin Chalk which is competent and impervious. With an unconfined compressive strength of between 1,5002,000 psi (10-15 MPa), it is readily excavated.

TBMS or roadheaders

Previous tunneling jobs in the area have shown that the chalk has a long self supporting stand-up time and requires very little initial or long term support. Smaller openings will remain exposed and unsupported for many months, suffering finally from weathering of the surface rather than instability problems. Although below the watertable, the chalk at tunnel and station alignment is generally impervious and dry. Very little ground water seepage is expected, except in the shafts and at the portal zones, particularly the south portal, where excavation passes through poorer water-bearing topsoils.

Chosen route of the starter system which runs substantially at grade with an underground section at Cityplace and under the North Central Express highway (inset)

20

The long road to LRT reality

T

alk of a metro system for Dallas has been on going since the mid-1970s.

With a population of about 2 million, the Dallas metroplex is among the largest in the USA without a mass rapid transit rail system. In 1983, the Dallas Area Rapid Transit was created when 58% of voters in Dallas County and 14 neighboring cities voted in favor of regional public transport and agreed a 1% sales tax levy to support such a scheme. By 1986, one more city had elected to join DART. Since then two have withdrawn leaving DART with 14 member cities in which its services will operate. DART is governed by a 25-member board of directors appointed pro-rata by the city councils of each member city for a two-year term.

Once in operation, DART took over the public bus system, its only current operating system, and extended it to the member cities and began work on an integrated transportation strategy. Using Federal cost-effectiveness guidelines approved by the USA Department of Transportation, DART developed a plan which incorporated bus services, high occupancy vehicle (HOV) lanes on freeways, heavy commuter rail and light rail transit and set a target date of 2010 to have the entire system operating.

The original plan was for a 147 mile (235km) light rail transit, but examination of the finances indicated that potential revenue would not meet the cost of a 147 mile system by 2010. In 1986, the plan was revised to a 93-mile LRT system with about 7 miles (11km) aligned beneath the Central Expressway between Mockingbird Lane and downtown Dallas. Such a system was affordable but only with long-term debt comprising bonds or notes that mature in five years or more. To go into longterm debt, DART needed the approval of its member city voters.

In a second referendum in 1988, 58% of taxpayers who voted in the bond election opposed long-term debt to build a rail system and objected to any rise in the 1% sales tax.

DART went back to the drawing board to develop a new system plan that could be implemented using local funds on a pay-as-you-go basis using short-term borrowing and available State and Federal funds as well as the revenue already collected from the ongoing 1% sales tax levy.

After months of work and a series of public hearings, DART adopted a new 20 year plan in June 1989, almost one year after the failed bond election.

This total $4.1 billion (inflated dollars) plan is a much scaled down version of the original scheme and is based on 37 miles of HOVs with 67 miles (107km) of light rail transit and 18 miles of commuter rail. This included a plan to run the LRT in boxes either side of the depressed Expressway which has since been abandoned for the cheaper tunneled option which also can be completed earlier.

DART has bought more than 90% of the railroad right-of-ways or operating rights on existing rail lines required by the light rail and commuter rail systems.

The remainder of the property needed is either in utility or city-owned rightof-ways. A clause in DART’s approved plan makes provision for eventually relocating the system underground in the central business district when ridership reaches 8,000 riders/peak hour in each direction with train frequency of more than one every 2.5 min in each direction.

Total estimated cost of the current 20 mile (32km) LRT starter system with its 21 stations, including rolling stock, purchase of rights-of-way and a maintenance facility, is about $828.7 million. Construction and implementation of the system to meet the 1996 commissioning date is to be funded from DART’s three main sources of income - 73.5% from the 1% sales tax levy (which earns about $180-200 million/year and is split 50/50 between new capital projects and operating costs); 13.1% of Federal funding provided through the Urban

“As designed, the station structure, including the two 400ft long x 777ft2 (120m x 72 m2) station tunnels and 826ft2 (77m2) escalator tunnels, involves the excavation of about 45,000m3 of chalk,” said Gerhard Sauer, President of DSC. “Based on the Austrian code of rock classification, the initial support requirement is designed primarily to stabilize wide span openings and protect the exposed surfaces from weathering and raveling, rather than support various categories of rock quality.”

Initial support in the station comprises dowels or nontensioned rockbolts as required and a 2in (50mm) layer of steel fiber reinforced shotcrete. The finish is a 6-9in (150-230mm) thick unreinforced in-situ concrete lining.

There is no need for lattice girders and application of the steel fiber shotcrete need not be immediate. A thin

Mass Transportation Administration (now known as the Federal Transit Administration or FTA); and 9.4% from fares on the existing DART bus system.

Federal funds used to be allocated on a 90:10% local funding ratio for highway projects and a 70:30% ratio for transit system. Now the allocation is 80:20% Federal:local funding for both highways and transit projects. However, Federal resources for transportation projects have been scarce for some time and to give themselves a better chance of qualifying, each authority applying for funds provides an overmatch of local funds with the tables often almost reversed, with the authority providing 80% of local funding and applying for 20% from FTA. Of all DART’s capital expenditure to 2010, only about 30% is related to the LRT. About $10 million has been spent since 1989 on the initial design for the 20-mile starter system. The Engineer’s Estimate of $110 million for the civil construction of Cityplace station and its running tunnels stays within DART’s guarantee to the City of Dallas that turnout cost of this, the only underground section of the LRT, will not exceed $223 million.

“This is an important commitment,” said Jim Martin, Director of Construction Management for DART, “and we intend to do all we can to avoid cost overruns.” As recommended by the American Society of Civil Engineers, the bid documents will be placed in Escrow, a dispute review board of three independent experts, (one nominated by the client, one by the contractor and the other by those two themselves will be appointed), and both the client, the designer engineers and the contractor will participate in a partnering process.

Under a partnering process, introduced initially by the USA Corp of Engineers, managers of each organization attend seminars to improve co-operation between each and develop methods and skills of resolving problems amicably and swiftly on site.

skin of mortar slurry will seal exposed surfaces until the fibercrete is applied.

About 95% of the running tunnels will be finished with only a 2in (50mm) layer of steel fiber shotcrete. Cast concrete is specified for about 6,000ft (1,800m) of the total 30,000ft (9km) of twin running tunnels and there is provision for later addition of more in-situ concrete if necessary. A waterproofing system is specified in certain areas of the station and tunnels where water is anticipated but this amounts to only about 5% of the total excavation. “Under these circumstances, excavation can progress more rapidly than would be the case in poorer ground where more initial support is required.

The subsequent savings in time and material costs are significant,” said Sauer.

21

Fig 1. Cityplace Station will be excavated from the Austin Chalk geology using NATM

In order to confirm the Engineer’s Estimate, DART requested a review by a panel of experts who examined the preliminary plans, constructability, cost estimates and schedules of the proposal. This exercise predicted that the tunnels would be between $40 and $60 million cheaper than the boxes. Armed with such information, as well as the scheduling and cost comparison with the box option, the DART board accepted the tunnel plan for Cityplace in June 1991.

As one of the largest contracts on the starter system, it was imperative to have construction of Cityplace Station and its tunnels started in early 1992 to meet the starter system’s 1996 operation date. Huitt-Zollars with subconsultants Sverdrup Corporation, HOK Architects, Dr Sauer Corporation and HDR Engineering, moved into a fast track design phase in order to have bid documents released by mid- 1991. The bid documents were prepared for the entire 3.2 mile (5.5km) section including the 120ft (36m) deep station in 3.2 months.

Bid opening

At the public bid opening in December 1991, SA Healy emerged as the lowest of the eight competing bidders with a bid of $86.8 million. Obayashi Corporation of San Francisco was second at $87.73 million and the third was from the Gilbert/Shea JV of Omaha at $87.78 million. The highest bid at $115.6 million was submitted

by Ebasco Constructors. All bids were based on a phased construction concept which provided 100% design for civil, structural, and geotechnical elements and a 30% design for mechanical, electrical, and architectural finish components, included in the bid as allowance items. “While this is an unusual approach to government sector contracting procedures, it is commonly used very

TunnelTalk references •

Exploring critical elements for NATM success - June 1995

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Tunnel too rich for Dallas taxpayers - March 2009

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Bidding signals start of San Francisco subway - June 2011

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Central Subway bids open in San Francisco - April 2013

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NATM breakthrough on East Side Access - October 2012

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Metro stays underground at Dulles Airport - April 2011

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Constant face surveillance - November 2009

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Design-build experience in Puerto Rico - December 1999

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Celebrating 30 years of efficient design in USA - June 2017 22

successfully in the private sector,” said Martin. “I am sure our success will be followed closely by the industry.”

Exploded fallacies

Healy’s winning bid for both the underground station and the tunnels is within $1 million of its next two rivals and $35 million below DART’s $122.4 million budget for this portion of the line. These figures explode an oftenheld assumption that underground work is, by definition, the most expensive of all options. They also reflect a confidence the contractors have in the favorable tunneling conditions in Dallas. “Many of the bidding contractors, including the three lowest, have had recent tunneling experience in this type of ground,” explained Martin.

Gilbert has just finished the 22ft (6.7m) diameter North Central drainage tunnel in preparation for the Expressway upgrade, using a Robbins fullface TBM and installing no immediate support. After standing unsupported for many months, the tunnel is now being finished with a 1ft (300mm) thick unreinforced in-situ concrete lining.

In 1989, SA Healy completed the Govalle sewer tunnel network in Austin in similar chalk geology, using a Robbins hard rock TBM and two Lovat shields of between 8ft and 11ft diameter (2.5m and 3.3m respectively). The Robbins TBM drive was finished with an in-situ concrete lining while both Lovat drives were temporarily supported with ribs and lagging and finished with in-situ concrete.

“In Dallas we intend to use a reconditioned Robbins TBM for the tunnels and three, new roadheaders for the station excavation,” said Giorgio Petrangeli, President of SA Healy. Although not yet finalized, Healy plans to break out of the tunnels for concurrent excavation of the station.

At the south portal, two short NATM tunnels of about 120ft (36.5m) are expected to be excavated by roadheader to pass through the softer material and into the chalk.

The Robbins TBM is the machine SA Healy used in joint venture on the Rogers Pass railway project in Canada.

“Because the TBM worked in harder rock in Canada, it will be more powerful than strictly necessary in Dallas,” explained Volker Meldner, Vice President of SA Healy.

“Its cutterhead also needs to be reduced from the 22ft Rogers Pass diameter to the 20ft 6in (6.5m) diameter needed in Dallas.”

The refurbished TBM is expected to advance about 2,000ft (600m)/month or between 100-150ft (30-45m)/ day working three shifts/day, five days/week. Both tunnel

drives are expected to be excavated in about seven or eight months each, with the station excavation taking about nine months. Concreting of the running tunnels

is expected to take four months with final lining in the station taking some four months. Healy expected to hand over the completed job in September 1995.

Cityplace NATM and TBM excavations SITE VISIT REPORT: MAY 1994

A

t a second visit to the project in 1994, it was evident that excavation on the Cityplace contract in Dallas was far from routine for SA Healy of McCook, Illinois, now a wholly owned subsidiary of Impregilo SpA of Italy.

Record TBM rates, continuous conveyor mucking, as well as contaminated ground delays, polyfiber shotcrete and NATM station design all set the Cityplace contract apart from the usual.

As the only mined underground section on the 20 mile starter network, the contract comprised twin 16,760ft (5km) x 6.5m diameter running tunnels and excavation of two large underground metro stations the most complex of which is Cityplace.

Much of the heightened involvement arises from the fact that, due to DART’s complicated pre-bid history, only 30% of final design was complete when bids were called in early 1992. “For this reason, the contract is working more like a design-build job,” said David Rogstad, Project Manager for SA Healy. “With final design progressing with construction, we are contributing a great deal to final design discussions. There have been a tremendous number of changes and contract additions which have taken our original bid price of $70 million to about $91 million in March 1994.”

Through partnering, decisions have been made in a matter of days and potential problems have been avoided.

Partnering was adopted from the start of the project and has opened clear lines of communication between Stone & Webster Engineering Corp., DART’s construction manager, and the large design group which includes Huitt-Zollars of Dallas, Sverdrop Corp of Boston, HDR of Dallas, Lachel and Associates of Golden, Colorado, and DSC, the Dr Sauer Corp of Herndon, Virginia.

Contamination

Like its six competitors, SA Healy chose to excavate the running tunnels through the good quality Austin Chalk using a full face TBM. After contract award in February 1992, a refurbished Robbins machine was launched from the open cut portal ramp at the north end of the contract in November 1992.

the TBM and progressed through the faulted zone. This revealed a series of three open faults of up to 18in high and 6in wide over about 50ft (15m) of tunnel. After exposure, the joints were mined out and plugged with lean concrete to about 10ft (3m) from the tunnel wall on both sides. The same was repeated in the north bound tunnel before TBM tunneling resumed in January 1993.

Healy’s tunneling crews also had to be trained to work in hazardous ground conditions which included wearing protective clothing and complying with other regulations from OSHA, the USA occupational health and safety authority.

Then 10,000ft (300m) later, an unexpected reading of methane caused the second major shutdown. OSHA regulations require that all underground work sites monitor for methane and other hazardous gases, but methane was not expected in Dallas. A 2.5 month shut down was needed to fit explosion proof and automatic shut off facilities to the TBM’s electrical system and to upgrade the heading ventilation system substantially. As it happened, methane readings were low and caused only few short stops. Studies indicate that the methane is migrating slowly from a deep source of up to 2,500ft (750m) beneath the surface.

Through both of these situations, Healy’s cash flow was protected by the client’s agreement to pay for work as it progressed. Partnering avoided potential contractual impasse or later resolution of difficult outstanding claims arising from the problems.

Station excavation

Contrary to original design assumptions, Healy chose to excavate the TBM tunnels through the Cityplace Station before starting cavern excavation. At the same time, in August 1993, station construction started with top down excavation of the ventilation shafts, the main passenger access and emergency evacuation accesses (Fig 1).

Secant piled walls in the shafts and slurry diaphragm walls in the large box openings preceded topdown excavation through the 20ft (6m) of waterbearing topsoil sands and gravels. Then, as the AH Beck system of blind hole

Just 400ft (120m) into the first drive, the Refurbished Robbins TBM ready for its adventurous and record-breaking drive TBM ran into a system of open joints which run across the alignment and had become filled with gasoline fuel and toxic cleaning solvents introduced either from a leaking underground fuel storage tank or from a maintenance workshop business above which has long since closed and been demolished. It took 2.5 months to deal with the situation.

Using a small roadheader, a heading was advanced down the alignment of the parallel north bound tunnel. On nearing the fault zone it cut across in front of 23

as well as increase them in reaction to more difficult conditions.”

Tight control of station and tunnel excavation in Dallas however is vital. The station and tunnels run directly beneath the reconstruction of the I-17 highway which is being enlarged to eight lanes and depressed into a deep open cut. The station invert lies about 100ft (30m) below the bottom of the new highway and very close to the foundations of the multi-story Cityplace office building, which is connected directly to the station through the basement.

Continuous conveyors contributed to record advance rates

shaft drilling was working on the four 20ft (6m) diameter x about 130ft (40m) deep ventilation shafts, the first of five roadheaders to be used for station excavation was advancing the 1:1.7 or 30° decline to the 90ft (27m) deep mezzanine chamber and on down the escalator and stairway decline to the station platform caverns.

From a break out chamber at the bottom of each shaft, a small Webster roadheader from the UK was lowered down the shafts to continue excavation, hauling muck through the shafts. “We saved about three months by excavating the ventilation tunnels from the surface,” said Rogstad.

Having gained access to platform level, the large Eickhoff roadheader boom fitted on a tracked Koehring backhoe chassis was put to work enlarging the 21ft 6in (6.5m) diameter running tunnels to the 27ft high x 32ft wide (8m x 9.7m) platform caverns. After completing the second TBM drive, the continuous conveyor was left in place to transport station muck to the same surface stockpile.

Glass fiber rockbolts were installed in the 480ft (146m) long platform cavern area during running tunnel excavation.

The Koehring/Eickhoff roadheader has the reach to enlarge the platform caverns to their full 775ft2 (72m2) cross section in one pass, but the NATM design requires a top heading and bench sequence. This is satisfied with a large 20ft (6m) deep (370 ft2 (34m2)) top heading leaving the lower part to be benched to track level.

Healy is not a new-comer to NATM. It brings valuable experience to the Cityplace contract from its Cumberland Gap twin tube road tunnel contract in Kentucky where it used steel fiber reinforced shotcrete, monitored geomechanical instrumentation and installed a plastic membrane waterproofing system, all according to specifications prepared by DSC as specialist NATM designer (see page 30). For Cityplace, Terra-Mar was subcontracted to purchase and install the instruments.

Terra-Mar is also quality control checker of shotcrete test samples and other construction products.

In the good quality chalk in Dallas, the instrumentation is being used principally to verify design assumptions rather than driving cost effective design changes. As Rogstad explained: “The construction industry in the USA is driven primarily by liability which leads to a more conservative approach than perhaps in Europe. For this reason it is difficult to apply the NATM concept to reduce support elements in better-than-expected conditions 24

Geotechnical readings are passed from Healy to construction manager Stone & Webster which instructs the contractor after interpretation by DSC and Lachel, the two specialist tunnel support and lining designers with full time design representatives on site.

Although relatively dry, the porous Austin Chalk is susceptible to increased water content after heavy rainfall. To avoid potential water seepage and future maintenance problems, the plastic membrane waterproofing and drainage system is being installed by specialist subcontractor Wisko. This will be covered with the nominal 1ft (300mm) thick in-situ concrete lining which is reinforced with a single mat of rebar.

TBM record rates

Outside the two geological interruptions, Healy’s TBM excavation operation hit record levels. The first tunnel (started on 1 November 1992) holed through at the south portal cut-and-cover ramp on 17 August 1993 including more than 5.5 months delay. The second tunnel started back at the north portal on 27 September 1993 and broke through just more than four months later on 3 January 1994. On the way the TBM clocked a daily best of 114.6m (376ft) in three 8h shifts/day, a best week of 500m (1641ft) and a best month of 1,832m (6,012ft). A best 8hr shift of 45.1m (148ft) completes a record breaking set of performance rates acknowledged by Robbins which built the machine for Healy in the late 1970s for a Chicago TARP contract and working on the Rogers Pass railway tunnel in Canada before coming to Dallas.

These remarkable rates were made possible, according to Rogstad, by the competent, weak to medium strength Austin Chalk limestone, outstanding supervision, and a continuous conveyor muck haulage system. “Our average of 248ft/day in the second tunnel would have been impossible with rail bound muck haulage,” said Rogstad.

“Recent continuous conveyor operations indicate that rates of +200ft/day are possible with belts, where 100ft/ day is the average to be expected with muck trains. The 4% tunnel gradients would also have created difficult uphill hauls for full muck trains. Logistics here were ideal for a continuous conveyor.”

The 30in (750mm) wide belt from Continental of Winfield, Alabama, travelled at a speed of 800ft (240m)/min providing a haulage capacity of 750tonne/hr. A new extension of 1,500ft (450m) had to be spliced in every third day or so. To control dust problems, the TBM has two dust scrubbers and a fabric screen was required to reduce wind blown dust off the surface muck pile before being transported to the final disposal site. A foam product added to the muck on the conveyor system was said to be an excellent dust controller.

In addition to high capacity muck haulage, the conveyor frees up the rail track to keep up with tunnel supplies. In the competent limestone, support is principally with rock dowels and reinforced wet mix shotcrete. In the running tunnels, 10ft (3m) long No 8 Dywidag rebar bolts are installed on a systematic pattern of four bolts/5ft (1.5m) and are fully bonded with Celltite epoxy resin.

Polyfiber shotcrete

Instead of wire mesh or steel fiber reinforced shotcrete, Healy is using cofibrillated polyfiber supplied by Fibermesh of Chattanooga, Tennessee. “The polyfiber is slightly more cost effective than steel and it eliminates corrosion concerns,” explained Rogstad. But perhaps most significantly, it eliminates the need for a topcoat of plain shotcrete to protect the plastic waterproofing membrane installed in sections of the running tunnels and most of the station excavations. Polyfiber is much less abrasive also on the mixing and shotcreting equipment.

To meet the ASTM C1018 flexural strength and toughness test for fiber reinforced shotcrete, Healy is using 10lb of polyfiber/yd3 of wet mix shotcrete. The maximum water/ cement ratio is 5.18 gal/sack of cementitious material or 0.43lb/lb to give a water content of 28 gallons/yd3 and a maximum placement slump of 5in (125mm). Six to 10oz/cwt of a water reducing admixture is included together with an aluminate-based accelerator in the quantity of 5% by weight of cement. The minimum cementitious content/yd3 is 644lb or 6.85 sacks of Type II cement and 147lb or 1.96 sacks of fly ash. The aggregate per cubic yard is 793lb of maximum #8 pea gravel and 1990lb of concrete sand.

Paradoxically, the flexural strength and toughness of the shotcrete is said to not increase with higher compressive strength. A perfect concrete mix with an even distribution of fiber is needed for optimum tensile strength. More fiber is needed to increase tensile strength but at 10lb/yd3 Healy is near the upper limit of polyfiber without causing balling problems. The design specification requires a compressive strength of 5,000 psi after 28 days.

Healy’s on site batching plant is producing about 200yd3 of wet mix shotcrete/day. This is transported into the tunnel by 12yd3 Moran cars and transferred into one of two Maxcrete surge and remixer hoppers. These feed shotcrete units which comprise a Schwing 750 pump each, with a home-made robotic arm with a reach of 30ft (9m). The Schwing pumps provide a pumping distance of about 500ft (150m) from pump to nozzle and a maximum placing capacity of about 25yd3/hr (20m3/hr). Of this, Healy is using a capacity of about 10yd3/hr.

In the running tunnels, the design required that the ground be sealed within 24hr of being exposed. The Austin Chalk, although competent and with a very low permeability, has a 12% moisture content. On exposure, the moisture dries rapidly causing large shrinkage cracks which significantly reduces the limestone’s natural integrity.

To avoid the mess and logistics of shotcreting off the TBM’s backup, Healy chose to apply the minimum 2in (50mm) of shotcrete as a second pass, using a sodium silica product

to meet the sealing specification. The tunnel walls are washed down with high pressure water before the clear, hard sodium silica or water glass is painted on. The sealer was said to have applied well to the exposed limestone and there have been no reported bonding problems between the sealer and the shotcrete.

Progress

During the site visit in early March 1994, excavation of Cityplace Station was 60% complete and was on track for the revised contract completion date of 1 January 1996. In the meantime, 30 cross passages need to be cut and work progresses with shotcrete final lining in the running tunnels and construction of steel and wooden formwork ready for in-situ concrete casting. Custom built steel forms supplied by CIFA of Italy and Symons of Des Plaines, Illinois, will be used for longer lengths of uniform section excavations but special one-off wooden forms are required for the complex geometrical shapes introduced by the flexible NATM design.

Some 2,000ft (600m) of the running tunnels is also finished with in-situ concrete. This includes the zones adjacent to cross passage openings and where the tunnels pass close to existing underground services. It also includes the portal areas and particularly the south portal where mixed face conditions presented the most difficult tunneling on the project. Over the last 250ft (76m), the running tunnels rise into a mixed face of limestone in the bottom and wet sands and topsoils above. A section of cut-and-cover work provides access to the bored tunnel portals, the crowns of which lie about 40ft (12m) beneath the depressed highway deck.

A design for pre-support using grouted spiling was made available by DSC for this section but Healy chose a more traditional method using steel channels over rolled ribs.

Healy felt that grouted spiling using cement grout would be very difficult in sands where more than 40% pass the #200 sieve. Chemical grouts which could have been effective were prohibitively expensive. Conventional excavation was said to progress relatively well overall with only one instance of minor ground loss (5-7yd3) occurring near the portal of the first tunnel. The sands were excavated by hand and the chalk bench taken out with a roadheader. The south portal section of cut-andcover junctions with an adjacent cut-and-cover contract which brings the DART alignment to the surface for at grade passage through the downtown area.

The Cityplace contract has always been on the critical path of DART’s $844 million starter system to meet the projected commissioning date of Waterproofing as part of the NATM design Fall 1996. Some of the time lost has been made up and partnering greatly limited the time that could have been lost. To help keep the project on schedule, Healy has been awarded construction of Mockingbird Station at the north end of its core contract as a negotiated addition. This will save significant time over leaving its construction in the adjacent contract, which is a large contract in itself, and will include SA Healy when it is bid in April 1994. Meanwhile crews continue to complete the Cityplace Station and tunnels, described as the jewel in DART’s starter system. n 25

Combined road and rail access CASE STUDY: There are few examples of dual-purpose shared underground space infrastructure. There is the famous SMART stormwater and road tunnel in Kuala Lumpur, Malaysia, built primarily to protect the city from devastating flash floods and doubling when not required for water flow as a four-lane, double-deck cars-only toll road. In Alaska, the Whittier road and railway share underground space as an alternating one-lane toll road and accommodating trains on their schedule. Sharing underground space seems a logical, mutually beneficial, cost sharing option if service owners, insurers and designers would consider the possibilities, cooperate and expand their field of vision. The Whittier road-rail project in Alaska in the late 1990s illustrates how all three parties came to agree its dual purpose solution that continues to serve today.

SITE VISIT REPORT: FEBRUARY 1994

L

ocated at the edge of Alaska’s famous Prince William Sound, about 76km southeast of Anchorage, Whittier is among the most northern ice-free deep-water ports in the USA. The single-track railway, built for strategic purposes by the USA Army in 1943, passes through the surrounding mountains in two tunnels of 4km and 1.5km long. From the marshalling depot near Portage, the 20km one-way shuttle journey takes about 30min with a much reduced service operating in winter.

With financial support from the USA Federal Highway Administration (FHWA), the Alaska Department

of Transportation and Public Facilities (ADOT&PF) implemented the Improved Whittier Access Project in March 1993 when it engaged the Anchorage office of HDR Engineering to evaluate the feasibility of several improvement schemes studied over the years. Under the 20-month, $1.5 million contract, HDR completed a Location Study Report (LSR) and a federally-required Environmental Impact Statement (EIS) before the project moves into detailed design (Phase 2) and construction of the chosen scheme (Phase 3), if a build alternative is selected.

Options

Improvement options start at about $28 million to improve the existing rail shuttle service, through to more elaborate schemes involving new purpose-built tunnels for a dedicated Fig 1. Combined road and rail use of the existing 4km long railway tunnel is the most viable option

Table 1. Ten options for improving access to Whittier. The first six are considered most viable with others impractical on cost 1

An improved shuttle service

2

Joint car and train used of both existing tunnels with staging near Williawaw Campground and West Camp in Whittier

3

Joint car and train use of the 4km long Whittier tunnel from Bear Valley to West Camp without widening the tunnel

4

Joint car and train use of the Whittier tunnel with widening to allow one lane and a hard shoulder

5

New two-lane car tunnel parallel with existing Whittier tunnel with Bear Valley access to tunnel along Portage Lake

6

A new overland road via Portage Pass with Rear Valley access along Portage Lake

7

A new one-lane car tunnel parallel with the existing Whittier tunnel with Bear Valley access along Portage Lake

8

Widening of the existing Whittier tunnel to allow for two lanes of roadway and adjacent to the railway tracks

9

Widening of both existing tunnels for two-way car traffic and discontinue the train shuttle service

10 Joint car and train use of Whittier tunnel with widening for two lanes, one shared with the rail tracks 26

for Whittier, Alaska road link costing an estimated $200 million. In between there are several options which propose sharing the existing 4km long railway tunnel. While there are many level crossings in the world, this would be one of few instances where cars and trains share the same tunnel facility.

The most expensive shared proposal is to enlarge the tunnel to accommodate a two-lane highway adjacent to a railway compartment. Under the least expensive option, the one-lane existing tunnel would carry east and west bound road and rail traffic alternately, with manned control stations at both portals coordinating the schedules.

As specialist sub-consultants to HDR, Lachel & Associates of Golden, Colorado, is engaged for geotechnical and tunnel design expertise. Mott MacDonald of the UK is studying tunnel ventilation and HDR is covering road building requirements.

State approval of the project, together with federal funds available through the FHWA Intermodal Surface Transportation Enhancement Act of 1991, secures a possible funding allocation of some $78 million. Of this, ADOT&PF has set a preliminary project budget of $50 million which readily eliminated the most expensive options, leaving six of the ten original alternatives recommended for further study (Table 1).

Although a vital lifeline to Whittier, the shuttle train service runs at a loss, with ARC subsidizing it from its own revenues. Without outside subsidy, it is not economical for ARC to increase the service, and the cost of improving present travel times would have to be passed on by way of higher ticket prices.

Options for new roads are likely to be rejected as too expensive to build and maintain. Several bridges and other special structures such as snow sheds and possibly tunnels would be required. Avalanches would be a major concern in winter and snow drifts of up to 20ft (6m) would need to be cleared to keep the road open. Sharing the existing underground space appears the most viable proposal at present.

Joint use

“As owners of the rail tunnels, we are not that enthusiastic about sharing our facility,” said Tom Brooks, Chief Engineer for ARC, “but ARC agrees that improved access to Whittier is desirable and, since we cannot provide that ourselves without subsidy, we are cooperating with the current ADOT&PF investigations.”

Among its provisos for joint use, ARC insists that even if its passenger shuttle service is superseded by current plans, it must retain adequate use of the tunnel for its profit-making freight operations.

Whittier is the only connection between the State railway system of Alaska and that of Canada and the lower 48 States of the USA. The regular rail barge schedule which provides the link is one of the last rail-barge services in the world and earns ARC some $6-8 million in freight revenue per year, as compared to the $2 million earned by the shuttle service.

In addition, ARC will not contribute to the cost of construction and work must be completed within specified windows without seriously disrupting train schedules. In the completed scheme, rail would likely have priority over road traffic during non-peak times.

According to Dennis Lachel, President of Lachel & Associates, the single track tunnel is in relatively good condition. “It was excavated in the early 1940s by drill+blast mainly through Graywacke which, although heavily jointed, is stable. There is minor instability in the side walls and in-situ stresses keep the arch intact. There is very little support installed either initially or subsequently, and while there is evidence of rockfalls over the years, this is not excessive. Even after the devastating earthquake of 1964, only three cars of debris were removed from the unlined tunnel.”

For combined-use proposals, the minimum structural modification in the tunnel would be excavation by drill+blast of a series of pull outs along its 4km length (Fig 2). “Structural work would start with a thorough

From left: Fig 2. Combined use of the existing railway tunnel would require re-excavation to provide either regular turn outs or a single lane plus full length hard shoulder; Fig 3. Option 8 proposed two vehicle lanes with a single-track railway alongside

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scaling programme,” said Lachel, “followed by installation of extra support where necessary, using rockbolts, shotcrete and wire mesh.” A more detailed survey of the tunnel will determine the remedial work required and allow calculation of more accurate cost estimates for the various combined-use proposals.

“Dealing with ground water ingress could be the single most expensive and difficult task,” said Lachel. A plastic membrane waterproofing system may be required and the installed drainage system would have to resist freezing in the winter. Although temperatures fall to below -20°F in winter, the site is not subject to permafrost. Major construction work would be programmed in the low-traffic winter months with the working environment maintained at reasonable temperatures by closing doors which exist at each portal to prevent snow drifts and freezing conditions on current tunnel operations.

Ventilation

Ventilation and emergency evacuation are major elements of the engineering study. “The project design year is 2015 when average daily traffic is projected at 4,500 vehicles/day,” said Alan West, Ventilation Engineer from Mott MacDonald. “This is not high but the ventilation system must also purge diesel fumes created by the trains. A longitudinal ventilation system with jet fans at regular intervals or at the portals would be the least expensive option, but many factors must be investigated. These include the high wind velocities over Portage Pass caused by the many glaciers in the vicinity, as well as the prevailing barometric pressures and seasonal variations in wind speeds. There is also

the possibility of using the adjacent petroleum-oillubrication (POL) tunnel to assist ventilation and provide for emergency escape.”

The POL tunnel was excavated by drill+blast in the 1960s by the USA Army to carry an 8in diameter fuel line from its tank farm west of Whittier port to depots in Anchorage. The 2.5m x 2.5m unlined tunnel runs parallel with the existing rail tunnel at about crown level and is between 40-80m center to center. Maintaining the integrity of the POL tunnel is a major concern for rail tunnel modification plans, as is security of the 12kV power cable and the fiber optic telephone cable which pass through the tunnel to supply all power to Whittier and link it with the outside world.

Implementation

Whichever alternative is chosen, there are several ideas for its implementation. These range from a conventional construction contract to more non-traditional design-buildoperate schemes. “A design-build-operate concession of about 20 years is favored because it will encourage competition among the most creative minds in the field,” said Jerome George, Chief of the Consultant Contract Management Department of the ADOT&PF and leading proponent of the project. “What the final scheme looks like, and how the concessionaire runs it, is their concern as long as our detailed designs and operating criteria are met.”

With State and Federal funding for the scheme already in place, many of the risks otherwise faced by a potential private developer are removed. “We have looked at private enterprise schemes in the past,” said George, “but these have failed largely because developers included a high contingency element to cover potential risk. Under the current proposal, the private developer will construct the selected alternative and operate the toll scheme on behalf of the State. There is no need to borrow money, and any shortfall in toll revenue to cover operating and maintenance costs will be underwritten by the State. In addition, all necessary permits and approvals for the scheme will be secured by the State ahead of construction. The concession selection criteria will depend on the efficiency of the traffic handling and toll gathering systems.”

Feasibility of a toll concession appears assured. Whittier, on Prince William Sound and close to Anchorage, is a popular tourist destination. Tourism is the third most important industry in Alaska next to oil and fishing. In addition to greater access for tourism and recreational activities, the project would allow faster response to medical and ecological emergencies such as the infamous Exxon Valdez oil spill in Prince William Sound. It would also improve Whittier’s fishing industry by allowing fresh catches to be taken more rapidly to Anchorage for export by air freight and would prevent boat owners risking their lives to get back in time to catch the last shuttle train out.

Any scheme to improve access to Whittier will have to evaluate the impact on the pristine environment of Portage Lake and its glacier, Alaska’s most famous tourist attraction

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However, as Eric Keen, Project Manager for HDR explained, there is much to be done before the EIS of the preferred scheme is concluded in December 1994 and invitations to tender for the Phase 2 detailed design contract are advertised in early 1995. “There are many environmental issues still to be examined, particularly those relating to increased human activity in Whittier, on Prince William Sound and in the Whittier area. These will have a major impact on the local community as well as on State-wide organizations.”

From left: Dual road-rail facility; Jet fans provide for longitudinal ventilation; Portal structures protect against avalanches

Concerns include: • Increased demands on Whittier’s public facilities such as sewerage, waste management, water and power supply, parking and accommodation facilities, as well as the police, fire bridge, search and rescue operations and communication needs; • Changes to Whittier’s quality of life, the impact on property values and the growth of new businesses and residential zones; • The impact of Whittier’s development on other centers of tourism, fishing and commerce in Alaska; and • The allocation of State and Federal funds to other regions, given the large investment proposed for such a small permanent community in Whittier.

In addition, there are many outstanding engineering concerns such as: • How are pedestrians and bicyclists to pass through a combined use tunnel?

• How will a combined tunnel operate?

• Where and how is traffic to be marshalled between train runs?

• Where can tunnel muck be disposed of? and so on.

To ensure that all points of concern are addressed, the ADOT&PF has adopted the partnering concept among all companies involved. HDR is also managing a comprehensive public involvement program, conducting scoping meetings and workshops with various special interest groups, and coordinating communications between government agencies and the general public.

It has also produced an informative documentary video on the project. While environmental and engineering concerns continue to be addressed, those interested in competing for Phases 2 and 3 are advised to be ready with imaginative proposals for when invitations to bid for this unusual transportation project are called.

Construction phase

Four years later, in June 1998, Kiewit Construction was awarded the construction project. The $57.3 million design-build contract converted the existing 13,100ft (4km) long single-track railway tunnel into a dual use road and rail facility. With funding provided 80% by the USA Federal Government transportation authority (FTA) and 20% by matched State funding, Hatch Mott MacDonald provided engineering services to the design-build contract including ventilation; emergency egress and life safety systems; tunnel lighting; sophisticated electronic control systems for the dual purpose transportation facility; ground support; water/icing control; the road/rail tunnel

invert design; and the tunnel portal structures. Design also included the civil works needed to increase the dimensions of the tunnel to accommodate double-deck railroad cars and construction of eight emergency turnout niches. The upgraded tunnel is supported with rockbolts, wire mesh, and shotcrete. Although temperatures fall to -20°C in winter, the tunnel site is not subject to permafrost and the installed drainage system will have to resist freezing in winter.

Work on the tunnel started in September 1998 and construction progressed over a schedule of possession windows of four to six days designed to sustain a full rail service during the contract period. Tunnel outages were scheduled during the 1998/99 winter months when much of the enlargement excavation was undertaken and when a new precast road deck with embedded rail tracks was installed.

Each 125ft (38m) long emergency turnout leads to a fireproof structure which can accommodate 55 people.

Each refuge has a dedicated water supply and special ventilation system.

When opened to traffic in June 2000, the tunnel began its operation as an alternating one-lane toll road facility during daytime hours and accommodated eight train services per day on the single track embedded in the precast concrete single lane road and rail invert.

For Kiewit, Mike Colpack was Project Manager and Ken Stollenmaier was Tunnel Superintendent. Frank Frandina was Project Design Manager for Hatch Mott MacDonald and Chris Tattersall the Quality Control Manager. When opened and as part of its contract, Kiewit operated the facility and provided maintenance for the following two years before ownership was transferred to the Alaska Department of Transport and Public Facilities.

Credit where much is due

In recognition of the achievements, the project received several prestigious engineering awards. These are a tribute to the overall efforts of the Alaska Department of Transportation and Public Facilities in promoting and progressing the project and to the project’s consultants and contractors for bringing it to reality. n

TunnelTalk references •

In search of resilient cities - December 2011

•

Legacy of underground infrastructure - December 2021 29

CASE STUDY: Steel fiber shotcrete as a substitute for wire mesh, extremely variable geology and the concept of partnering identified the twin-tube Cumberland Gap road tunnel in the early 1990s as a benchmark project in the development of NATM and its growing acceptance in North America.

Cumberland Gap

advances NATM in the USA

SITE VISIT REPORT: JUNE 1992

T

he need for a road tunnel through the Cumberland Mountain in the Tri-State region of the Appalachian Mountains between Kentucky, Tennessee and Virginia has been recognised since the mid-1950s. In the early 1990s, some 18,000 vehicles/day used the existing two-lane road as a major route through the mountains (Fig 1) but single-lane traffic on the steep winding mountain pass becomes congested in summer when tourists visit this historic national park, and in winter when snow and ice is hazardous.

The new 4,600ft-long twin-tube tunnel will cut only 1 mile off the existing 4 mile journey over the mountain but it will eliminate one of the worst bottlenecks and accident black spots on the US highway system. Once the new route is open, the existing road will be decommissioned and the National Park will be restored to its historic wilderness.

Extremely variable geology was always expected to present the greatest challenge to the proposed twintube highway tunnel. The sedimentary sandstone of the formation is blocky and fractured, with interspersed coal and shale deposits, while extensive cave systems occur in the limestone, which is more competent but highly porous.

Construction started in 1985 with a 10ft x 10ft length pilot tunnel along the southbound tube. This was designed by the client with assistance from Golder Associates of Atlanta and was completed in December 1987 for a total cost of about $3 million.

From the geotechnical information supplied by the pilot tunnel and other site investigation reports, principal project consultant Parsons Brinckerhoff Quade & Douglas (PBQ&D) prepared a cost estimate for a NATM-type design with a longitudinal ventilation system. However, before awarding the main excavation contract, the client investigated ways to reduce the original cost estimate.

It commissioned a value engineering proposal managed

by A Benesch of Chicago which in turn engaged a review board comprising representatives of six major civil engineering firms in the USA. One review member was from the Dr Sauer Corporation (DSC now Dr Sauer & Partners) of Herndon, Virginia, as a specialist tunnel subconsultant. “The value engineering exercise presented two principal modifications which reduced the original estimate substantially,” said Otto Mayr, Project Manager at Cumberland Gap for the FHWA. Both recommendations: • use of lighter lattice girders for a more modern NATM excavation and support approach; and • confirmation of the safe applicability of longitudinal ventilation, eliminating the need for a false ceiling in the finished tunnel had the immediate effect of reducing the excavated crosssection. At the time, longitudinal jet fan ventilation had been accepted by the Pennsylvania Turnpike Commission for the second tube of its 1,200m-long two-lane Lehigh highway tunnel near Allentown. Longitudinal ventilation at Cumberland Gap saved about $20 million over a semitransverse system.

Reduction of the excavated cross-section left the pilot tunnel in the crown of the original cross-section higher than is now necessary. As a result, the cross section of the southbound tube was increased to incorporate the pilot at its higher elevation. The full cross-section of the southbound tube is 1,206ft2 while that of the northbound is 1,030ft2 (Fig 1).

The NATM concept brought with it several other advantages, such as more economic use of time, labour and materials as well as providing for installation of an efficient waterproofing system, a major concern in this geology and climate.

The revised design was accepted, and DSC was retained as a sub-consultant to principal construction engineer, Vaughn & Melton, to supervise the construction phase.

With 18 associated contracts, including demolition of the

Left: Previously excavated pilot tunnel in the top heading of the southbound tube Right: Fig 1. Twin-tube four-lane NATM highway link runs across the border between Kentucky and Tennessee

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existing road, the full project was valued at $250 million.

Of this the completed tunnel represents about 40%.

The main tunnel contract was awarded in January 1991 to the SA Healy/Lodigiani JV as the lowest of seven bids at $52 million and set against the Engineer’s Estimate of $69 million. The closest rivals to the winning bid for the twin-tube bored tunnel with a 500ft of cut-and-cover on the Kentucky side were the Dillingham/Obayashi JV at $55 million and the Grassetto/Incisa JV at $58 million.

The highest bid was $74 million.

Above: Fig 2. Cave systems identified by the pilot tunnel which were backfilled before excavation of the full tunnel Below: Caves in the limestone are large and extensive

From information made available from the pilot tunnel, the geology along the main tunnel alignment was divided into four support categories. In addition, and in accordance with the earlier PBQ&D design, the face was divided into six headings with the central crown heading being removed first and followed at various distances by the two crown shoulders, the central bench and finally the two bench shoulders (Fig 1).

For SA Healy, this is its first major NATM project. ILF of the US, engaged as specialist adviser, has provided an experienced NATM engineer to work on site. Healy has since been awarded the Cityplace NATM underground station contract for the Dallas Metro and is likely to retain ILF. DSC is also involved in the design of the Cityplace underground works (see page 19).

When SA Healy and its 25% JV partner Lodigiani won the contract, it proposed and had accepted two major changes to the envisaged method statement. First it proposed reducing the number of excavation headings from six to four: top heading, central bench and two bench shoulders blasted together. “We believed that the ground would be competent enough to allow excavation of a full 730ft2 top heading followed by removal of a full 300ft2 bench,” said Volker Meldner, Vice President for SA Healy. “In fact, the ground would in some cases support a single full face excavation cycle,” he added, “but on this occasion we are staying with the top heading and bench programme throughout.”

Second, the JV was permitted to take care of two identified series of caves from within the pilot tunnel rather than coping with them as the main tunnel advanced. Without knowing the full extent of the caves, Healy built bulkheads some 15ft outside the full tunnel profiles and backfilled the empty space. This was a major undertaking in itself and called for the pumping of more than 1,500yd3 of lean concrete as well as installation of an effective drainage system through the concrete plug to avoid build up of ground water pressure (Fig 2). When the main tunnel advances, Healy believes it will progress more safely through the backfilled caverns and voids with the risk of others being exposed as excavation advances.

“The top heading is about 40% complete,” said Jim Lewis, Project Manager for the contracting JV, “and thankfully

we haven’t run into any further caves so far.” A 20ft-Iong probe was maintained in the pilot tunnel and one of 25ft is being advanced in the main tunnel drives in areas where caves are anticipated.

It is important to maintain the existing groundwater regime through the caves since, for environmental reasons, groundwater cannot be deliberately channelled from one watershed to another, and the owners want to avoid handling vast volumes of natural groundwater in the drainage system. The natural ground water content is substantial and as much as 10,000 gal/min of water flows from the pilot tunnel after heavy rain. The associated plastic membrane waterproofing system of the revised design represents about $2 million or 4% of the awarded $52 million civil tunnel construction contract.

In addition, the FHWA, on recommendations from PBQ&D and Golder Associates, introduced a significant change to common European NATM practice. “Instead of using welded wire mesh for shotcrete reinforcement, we specified the use of fiber reinforcement to meet a given performance specification,” explained Bob Leary, Geotechnical Engineer for the project since 1984 and temporarily acting as Construction Engineer for the client. To comply with this specification, the contractor has elected to use 90lb/ yd3 of 1.5in-long steel fiber as shotcrete reinforcement. It could equally have chosen to use plastic fiber or different configurations and weight ratios of steel fiber.

“Although marginally more expensive at about $100/yd3 for unreinforced shotcrete and about $160/yd3 for steel fiber shotcrete, excluding accelerator, fiber reinforced shotcrete is much easier to handle than welded wire 31

Left: Fig 3. Steel fiber shotcrete withstands initial cracking and retains greater residual load-bearing capacity; Right: Shotcreting the tunnel portal with the Putzmeister TSA 12/4

mesh,” said Leary. “It eliminates one labourer and the time consuming process of fixing wire mesh from the working cycle, reduces rebound, avoids shadows behind the wire mesh, and places steel where it is needed most to increase the flexural strength of the shotcrete. However, it is more aggressive on shotcrete hoses and equipment and a layer of unreinforced shotcrete will be required over areas of steel fiber shotcrete to avoid damaging the plastic waterproofing membrane,” he added. “But these drawbacks are minor when compared with the advantages.”

While steel fiber reinforcement in shotcrete is used almost as a matter of course in Norway and other Scandinavian countries. In the USA, it was introduced in the tunneling industry only recently. Therefore, the FHWA has included a comprehensive testing programme for the steel fiber shotcrete at Cumberland Gap. Following a competitive bid procedure, the $600,000 contract was awarded by the SA Healy/Lodigiani JV to Bhate Engineering Corporation (BEC) of Birmingham, Alabama.

Shotcrete for Cumberland Gap is being bought ready mixed from a local supplier which has mobilised an independent concrete batching plant on the strength of the project. Steel fiber is bought by Healy/Lodigiani from Bekaert and is delivered to the batching plant.

Accelerator is added at the nozzle. Being delivered to site as a wet ready mix, the shotcrete must be applied within two hours. It is delivered mainly in 8yd3 concrete trucks with loads of 6 yd3 or 4 yd3 loads also possible.

On site, there are five BEC employees who monitor shotcrete quality both at the batching plant and in the tunnel. For every 50yd3 of shotcrete supplied, a 30in x 30in x 8in thick test panel is produced which is then cut into three 4in x 4in x 14in beams and subjected to various laboratory tests. Core samples of shotcrete are also taken at regular intervals from the tunnel walls for compressive strength tests.

“The objective is to ensure that the shotcrete performs to the necessary specifications as well as gather valuable reference data for future applications of steel fiber shotcrete in highway tunnels,” said Leary. “We in the Federal Lands Programme of the FHWA undertake implementation efforts to try out new techniques and promote the most successful. While there is already a great deal of information available from other countries about the technical properties of steel fiber shotcrete, it is the implementation under actual project applications which we need to monitor.” The contractor is directly involved in the monitoring process since the unit price 32

for shotcrete is paid according to its quality on a sliding scale of acceptance.

Beam testing of the fiber reinforced shotcrete is based on the standard C-1018 American Society for Testing and Materials (ASTM) test. This test specifies particular deflections related to the deflection at first crack, where load carrying capacity must be maintained. These are specified as ratios of area under the load deflection curve to the area under the curve up to the first crack. With a 0.2-0.4in-wide crack, the shotcrete retains at least 60% of the first crack strength (Fig 3). For shotcrete of up to 3in-thick, 132-154lb of steel fiber/m3 is said to be more economical than welded wire mesh. Above this, welded wire mesh comes into its own.

Progress to date

The greater part of the tunnel is being excavated from the north portal in Kentucky where most muck disposal sites are located. Muck from the first 700ft advance from the Tennessee portals must be specially disposed of in Tennessee because the ground is sulphide bearing.

Tunnel excavation is by drill+blast using five Tamrock jumbos owned by SA Healy. “Rock penetration is averaging about 12ft/min in the best quality sandstone but wear of the drill bits and steels is high. The silicon content of the rock can be more than 90%.”

Three robotic shotcrete placing arms with pumps are employed on the project. One is a model TSA 12/4 Putzmeister machine imported from Germany through its Virginia-based distributor. A second, mounted on a Ford truck, was manufactured by Shotcrete Technologies of Colorado and the third was built by the contractor and mounted on a military 6x6 Reo truck. The latter two units are powered by Schwing Model 750 concrete pumps. All units use a 2in shotcrete hose to deliver about 20yd3/hr.

Excavation started in the top headings of both Kentucky portals in June 1991. By mid-March 1992, during the site visit, work was progressing from all four portals and the top heading was about 40% complete. Best production to date was 318ft/wk by all four top headings working a 24hr day, 5 day week with a half day Saturday for maintenance and to finish part-completed cycles. The new road is scheduled to be open in 1995, with demolition of the old road completed during 1996.

To date, progress, according to the contractor, has been influenced significantly by more frequent changes in the rock quality than originally predicted and by a greater

need for support than expected. While regular changes in support were anticipated, it was expected that the different types would extend for several cycles between differences in rock quality. “Changes in the support system are required as often as every round,” said Meldner. “We are also using more drill holes than expected to limit overbreak in this blocky rock.”

In accordance with the NATM concept, representatives from each of the parties involved meet regularly to decide the condition of the prevailing rock and agree on the necessary support. In the changeable conditions at Cumberland Gap the face inspection meetings take place every morning and after every blast. Their outcome is important since there is a significant difference in time and materials costs between the differing excavation and support cycles.

“It was the expected variability of the rock which initiated a pilot tunnel drive,” said Leary. “Cumberland Gap has the reputation of being one of the most pre-investigated tunnels in the country at present.” In addition to the pilot tunnel, a 2,000ft horizontal core was retrieved and four probes (two resistivity, one seismic and one radar) were included in the 1983 site investigation studies. Vertical cores were taken only at the portal areas.

The geotechnical analysis of the pilot tunnel records has provided information upon which changes in the rock quality in the main tunnel drive is predicted. In the same tunnel as the pilot, geological predictions between the two corelate well. Corelation across the 42ft pillar between the parallel headings, however, is said by the contractor to be not as good.

Thorough investigation of these potentially difficult geological conditions was undertaken to avoid the regular litigation that has plagued the USA tunneling industry over recent decades.

There have been several ideas introduced to the USA to combat this. One is the three-member Disputes Review Board concept, which wherever used, has operated successfully. However, its judgement is not final and there is still recourse to the courts.

In addition, the concept of partnering was introduced two years ago by the USA Army Corps of Engineers which faces about $1 billion in construction claims each year. Its aim is to break down the habitual adversarial attitudes between client and contractor and replace them with a sense of shared responsibility. The programme is built on a series of seminars conducted by a professional tutor unassociated with the industry at a venue away from the project environment and attended by equal numbers of senior representatives of the client, the consulting engineer and the contractor. The first seminar takes place soon after the contract is awarded.

Both the Disputes Review Board and the partnering concept are being implemented at Cumberland Gap and SA Healy has agreed to participate in a partnering exercise for its new contract in Texas for the DART Cityplace LRT running tunnels and underground station in Dallas (see page 19). The Cumberland Gap project is being carefully watched by the USA tunneling industry on both counts. n

TUNNEL DESIGN | GEOTECHNICAL ENGINEERING | CONSTRUCTION MANAGEMENT INSTRUMENTATION & MONITORING | WATERPROOFING & WATER CONTROL TUNNEL REHABILITATION | MINING SUPPORT SERVICES

www.dr-sauer.com Salzburg | London | Washington | Toronto | Tel Aviv

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The Dallas highway congestion solution that got away PROJECT OFFICE VISIT: APRIL 2003

T

win tunnels of three lanes each was a solution being developed as a congestion busting plan for one of the most notorious traffic bottlenecks on the freeways of Dallas, Texas. The west section of the I-635 Lyndon B Johnson (LBJ) ring road freeway on the north side of the city between its interchanges with the US-75, the Dallas North Tollway and the 35E radial freeways has one of the highest traffic volumes of the network (Fig 1). “At present this 9-miles carries more than 200,000 vehicles/day,” explained Matthew MacGregor, Planning and Design Manager for the LBJ project for TxDOT (the Texas Department of Transportation) when visited in 2003. “By 2007, when the new High 5 interchange with the US-75 freeway opens, this is expected to increase substantially. Future increased capacity on LBJ Freeway to the east of US-75 has been provided relatively easily as part of the 21-mile LBJ improvement project, but the central part of the west section is particularly problematic. There is nowhere to expand capacity on the surface. At the intersection with the Dallas North Tollway the 8-lane freeway is depressed in a cutting of about 25ft deep and there are no frontage roads on the surface. The only available space is underground.

We looked at elevated options but above all, we cannot afford to close capacity on the freeway during the upgrade. Underground is the only option.”

Having selected the underground option, one of the complications is incorporating the HOV or high occupancy vehicle lanes. As a major part of the upgrade, the plan is to direct HOV traffic into the new subsurface capacity and perhaps include a toll for single occupancy vehicles to use the tunnel lanes as an expressway. With absolutely no space for toll plazas, any suggested toll schemes would have to operate fully electronically.

as subconsultant to lead consultant HNTB Corporation for the full 21-mile upgrade, suggests two bored tunnels of 1.5 miles and 1.9 miles long (2.4km and 3km), traveling in-line and beneath the depressed highway and connecting either end to cut-and-cover transition zones to the surface. The tunnels would be designed to full 60 mile/ hr freeway traffic standards and comprise three-lanes in each 60ft wide profile at road deck level.

The ground beneath the depressed freeway comprises largely good quality Austin Formation limestone which is well known in Dallas as a favorable tunneling medium.

Existing tunnel projects in the Dallas area, including an access tunnel at Addison Airport designed by Lachel & Associates, and the underground Cityplace Station on the LRT designed by the Dr Sauer Corporation (see page 19), both illustrate the suitability of the Austin Formation limestone to the NATM or sequential method of tunnel design and construction. NATM is also recommended for the LBJ tunnels using roadheaders to advance the multidrift sequence of headings in the 1,570ft2 (146m2) cross section of each tunnel (Fig 2), with rockbolts, dowels, wire mesh and shotcrete as primary support. A PVC waterproof membrane system and a nominal 12in (300mm) reinforced in-situ concrete final lining is also included as part of the feasibility design.

From the cut-and-cover transition zones, the alignment would curve in to run inline beneath the depressed section of the LBJ. At the deepest level, beneath the Dallas North Tollway crossing, the tunnels will be about 100ft below surface at road level. This places the excavation at least one tunnel diameter into Section of LBJ Freeway with no continuous frontage roads where a single HOV/tolled express lane in each direction backs up daily along with all the traffic in peak hours

A feasibility study for the project completed by engineering firm Lachel & Associates of Golden, Colorado,

(Credit: David Woo, Staff Photographer, The Dallas Morning News)

Fig 1. Plan of Dallas area freeways

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good quality rock, beneath about 30ft or so of weathered limestone at the surface. The parallel tunnels will be separated by about one tunnel diameter or 60ft to create a tunnel corridor of some 180ft wide.

When first considered, it was planned that the LBJ upgrade would be completed at the same time the High 5 US-75 interchange in 2007. Funding constraints and other issues cancelled out this plan and even if construction was to start immediately, the LBJ upgrade could not be completed in time for the anticipated opening of the new interchange.

With the new interchange feeding more traffic onto the already overloaded freeway, getting this section upgraded as soon as possible is critical. Within funding constraints, that allow only 30-40% of identified projects for TxDOT to go ahead, the 9-mile west section LBJ Fig 2. Two new 3-lane NATM highway tunnels were at the heart of a Freeway upgrade, with a price estimate of $1 billion expansion program on the LBJ Freeway about $1 billion, is a priority. community in about September 2003 to invite requests To get the project completed as soon as possible, TxDOT for qualification. From an anticipated list of about is considering various procurement options including five teams, we would follow that with a request for an Exclusive Development Agreement (EDA). This is a proposals based on whichever procurement method the form of design-build contracting that could save several Board approves.” months on a normal design-bid-build process. Where standard design-build procurement of public works is not In the meantime, again to save time and after a successful legally permissible in Texas, the legislature has recently public hearing, TxDOT is preparing to complete additional ratified the EDA form of procurement and the Texas geotechnical investigations along the tunnel alignment Transportation Commission is watching progress of an and is expected to initiate an investment grade traffic and EDA road-building project before making a decision for revenue study to assess funding needs and prepare the the LBJ project. bond issue to raise cash flow. “With all these administrative issues taken care of, as soon as we award the contract, Meanwhile work continues to secure funding for the we can sell the bonds and get started straight away.” Civil project from various sources, including the FHWA excavation of the 1.5-mile and 1.9-mile long twin tunnels (Federal Highways Administration) and to acquire the within the proposed $1 billion budget is estimated at various environmental approvals. “These are complex between $140-170 million. Depending on the eventual programming issues that must be handled in a correct method of procurement selected, the project could be sequence for the project to move into detailed design and completed by between 2010 and 2015. construction stages as soon as possible,” said MacGregor.

“Not until we have cleared all the environmental and All change again funding issues can we go to the construction community In 2009, the estimated cost of the improvement project to bid the job.” had ballooned to $4 million to rebuild the existing eight lanes of the LBJ Freeway and add six new managed toll The process starts with a public hearing that was lanes. Two groups competed for the project, one opting scheduled for Spring 2003. As there is already an existing for a cantilevered style construction to add the new highway in the proposed project corridor a full EIS is not lanes above the existing depressed freeway from the required for application of FHWA funding. Instead, the sides, and the other following the proposed twin tunnel public hearing should result in a finding of no significant option with an option of one tunnel and three lanes on impact (FONSI). This alone will have saved an estimated the surface. The cantilevered style option was selected, two years or so on project development according to as its bid price was at more than a third of the cost to MacGregor. “We have been working on a project to ease taxpayers than the alternative tunnel-based option. The congestion on the LBJ freeway for more than 16 years,” he cantilever project was to start in 2010 and be completed said, “and we don’t expect any legal opposition to result by 2016, but that did not happen either. Only in August from the public hearing. With an approved FONSI we can 2019 did Pegasus Link Constructors, a group of Fluor then apply for Federal funding. In addition to the FHWA Enterprises, Balfour Beatty USA, and lead designer we will request funding from State, County, Regional and AECOM, secure a design-build contract with TxDOT to City sources as well as perhaps the North Texas Turnpike upgrade the offending section of freeway, without any Authority that operates the Dallas North Tollway, and underground works. The contract value at award was perhaps too from the NAFTA (North America Free Trade $1.7+ billion and the anticipated completion date is Agreement) budget since the IH-35E interchange at the now in 2024. n LBJ is a designated through route for trade between the USA and Mexico.

With decision on funding awaited and with another three months or so to clear all the remaining environmental approval issues, “we can expect to go the construction

TunnelTalk references •

Tunnel too rich for Dallas taxpayers - March 2009 35

Tributes Remembering Ray Henn

Remembering Ed Plotkin

A

s a native New Yorker, born in The Bronx, Ed Plotkin (1932-2022) was a natural go-to expert on all things tunneling and underground engineering in the USA industry. After earning his Bachelor’s Degree in Civil Engineering from CCNY in 1953, he went on to earn a Master’s Degree in Civil Engineering, also from CCNY in 1958, and an MBA in Engineering Management from the CUNY Baruch School of Business |in 1966.

His career experiences spanned all sectors of the industry working as a consulting engineer with DeLeuw Cather (now AECOM), where he was involved in the design of the Second Avenue Subway in New York in the 1970s; fulfilled the role of owner as Commissioner of Public Works for Westchester County in New York Edward Sheldon Plotkin State; and began his contracting career in New York, working with MacLean Grove among others, as Project Manager for the 63rd Street Subway and on the New York City potable water distribution Tunnel No 3 project. After retirement, he remained active in the industry, serving on Dispute Resolution Boards and speaking at many industry events and conferences. He also taught physics at Manhattan College and environmental science at Mercy College.

In 2010 Plotkin was the recipient of the UCA Lifetime Achievement Award and received an honorary doctorate from CCNY in 2019. n

F

ollowing a long career of more than 50 years in the underground construction industry, Ray Henn (1949-2022) held positions during his career from field engineer through superintendent, to construction manager and chief consultant on both direct-hire construction and construction management assignments on projects ranging in scope and value from $2 million to $1.8 billion.

Henn began his career as a surveyor with the Port Authority of New York & New Jersey before joining Morrison-Knudsen. In 1976, he joined Stone and Webster, where he served until 1995. He also worked for consultants Haley & Aldrich, Lyman Henn Dr Raymond W Henn and Brierley Associates before establishing his own company in 2015.

Henn was born and grew up in New York, attended New York City Community College and Queens College of the City University of New York. In 2005, Henn earned a PhD in Mining and Earth Systems Engineering from the Colorado School of Mines and became adjunct professor there in 2008. In recent years, he was active as a member of several Dispute Review Boards and served as an arbitrator and expert witness.

He was President of the AUA, American Underground Construction Association (now UCA of SME) from 2003-2005 (see page 64) and was recognised with the UCA Outstanding Individual Award in 2008. In addition to consulting and teaching, Henn is the author of three ASCE textbooks on grouting for underground construction. n

Remembering Dennis Lachel

I

n looking back through the case study projects of the Special USA Focus edition, we remember many good friends who have gone before us including Dennis Lachel who died in February 2006.

As well as an active member of the AUA, American Underground Construction Association at the time and now the UCA Underground Construction Association of the USA, Lachel was an uncompromising promoter of tunneling and a regular member of the USA delegation to the Annual General Assemblies of the ITA, International Tunnelling and Underground Space Association.

After establishing Lachel & Associates with partner Doug Hansen in 1976, Lachel and the company was involved in many national and international projects. Among the

Dennis Lachel and his wife Kathy (right) with TunnelTalk Editor Shani Wallis at the Sydney 2002 ITA Congress more extraordinary was design of the nuclear test tunnel facilities for the USA Department of Defense in Nevada and validating the closure and sealing of

the more than 180 nuclear test tunnels at the Semipalatinsk Nuclear Test Site in Kazakhstan. As Chair of the National Academy of Science USA National Committee on Tunneling Technology in the 1970s, he was instrumental in providing answers to key questions and issues important to national security.

In July 2004, Lachel merged his company with that of his long-time friend and colleague Conrad Felice to form Lachel Felice & Associates. The company missed the trusting and steadyhand style of Lachel’s management and continued his legacy of professionalism and commitment on company projects including the Whittier road and rail tunnel project in Alaska (see page 26) and the LBJ highway tunnels project in Dallas, Texas (see page 34). Lachel loved life and was never short of a hearty hello or time for a call. n

TunnelTalk references – Remembering USA industry leaders • • • • • • • • • • • • 36

Robert A. Pond, 1941 - 2008 Dr Ralph B Peck, 1912 - 2008 Robert J Jenny, 1932 - 2008 Donald Charles Rose, 1933 - 2008 Tor Brekke, 1934 - 2009 Thomas R Kuesel, 1926 - 2010 James Wilton, 1926 - 2010 Allan G Provost, 1936 - 2010 Joseph L Abbott, Died 2010 Drupad Batuklal (Dru) Desai, 1940 - 2010 William Kennedy, 1943 - 2012 Bill Quick, 1933 - 2013

• • • • • • • • • • • •

Dr Harvey Weston Parker, 1936 - 2020 James Monsees, Died 2019 Fred Benjamin Estep, 1938 - 2019 James Barbera, 1940 - 2019 David R Yankovich, 1953 - 2019 Dick Robbins, 1933 - 2019 Jack Feller, 1922 - 2019 Enrique Fernández González, 1958 - 2019 Walter Grantz, 1929 - 2018 George D Yoggy, 1937 - 2018 Prof Don U Deere, 1922 - 2018 James McKelvey, 1954 - 2015

CASE STUDY: For years Bostonians had paid one of the lowest rates for water and sewerage tax in the USA. This changed dramatically in the 19080s when rate payers of 43 towns and cities served by the Massachusetts Water Resources Authority (MWRA) contributed to a ten-year, $6.1 billion project to clean up severe pollution of Boston Harbor. After the TARP programme that prevented polluted water flowing from Chicago into Lake Michigan of the Great Lakes, the Boston Harbor project was one of the earliest and largest CSO pollution clean ups in the USA with many following on since, including Milwaukee.

Boston Harbor sparkles in wake of TBMs

SITE VISIT REPORT: OCTOBER 1989

B

oston, the capital city of the Commonwealth of Massachusetts, shares the dubious distinction, along with Chicago and Milwaukee, of being among those large US waterfront cities charged by the federal Environmental Protection Agency (EPA) to do something about the pollution caused by the discharge of insufficiently treated sewage into its water courses.

The harbor’s natural ability to dilute and dissolve the waste biologically has long since been overwhelmed.

Often it takes an individual or pressure group to prick the conscience of large, slow-moving public authorities and force them into taking action. In Boston’s case, an avid beach jogger sued the State agency responsible for water and sewer services. The Conservation Law Foundation in turn sued the Federal Environmental Protection Agency (EPA) for not enforcing the 1972 Federal Clean Water Act and the EPA responded by suing the State. A Federal District Court finding in May 1986 imposed an order by which the Massachusetts Water Resources Authority (MWRA) had to implement a program to rectify the situation by no later than 1999.

The scale of the work to comply with the court ruling to such a short deadline left no time to lose. Coordinated by its own program management division, the newly formed MWRA engaged Kaiser Engineers and its sub-consultants Howards Needles Tammen & Bergendoff (HNTB) and Geotest in April 1988 as its programme/construction

manager (P/CM) to implement the facilities plan studied in 1985-86 by Camp Dresser McKee (CDM).

Boston’s first sewage treatment plant was built on Nut Island in Quincy in 1952. As the region grew, a second plant was built at Deer Island in 1968. After primary screening, the waste is discharged through short outlets of little more than one mile long maximum. Discharge takes place once a day in the afternoon in the expectation that the ebbing tide will carry the waste out of the harbor.

Waste on the beaches proves that this is ill-founded.

Knowing the problems, CDM based the solution on better treatment and long-distance effluent outfall. To date, in the 1980s, there are about 14 long sea tunneled outfalls in operation worldwide, the largest currently under construction in Sydney, Australia.

In Boston, the CDM facilities plan has all treatment and discharge taking place on Deer Island with flow from Nut Island carried under the harbor to Deer Island in a 5 mile (7.6km) long tunnel. After primary and secondary treatment, the effluent will be discharged 8-10 miles out to sea beyond the harbor limits in about 110ft of water where the ecological balance of the ocean can naturally dilute and biodegrade the remaining waste (Fig 1).

When completed, the proposed Deer Island facility will have a peak capacity of more than 1,200 million gallons/ 37

day and will be the second largest such plant in the nation after then one in Chicago built in the 1950s.

CDM’s basic concept was accepted by the State and Federal Governments and the MWRA in May 1988. The next step was appointment of Metcalf & Eddy of Boston in August 1988 as the lead design engineer (LDE) responsible for conceptual design of all the facilities, including the tunnels and for the geotechnical investigation programs.

Rehabilitating the existing sewer network, parts of which are more than 100 years old, and eliminating the 87 combined sewer overflow points in the area, a major source of harbor pollution, is a separate but equally important matter. Once the CSO problem is also eradicated, the harbor will really start its own program of natural revival.

Because Metcalf & Eddy is more experienced in the design of wastewater treatment plants, including those in Chicago, San Francisco and Washington DC, it has engaged Mott Hay, the US subsidiary of British tunneling consultant Mott MacDonald (formerly Mott, Hay & Anderson), as a subconsultant for the tunneling works. Hager-Richter is the geotechnical subconsultant and Weston Geophysical is the team member responsible for geophysical surveys. British firm John Arthur & Associates is responsible for the multichannel digital seismic survey. Much of the tunnel muck is planned to be used to relandscape the site of and build bunds to shield the site and odors of the massive and much enlarged treatment plant on Deer Island.

The two major components of the scheme are the undersea tunnels. One is the 25,300ft (7.6km) Nut IslandDeer Island connection with a maximum and minimum flow of 360 million and 80 million gal/day. It is 13ft 4in (4m) o.d. and finished to 11ft (3.5m) i.d. with an insitu concrete lining. It has a 320ft (97.5m) deep shaft at Deer Island and another at 245ft (75m) deep at Nut Island with inner diameters of between 11ft and 16ft (3.35m-5m). A 90ft x 40ft x 35ft-deep (27m x 12m x 11m) surge overflow tank is also required.

Ocean outfall tunnel

The 49,000ft long x 24ft 6in i.d. (15.4km x 7.5m) ocean outfall tunnel, its proposed 30ft diameter x 400ft (9.1m x 122m) egress shaft and its discharge diffusers at the far end, is designed for a peak flow of 1,260 million gal/day and an average flow of 500 million gal/day. The general distance and location of the outfall was fixed by the EPA and a final site is currently being defined. The original facilities study calls for 80 x 2.5ft (76cm) diameter diffuser risers planned over the final 6,600ft (2km) length of the tunnel. “These risers are estimated at about $1 million each and studies are under way at the Georgia Technical University to determine if they can be reduced to 55,” said Lawrence Williamson, Senior Design Manager for the MWRA’s program management division (PMD).

Besides the tight court-ordered deadlines, the construction schedule is severely limited by logistics. With no room to use Nut Island as the working access for the inter-island tunnel, all tunneling must start on Deer Island.

This, together with the new treatment facility works, as well as having to keep the existing facility in operation, will make Deer Island an extremely congested construction site when work starts.

A narrow but natural causeway joins Deer Island to the streets of Winthrop town on the mainland. But, as this 38

causeway is unsuitable as the main access to the site, all construction materials and equipment and 50% of the workforce, which will peak at 2,400 workers/day, will have to be transported to and from the Island by ferry and barge. The remaining 50% of the workforce will be bussed through Winthrop.

To meet the imposed deadlines, the project’s schedule is having to be fast-tracked wherever possible. For this reason, detail designers for the two tunnels, which will also prepare the bid documents, were engaged before the lead designer had completed its conceptual design. In February 1989, Sverdrup, leading a group of specialist firms, was engaged as the project design engineer (PDE) for the interisland tunnel and Parsons Brinckerhoff Quade & Douglas is leader of the group designing the ocean outfall.

To facilitate communications between the various levels of design and planning on this enormous and complex project, MWRA has installed a uniform computer-aided drafting and design (CADD) system. It has bought and installed, on a loan basis, all the hardware required and provided the software in each of the associated design offices. “We have chosen the McDonnell Douglas GDS CADD system,” said Williamson “because it provides the best 3D facility and has good database cooperation. Some 85% of estimating will also be accomplished on the system.”

According to the court order, both tunnels must be in operation by mid-1995 with the designs completed by December 1989 and the contracts tendered for and awarded by January 1991. With only five years maximum to complete the tunnels and with no possibility of opening up multiple headings, this is a job for full face TBMs. Fortunately, Boston is built on a foundation of good quality sedimentary and volcanic rock which is well documented and highly suited to the application of TBMs. Drill+blast or a roadheader may have to be used at the diffuser end of the outfall where the tunnel must gradually taper for hydraulic operation for the diffusers. Not only will TBMs be faster, they will also be cheaper in this application.

“We will be looking for TBM progress rates of about 100ft (30.5m)/24h working day to meet the construction schedule,”’ said Birger Schmidt, Parsons Brinckerhoff’s Director of Geotechnical Services.

Undersea sewers

Most of the previous tunnels in Boston have been excavated by drill+blast. There are already two undersea sewer tunnel links from the mainland to Deer Island built in the early and mid 1950s. The only TBM project in Boston to date is the 6 mile x 10ft i.d. Dorchester water supply tunnel excavated in 1968-74. Unfortunately, the TBM completed only 3,800ft before having to be removed but this was early days for full face TBM tunneling and the technology has greatly improved since. The technique has not been used in Boston in the meantime because the tunnels required have either been too short, too small in diameter or of the wrong profile for cost-effective TBM application.

To investigate further the nature of the rock on the proposed new tunnel alignments, extensive geotechnical surveys have been undertaken. Warren George completed a borehole contract in 1988, taking 25 cores from the outfall alignment and four on the inter-island line. The program also called for 215 miles and 95 miles of seismic reflection and refraction profiling on the tunnels respectively. Sidescan sonar and magnetic data were gathered for an area of 25 mile2 in the vicinity of the outfall tunnel and diffuser

Right: Fig 1. Plan of the cleanup infrastructure Below: Fig 2. Inter-island tunnel to be deep and doglegged to avoid a known depression and weathered fault zones; Fig 3. The 15.4km length x 8m o.d. undersea outfall is a TBM driven operation

section. A further program of surveys, including 31 borings along the outfall and 16 along the inter-island tunnel, was carried out by Warren George in Summer 1989 to allow the detail designers to fix the final alignments. “The 1989 geotechnical study alone cost about $10 million,” remarked Brian Van Weele, Project Manager for Parsons Brinckerhoff.

“The total cost of exploration is more than the two final design contracts combined.”

From data already available it is possible to predict that some 85% of both tunnels should be driven through good quality argillite, a slightly metamorphosed mudstone or siltstone with an average compressive strength of 106MPa. The rest is in diabase igneous materials which intrude through the formation as dykes and sills. The RQD (rock quality designation) is generally good but there is some jointing and faulting. Compressive strengths of the diabase can be up to 334MPa but considerably less in altered and fractured fault zones. Average strength of diabase samples is 75-135MPa with an average hardness of 98MPa.

Kaolinite strata

“A concern for TBM tunneling is the presence of kaolinite which, while tight to water, is a soft material which would not resist the pressures necessary to thrust a TBM forward,” said Williamson. From experience, these areas of altered kaolinite-based strata can be from 10ft to 100ft or more in thickness and more than 300ft deep. Kaolinite and weathered rock zones are expected to be more prevalent on the inter-island tunnel than on the outfall. Its alignment will be dog-legged to avoid identified adverse features and a deep depression in the bedrock.

Support in previous drill+blast tunnels has been remarkably light, with as little as 10% to 35% of a tunnel

length requiring steel arch support. This is expected to be less in a TBM driven tunnel where disturbance of the surrounding rock is less. However, TBM specifications will require the ability to install rock bolts or steel rings close to the face.

Water ingress

Water ingress is not expected to be a serious problem except where extensive breccia is found in fault zones.

Both tunnels will be driven on a slight 0.05% to 0.3% uphill gradient to drain any water inflows. “The gradient will also assist in the final operations since the tunnels, with a design life of 100 years, may be drained for inspection probably after 30 to 60 years in service,” said John Moss, Project Director for Mott Hay. Water ingress during excavation is expected to be greater in the inter-island tunnel at about 1,000-18,000 gal/min over the full 7.6km length. Systematic probing will be carried out on both tunnel drives. Design specifications for the TBMs will call for the ability to accommodate the drilling equipment. “Waterproof rather than splashproof electric systems will also be a TBM specification,” said Moss.

For hydraulic purposes, both tunnels require an inner concrete lining. Although the tunnel will be under hydraulic pressures, the 1ft-thick lining will be of largely unreinforced concrete. Concrete durability rather than strength is a more important design factor. The inner lining must not only withstand the corrosive nature of effluent but also the rigors of periodic saltwater infiltration on the outfall tunnel.

There is time in the construction phase for the concrete to be cast as a separate operation on the shorter inter39

island tunnel, but it will have to be placed concurrently with TBM excavation in the outfall.

Concurrent concrete casting could be achieved with the extruded concrete method developed by Hochtief in West Germany and used on the under-river drives for the Lyon Metro, or the TBM could be equipped to erect precast concrete segments like the Robbins TBM being used on the Sydney outfalls. “At present, the preferred design method appears to be a precast invert with an in-situ arch following some distance behind,” said Williamson.

In any kaolinite weak zones, precast concrete segments would be required for support and as a TBM thrust block.

Again, because of logistics, the tunnel contractors will have to buy their concrete supplies from a batching plant established on Deer Island by the client as there is no way of getting concrete to the island from other suppliers.

The topography of the seabed determines the depth of the tunnels at ideally 3.5 times the diameter or 70ft (21m) into good solid rock. Because of the mountainous nature of the harbor floor, the 100ft of till and the 10ft to 15ft of weathered rock above the bedrock, the inter-island tunnel will be on average 225ft to 300ft below sea level and the outfall 350ft to 375ft below sea level.

“Pressure tunnels in rock with unreinforced inner linings have been known to burst,” said Moss. “The Dorchester tunnel here in Boston is an example. The design for these tunnels allows for 70ft between the top of the tunnel and the rock interface but it would not cause a heavy financial or time penalty to go deeper if necessary.”

Detailed design of the tunnel work is to be finalized by December 1989 and while attempts are being made to better them, the 54-month outfall construction contract must be awarded by January 1991 and the 45-month interisland tunnel contract by April 1991. Although there are 75 construction contracts on the entire project, both tunnels and their associated shafts and the risers are planned to be let as single contracts. For the estimated $100 million inter-island contract this poses no great problem, but for the estimated $400 million outfall, this constitutes a very large contract involving a great deal of risk for any one contractor, particularly in connecting the tunnel with the pre-drilled riser shafts. For this reason, a multiple contract option is under review.

Two contracts

“It is better for the MWRA to let these operations as one contract,” said Van Weele, “because the one contractor is then responsible for each stage. If each stage was accomplished by a different contractor, there is room for one to blame the other for any problems with the connection, for example, a situation which would be very difficult to sort out. But from a contracting point of view, it may be easier for bidding and scheduling purposes, if the outfall shaft and tunnel, and the fabrication and installation of the risers and diffusers, were let as two separate contracts.”

The size of one $400 million outfall contract would also limit the potential within the construction industry to handle it. Very few contractors would be able to raise the necessary bonding which, on this job could be about 75% of the contract price. Even if the larger USA contractors grouped together in joint venture, it is unlikely that there would be more than two all-American bids.

Shafts on both contracts are estimated as lump sum items in the tender documents and the tunnels are planned to be bid on a unit cost/ft basis. “The method of shaft excavation and the risks involved will be the contractor’s choice,” said Hugh Caspe, Project Director for Sverdrup, “but ground freezing or slurry diaphragm walling will be required through the upper strata which have a lense of fine waterbearing sand. The contractor will also fix the working o.d. of the shaft and a 1% tolerance on deviation has been set.”

The contracts themselves are quite unusual in that UTRC (Underground Technology Research Council) contractual recommendations are planned to be followed. “As a base line, the geotechnical data report is included in the contract together with its official interpretation and geotechnical design summary report,” said Caspe. “The contractor’s bid documents are to be placed in escrow (held by a third party) and, while there are changed condition clauses, there will be a dispute review board to avoid litigation.”

Fast tracking

To save time, there was the possibility that the client would buy the two TBMs required for the job, thus allowing the machines to be ordered and partially built before the contract was tendered and let. This idea was since dropped as it would have placed too much responsibility on the client. “The outfall TBM has a 27ft (8m) o.d.,” said Moss. “The inter-island TBM o.d. is 4m.

TunnelTalk references There is a one-year allowance in the schedule • Hydroshield and extruded lining usage in Lyon - Jan 2013 for building and commissioning each TBM.” • Potomac River CSO approved in Washington DC - April 2020 Now, before construction begins, MWRA must • Narragansett Pawtucket CSO contract award - January 2021 raise the required $7,500 million in bonds to • One TBM for two-diameter Mill Creek alignment - October 2019 finance the work. This will be paid back by • CSO mega-project prompts St Louis expansion - March 2014 water rate increases of $45 to $75 over the next ten years. Rates will increase from the present • Cleveland progressing its CSO network - September 2020 $350-400/year in 1989 to $1,000 or more in • CSO solution goes underground in Louisville - November 2019 1999. The inter-island tunnel is expected to be • Challenges overcome as Kentucky CSO completes - October 2020 completed by December 1994 and the outfall tunnel in service by July 1995.

• OARS shaft-sinking challenges in Columbus, Ohio - October 2011

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Robbins TBM sets records in Indianapolis - August 2014

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DigIndy progresses to final bore - December 2020

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TBMs+conveyors - speedy combination in Indianapolis - April 2015

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Cincinnati plans deep CSO program - November 2010

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Mobilizing for the Los Angeles outfall drive - March 2021

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Set up for Detroit’s second effluent outfall - April 2009

Contract award and progress

In early January 1994, the project celebrated an advance of 530ft (161m) in a week by the 26ft 8in (8m) diameter Robbins TBM excavating the 9.5 mile (15km) segmentally lined ocean outfall. This is the best advance achieved by the TBM in some months. After

a troubled start in July 1992, the Kiewit/Guy F Atkinson/ Kenny JV, awarded the $202 million bid price contract in early 1992, had advanced the TBM about 15,550ft (4.7km) into the 15km long drive by mid-January 1994 and was running a projected 10 months behind schedule.

The double shield telescopic TBM was allowing concurrent boring and building of the segmental lining of six uniform trapezoidal segments in each 5ft (1.5m) wide ring.

Designed by Mayreder Consult of Austria, the segments are fitted with a neoprene gasket and pea gravel is blown in behind the lining through the segment handling holes to fill the 3in (750mm) annulus between the lining and the argillite rock and consolidated with cement grout.

Muck haulage is via continuous conveyor supplied by Long-Airdox and a Trellex Flexowell vertical shaft conveyor from Lake Shore Industries. Running at about 600ft/min, the system has a capacity of 900 tonne/hr.

Using this system, tunnel advance was programmed by the JV at about 100ft (30m)/day or 600ft (180m)/week working three shifts/24hr day, six days/week. The average, however, has been well below that at about 65-70ft (2021m)/day. The best daily advance was 140ft (42m) recorded in June 1993. The best week to date is 619ft (188m), and the best month is 1,826ft (555m) in July 1993.

Troubles started during installation of the 140ft (42m) deep diaphragm wall and excavation of the 420ft deep x 30ft diameter (127m x 9m) access shaft. Both operations, which were in the hands of separate subcontractors, fell behind time and the shaft had to be completed by the JV itself. During assembly, the TBM’s main bearing was found damaged in transit and a replacement was required. During the launch, the thrust ram and grippers were damaged causing another delay. Further delays during 1993 included a three-week downtime to improve the water resistance of the TBM’s electrical systems. Another 10 days were needed to replace the main bearing seal, and a crack in a gripper took one month to repair.

The latest loss of six weeks occurred in November/ December 1993 when the TBM entered a zone where two faults in the argillite intersect. In the blocky material, loose rock fell from the face, side walls and crown creating large voids and rendering the tunneling system ineffective.

These voids, one of which was 25ft x 35ft x 25ft high (7.5m x 10m x 7.5m), had to be backfilled with concrete before tunneling could progress. This is the first of three zones of difficult geology identified along the outfall alignment. Water ingress was a major concern on the two undersea drives and contract documents specified a pumping capacity of 10,000 gal/min on the outfall and 3,200 gal/min on the inter-island contract.

Inter-island connection

Steady progress of about 450ft (137m)/week was being achieved on the inter-island undersea TBM drive. Under a $73 million contract, the S A Healy/Modern Continental JV is using a 13ft 8in (4m) o.d. refurbished Robbins TBM to excavate the 5 mile long (8km) tunnel to convey raw sewage from Nut Island to the new treatment plant on Deer Island.

After sinking the 290ft deep x 23ft o.d. Deer Island shaft, the TBM was launched in August 1992 and was about 15,350ft (4.6km) into the 8km drive by mid-January 1994.

This drive, predominantly through argillite, is supported

Site of the inter-island access working shaft

as required using rockbolts, mine mats, steel sets and shotcrete and will be finished to an 11.5ft (3.5m) i.d. with an in-situ concrete lining. Equipment for dry mix shotcreting is assembled on a flat car which is taken into the tunnel as needed. Muck away is in 6yd3 muck cars and lifted out of the shaft on a Trellex Flexowell vertical conveyor with a maximum capacity of 500 tonne/hr.

With another 11,000ft (3.3km) to go, the inter-island TBM is expected to break into the Nut Island shaft in June 1994.

Due to earlier delays on the shaft sinking operation and various other factors, this tunnel is also running behind schedule. It is now expected to finish about six months later than the original program which was based on an average of 12ft/day, working three shifts/day.

Elsewhere on this $6.1 billion project for the Massachusetts Water Resources Authority (MWRA), the 55 risers over the last 1.25 miles of the outfall are complete. The 30in diameter (760mm) pipes were installed under a separate $77 million contract by the Cashman/Interbeton JV. The risers lie under about 105ft of water and pass another 250ft (76m) down to tunnel level.

The first phase of the treatment plant upgrade on Deer Island is on schedule to meet the court deadline of July 1994. Given the delays, the inter-island and outfall tunnels are projected to be completed in July 1995 and March 1996 missing their December 1994 and July 1995 courtordered commissioning dates respectively. To facilitate the tunneling program, the outfall contractor is considering using the TBM, instead of the drill+blast plan, to excavate the last 1.5 miles (2.5km) through the diffuser section, and achieve the gradual reduction in diameter for proper operation of the diffuser with in-situ concrete. The outfall TBM is now scheduled to finish its task in June 1995 and connection to each of the 55 risers would follow.

“There have been problems on the two undersea tunneling contracts,” said Mr Walter Armstrong, Director of the Programme Management Division for the MWRA, “but we feel we have now turned the corner. We are at the peak of the construction phase on Deer Island and are working with the contractors to try and recover some of the time lost.”

One of the greatest problems facing contractors was that Deer Island, as the main construction site, become a remote and extremely congested workplace where morale became difficult to maintain. According to Armstrong, about 3,000 people were working on Deer Island, and expenditure on the project was at its peak at about $3 million/day. n 41

Milwaukee builds-in a spring clean SITE VISIT REPORT: MAY 1985

M

ilwaukee, on the Great Lakes of USA, is one of the heaviest polluters of Lake Michigan, with some 500 overflow points discharging into its waterway about 50 times a year. In the early 1960s,

pollution of the Great Lakes became a serious problem and the Federal Government through its Environment Protection Agency (EPA) was forced to take action. In 1972, the Clean Water Act which set a national goal for ‘fishable and swimmable water’ for sewage treatment was passed and presented many large industrial cities with a sobering ultimatum: Do something about controlling the overflow of combined raw sewage and storm water into rivers and other waterways or pay heavy penalties.

Chicago was one of the first cities compelled by the EPA via a Federal Supreme Court order to deal with its sewer overflow problem. This resulted in the massive tunnel and reservoir plan (TARP), construction which started in 1976 and the mainstream portion of which has been in operation for more than a year. In 1977 Milwaukee also received a State/EPA direction to take immediate action and eliminate its surge overflow problem by 1990. This initiated the $1.65 billion Water Pollution Abatement Program (WPAP) in 1986 prices, excluding the cost of borrowed monies. It is the largest public works project in the history of the State of Wisconsin and one of the largest construction program in the USA presently.

Milwaukee Metropolitan Sewerage District (MMSD) owns and operates some 235 miles (378km) of main interceptor sewers which are fed by more than 2,200 miles (3,540km) of smaller local sewers owned and operated by municipalities served by the District. As client for the WPAP, MMSD took the fundamental decision at the outset to adopt a program management concept rather than increasing its permanent staff to handle the project in-house. This is believed to be the first time that planning, design and management of a major sewer project in the USA has been managed in this way. The concept is adopted more usually for mass transit projects.

From eight finalists, the contract was awarded in 1977 to CH2M Hill of Corvallis, Oregon, as leader of an original consortium of six associates. The Milwaukee WPAP is the largest project the firm has ever managed. To administer the project, MMSD augmented its staff by 20 engineers.

Executive Director of the program for MMSD is Patrick Marchese and Director of the PMO and Marchese’s counterpart is Henry Padgham, Vice-President of CH2M Hill.

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By adopting this concept, the undivided attention of CH2M Hill and the PMO completed the planning stage of the WPAP in less than three years. Planning of other similar scale projects has taken much longer, five to seven years in some cases, when handled in-house by the owner. This expedient start paid off handsomely when it came to financing the project. The District received $50 million in Federal and State grants, which may not otherwise have been available, and it allowed an earlier start of construction saving an estimated $390 million in inflation costs and long term professional service fees.

Scope of the work

Of some 40 miles (64km) of new sewers to intercept the offending overflow discharge points, the largest, 30ft (9.14m) in diameter, and deepest tunnels, 300ft (91m) below the surface, will act as storage facilities until the system can cope with the excess volume. Under normal conditions, flow will be conducted to the Jones Island treatment plant through the shallower smaller diameter network. Only when excess flow overloads this network (about 50 days annually) will the deep reservoir tunnels come into operation. A sophisticated and complex system of automated, computer-controlled valves, gates and telemetry will co-ordinate the correct use of the system.

Cost of this 19-year masterplan was estimated at $1,692 million in 1980 prices when accepted in June 1980. Half of this is being met through Federal and State Government grants and the remaining 50% has to be raised by MMSD by the issue of general obligation capital purpose bonds and secondly by levying a regulated temporary increase in direct property tax. The sewer tax, $3.42/$1,000 of equalized valuation, will not increase if all goes according to plan, and will drop to nearly zero in 1996.

Due to time and budgeting constraints, the program managers found that much of the construction work had to begin before the design was completed. Once the financing arrangements were finalized, construction started with the driving of two new 6,200ft long x 10.75ft (2km x 3.3m) diameter twin siphon sewers under the Harbor and Milwaukee River to link most of the city interceptor network with the Jones Island plant. This $17.6 million contract was won by a Harrison Western led JV in 1983. When complete, in mid 1986, it will replace the nearby 69-year-old siphon.

Work also started on the extensive Jones Island expansion works which constitute the most expensive part of the program. Several shallow relief sewer

contracts were also let. Most of these are soft ground tunnel drives below the water table. Compressed air has been used on many with a primary lining of ribs and lagging followed by a secondary in-situ concrete lining.

Some have been pipejacking operations and precast concrete segments have been used. About 75% of these smaller sewer drives were complete at the end of 1985. During a visit to the project in 1985, the planning stage was complete and 80% of the design phase was finalized and construction was 25% complete with another 25% awarded.

The most remarkable facts about the entire program are that it is running to schedule and is running under the original 1980 cost estimate by more than 10%. This is attributable not only to tight control over the project but also to the highly competitive climate of the USA tunneling industry. As Henry Padgham explained: “Contracts are

awarded to the lowest responsive, responsible bidder, and these have been up to 15% less than our estimates.”

At present the program is forecast to cost $2,100 million, $350 million for consulting and project management fees and some $450 estimated for the cost of borrowed money.

Construction costs are recalibrated once every year to allow for future inflation at 8% annually. “Construction will peak late in 1986 when some 248 of the 386 contracts to finish the project will be complete or underway,” said Padgham (Fig 2). “About 60 different contractors will be engaged at that time and payments to contractors over the three main construction years will total approximately $1 million/day.”

During the project visit, a tour was organised to two current underground contracts - the deep-level pumping station and its associated shafts on Jones Island and a section of the Crosstown deep level large-diameter reservoir tunnel.

Mixed fortunes for shaft freezers

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.

WPAP 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, as Cementation, contractor of perhaps the most important shaft sinking contract of the program, found out.

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

Installation of the freeze system for the screening shaft

the Area Manager for Cementation from UK 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 ground is extremely hard and has to be picked out using hand machines. 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 the unfrozen core of the shaft.”

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

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Dry run to ensure the mini excavator would lower down the concrete lined shaft to excavate the connection tunnel

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.”

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.

Triple deck platform for concrete lining work

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 wandered 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.

They are 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 hand machines.

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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.

Bottoms up

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 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). The pumping chamber will then be excavated using drill+blast and the connecting tunnel from the screening shaft to the pumping station will be driven. Completion of the contract remained on schedule for later in 1986.

New challenge for TARP TBM in Milwaukee

T

he first reservoir tunnel contract to be let for the WPAP project was the 21,292ft (6.5km) length on the Crosstown interceptor from and including Stadium access shaft to the Cementation inline pumping station at Jones Island. It is designed as a 30ft (9.15m) diameter tunnel some 300ft (91.5m) below the surface in dolomitic limestone with a compressive strength ranging from 15,000 to 22,000psi and a RQD (rock quality designation) of 95 to 100%. For this and all the deep level tunnels in Milwaukee, fullface TBM excavation has been specified and if rock conditions are as competent as expected, and the Wisconsin Department of Natural Resources concurs, they will remain unlined. If not, a separate in-situ concrete lining contract will be let after excavation.

Tenders for this contract, estimated by the Engineer at $55 million were invited in December 1983. Of eight competing groups, a bid by the consortium led by Dillingham was lowest at $42 million. The tender, based on a similar operation as that used by the Ball/Healy/Horn JV for its $94 million tunnel contract for the TARP project in Chicago in 1977, was accepted and notice to proceed was granted in April 1984. S A Healy, Grow Tunneling and C Dew & Sons are partners with Dillingham in Milwaukee. Dillingham bought out the Ball company in 1969, retaining the Ball name until May 1981, and Healy was a major JV partner in Chicago. As a result the same 32ft 4in (9.86m) diameter Robbins TBM as used in Chicago, with the same back-up, mucking and shaft hauling equipment, is being used in Milwaukee.

“Besides, cutter wear is not expected to be much different on the Milwaukee drive,” said Roger Bailey, Site Manager for Dillingham. “The limestone is more fractured with many clay partings and will be easier to bore than the harder more competent dolomitic limestone rock in Chicago. We anticipate a progress rate of between 75ft and 85ft (2326m)/three 8hr shifts/day here in Milwaukee.”

Work on site started 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.

Freezing but fine

For the second reception shaft, Geofreeze was subcontracted to sink a freeze shaft using a mobile freeze Dillingham TBM working shaft with rota-dumper on the right

After driving 4 miles (6.5km) in Chicago, the 650 tonne TBM was refurbished by Dilllingham technicians at its workshop in Plainfield, Illinois. The cutterhead was equipped with 64 x 15.5in disc cutters for the Chicago jpb and these gave a 40-60 linear feet (12-18m) advance before needing to be changed. During refurbishment, Dillingham did consider replacing these with 17in discs to extend cutter life but the costs of modifying the cutter saddles on the head almost matched the likely amount to be saved in cutter wear.

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

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 TBM launch chamber fitted with starter walls and an extra 80ft (24m) muck hopper pit below the invert in the shaft area was complete. A 2-boom Gardner-Denver Airtrack pneumatic drilling jumbo and Tovex explosives from Du Pont were used to excavate the chambers. Top heading and benching was applied in the large TBM launch chamber.

While this work was going on, the TBM, which arrived on site in colour coded and numbered pieces, was assembled. “We laid all the pieces out in order under the bridge and had it assembled within six weeks,” said Graham. Robbins technicians Pete Plypic, Garry Richards and Pat Taylor were on hand at different times to give advice on many aspects of the machine’s operation.

the 40,000 to 50,000lb (18,150 to 22,700kg)/cutter loads. A water bath dust filter is also housed on the trailing back­up.

Streamline mucking

A smooth, efficient, reliable mucking out system is based on a continuous mining shaft-hauling system. Each muck train, consisting of eight 25yd3 (19m3) cars hauled by a 35 tonne loco, pulls into a rotary dumper where each car is up turned through 180° and emptied into the lower muck hopper which holds in excess of a full train load.

From here, muck is batched into one of two 15yd3 shaft buckets which are operated in contrary motion from a single cabin drum 75ft above the top of the shaft. This shaft system runs non-stop at a maximum speed of 250ft/ min. At the TBM, empty cars are automatically lifted one at a time from the incoming track and onto the outgoing track over which the 85ft secondary conveyor loads the individual cars.

A systematic rockbolting pattern has been specified for immediate rock support. Five 10ft long grade 60 steel Dywidag rockbolts encapsulated with Du Pont’s Fastlock resin will be installed on 5ft centers across the crown with two 12ft long bolts either side, explained Dwight Chewning, Project Engineer. Bolt holes will be drilled with two Tamrock air drills located on the back-up trailers. With these, the 1.5in cross bits will penetrate the limestone at 6ft/min. In addition, the contract requires availability of 50 circular steel arches to be inserted as directed by the Resident Engineer if and where necessary.

If the tunnel is to remain unlined as originally intended, it will be rendered watertight by grout injection. This will be carried out from a grouting jumbo gantry about 1,000ft (305m) behind the TBM. On this, a Tamrock E410 pneumatic drifter mounted on a boom with a 4ft feed extension will drill the 10ft (3m) to 12ft long grout holes.

Water ingress after grouting is expected to be about 250gal (946litre)/min over the total length.

During the site visit, the TBM had been assembled in the launch chamber and was about to start on its 6.5km In August 1985, the TBM was lowered down the access long journey. Since then, Dillingham’s progress rates had shaft and after boring 136m, it was halted for assembly exceeded at least once, each of the records held for 32ft of the 14 back-up gantries. These carry two transformers diameter machines and larger. The best day was in excess which lower the 13,200V electric power supply down to of 146ft (44.5m); the best week was in excess of 600ft the 480V required to drive the 2,400hp TBM and apply (183m); and the best month, more than 2,024ft (617m). The highest volume excavated in a 24hr period is 4,300yd3 (3,287m3). Dillingham anticipated TunnelTalk references completing the contract in February 1988, four months earlier than scheduled. “Should • VIDEO: Northern Boulevard ground-freezing support - April 2013 we manage to achieve this, it will be a credit • Ground freezing collapse raises queries and concerns - August 2017 to the combined efforts of our whole team,” • Slurry TBMs and ground freezing for East Side Access - March 2011 attributes Bailey. n 46

San Diego effluent management SITE VISIT REPORT: MAY 1997

Driving a sub-sea outfall in difficult ground Mitsubishi EPBM and its Boretec back-up fully assembled and site tested with the Pacific Ocean behind and before being lowered into the 200ft deep access shaft

B

oulders, high hydrostatic pressures and abrasive alluvial materials were the treacherous conditions awaiting TBM tunnelers on the South Bay ocean outfall project in San Diego in the mid-1990s. Added to this was the high probability of seismic activity during construction and through the facility’s design life, ranking this project as among the most difficult subaqueous tunnels to be driven in the 1990s, along with the St Clair railway tunnel in Canada and the Storebaelt railway project in Denmark.

At nearly 3.5 miles long, the 11ft i.d. machine driven tunnel passes through a complex mix of alluvial deposits washed down by the Tijuana River over the ages. The composition of the seabed at the mouth of the estuary ranges from fine silts and clays to granular sands and loose alluvial gravels in which sizeable cobbles and large boulders are anticipated. From a 200ft deep shaft set about 1 mile back from the shoreline, the tunnel has been designed to pass through the San Diego Formation at up to 158ft below the seabed and about 230ft below sea level (Figs 1 and 2).

The alluvial material is highly abrasive and it is expected that at least two complete changes of cutterhead tools will be needed. The contract specifies four mandatory man entry inspections in areas where conditions will allow safe intervention under compressed air pressures of less than 3 bar.

The first possible chance for an air assisted man entry, however, is in Reach 2 at about 3,000ft from the shaft.

Figs 1 and 2. Plan and geological section of the 3.5 mile long South Bay undersea outfall, which passes through complex alluvial materials beneath the floor of the Pacific Ocean

Intensive site investigation studies and a comprehensive geological report prepared by project designer Parsons Engineering Science indicate that, as far as can be predicted, the tunnel will pass through four reaches of quite different geology. Reaches 1 and 3 are said to lie in porous granular sandy and gravelly material in which the full 7 bar hydrostatic pressure of the sea must be expected. Reaches 2 and 4 are anticipated to be in a more competent, less permeable silty material under more moderate pressure.

In the porous, gravelly conditions of reaches 1 and 3, there can be no man entry into the TBM plenum, or excavation chamber, without the assistance of ground freezing. In reaches 2 and 4, safe man entry is expected to require a degree of compressed air to help hold the face.

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The porous sandy gravels of Reach 1 deny man entry without the application of ground freezing. The same situation then occurs in reaches 3 and 4, where tunneling must continue for some 3,700ft through the porous sands and gravels of Reach 3 before inspection of the cutterhead is possible again in the more competent silts and clays of Reach 4.

buried pipeline in order to pass under the nature reserve established to protect the ecology of the Tijuana River valley and its estuary. The riser shaft and its seabed extension, as opposed to a longer tunnel with a series of individual risers to the seabed, is required because the geology suitable for tunneling dips away sharply at the transition (Fig 1).

To manage excavation of this difficult drive, Parsons Engineering specified the use of either an EPBM or a slurry machine. It had to be purpose built to cope with pressures of up to 7 bar minimum and with boulders up to 3ft in diameter. It also had to be able to carry out forward probe drilling and set up ground freezing around the machine in case it should be needed. The machine also had to comply with the strict health and safety standards required for tunneling through an active seismic zone. It had to be fitted with gas monitors, automatic cut outs and had to be explosion proof.

“Although far from being ideal, the San Diego Formation is the most favourable geological formation for tunneling,” explained Greg Colzani, Chief Resident Engineer for Sverdrup/lCF Kaiser Engineers, the Construction Management JV. “At about 6km, this gives way to the middle Pleistocene gravels, which are highly porous, and to the upper Holocene sediments, which are little more than sands and alluvial muds. We had to rise to the seabed to continue the outfall as a buried pipeline to reach the appointed site of discharge.”

Behind the machine, Parsons allowed the contractor a choice of either a two-pass lining or a highly specified onepass precast concrete bolted and gasketed segmental lining as commonly used in Europe and Japan. Since a bolted and gasketed system was specified as the primary lining of a two-pass system, it was expected that the onepass system would be chosen.

Contract award

Two JVs submitted bids. The difficulty of the drive was well appreciated and both JVs included an experienced pressurised TBM tunneling partner from Japan. In September 1995 the contract was awarded to Traylor/ Obayashi as the lower of the two bids at $88.3 million.

Kajima/Dillingham in competition was within 5-7%, or $5 million, of that bid and both were very close to the Engineer’s Estimate of about $90 million.

The 3.5 mile long outfall with a separate $36 million marine works contract to install the 4,670ft seabed extension from the riser shaft and the two tapered diffuser legs, was chosen in opposition to a seabed and

F

or decades, untreated sewage and wastewater has been flowing north from Tijuan in Mexico to the USA via the Tijuana River and other north flowing canyon and gully waterways. By the late 1990s, Tijuana was a city of more than 1 million and, although sewage treatment plants and pumping stations have been built over the years, overflow of wastewater still made its way north of the border, causing environmental and health threats to communities in the South Bay area. Since the early 1980s, some of the most polluted channels had been diverted through collectors to the San Diego Pont Loma sewage treatment plant, but with rapid expansion of San Diego itself, this plant was nearing its design capacity.

As a permanent solution, the USA Government, in cooperation with the Mexican Government and through the International Boundary and Water Commission, built a new treatment plant close to the Mexican border on the USA side near Tijuana. At a cost of $265 million, the new plant will treat overflows from Tijuana’s sewer systems.

Once the overflows are treated, the deal with Mexico is that the effluent is discharged out to sea through the ocean outfall and the stabilized solids transported back across the border to Mexico for final disposal.

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After contract award, Traylor/Obayashi signed an order with Mitsubishi of Kobe, Japan, and Boretec of Solon, Ohio, for design and manufacture of an EPB TBM and its trailing back-up. “We chose an EPBM over a slurry TBM for a couple of reasons,” said Mike Jatczak, Project Engineer for Traylor/Obayashi. “First, contract partners Traylor Bros had just finished, in joint venture, the St Clair Tunnel in Canada using a Lovat EPBM and so had recent experience with EPB technology. Also, EPB is less expensive to mobilise. A slurry TBM carries high up-front costs to set up the separation plant, which is then a relatively costly and specialised system to operate throughout the drive.”

But the EPBM supplied by Mitubishi is far from standard.

In meeting the detailed contract specifications, the TBM includes some quite distinctive features. The most obvious is the man-entry in-shield compressed air drilling chamber immediately behind the shield’s bulkhead. This is required because of the combination of high ground pressures and very abrasive material and the need to apply pressure within the plenum and establish ground freezing around the machine if necessary.

Phase 1 of the new treatment plant had an average treatment capacity of 25 million gal/day, peaking at 75 million gal/day.

While the cost of the treatment plant was funded primarily through the USA Environmental Protection Agency, with some contribution from the Mexican Government, the $135 million outfall was funded jointly with the City of San Diego. Through its $58.8 million cost contribution, the City purchased up to 40% of the outfall capacity to discharge treated effluent from its new water reclamation facility, to be built next to the new treatment plant.

Unfortunately, the treatment plant and its outfall ran to different project construction schedules. The first phase of the international treatment plant was under construction from mid-1994 and was commissioned in April 1997. The outfall, meanwhile, was programmed to be commissioned in mid-1998. For the interim 16 to 18 months, treated effluent will be pumped through existing trunk sewers to the Point Loma plant for further treatment and discharge via the plant’s 4.5 mile seabed pipeline outfall. Under the USA Government’s Clean Water Act of 1972, only effluent treated to secondary standards can lawfully be discharged through the outfall.

“Drilling could have been carried out in free air from behind the plenum bulkhead,” said Jatczak, “but we need to drill out through the bulkhead to install the ground freezing array. With no room for both drilling ports and airlocks on the bulkhead we had to move the airlocks back, which introduced a second bulkhead and the interim pressure chamber.”

Although this 5ft long chamber gives the 13ft diameter shield a long length of 36ft, and a high length to diameter ratio of 2:8, it provides the option of using compressed air during any drilling operations and will give face crews a larger working space and a second line of defence against the earth pressures during compressed air man entries. There is also the added benefit that tunneling can restart while the face crew is in decompression.

The chamber is serviced by two airlocks. One is the main man lock, which can hold three people, while the other is mainly a materials lock but is large enough to hold one person. The drill chamber and its airlocks are designed for a minimum 3 bar pressure and the compressors needed to operate the facilities are located on the surface, with a smaller capacity secondary system on the TBM back-up.

The 34 drill ports around the perimeter of the drilling chamber allow a freeze array of up to 15ft ahead of the face and up to 25ft in diameter, or twice the size of the 13ft shield diameter.

Pressure balance

The second most distinctive feature of the Mistubishi shield is its 180ft long screw conveyor. As well as dissipating a theoretical 14-15 bar of earth pressure via the plug of material created within the flights, the long screw also effectively replaces the transfer conveyor belt of more familiar EPB machines. Muck is carried all the way to the loading bay, where the discharge gate opens directly into muck skips.

plate. The cutterhead is also fitted with three wear detector pads. These simulate scrapper teeth in which an oil pressure probe is drilled to within a certain distance of the outer surface. Loss of pressure indicates the extent of wear on the sensor pad and, by association, on the tools of the cutterhead as a whole. The scrapper teeth and the disc cutters are all back loading and the muck ingress slots of the cutterhead are protected by hydraulically operated flood doors to seal off the face during man entry maintenance periods.

The TBM is driven by three electro-hydraulic drive motors for a total power installation of 115kW. Seven hydraulic motors then turn the 3.9m diameter cutterhead at a variable speed of 0-2.4 rev/min and operate the 18 thrust rams which will exert a total forward thrust of 2,000 tonne and generate a maximum torque of 150tm.

As is now standard practice for EPBM applications, the contract specifies the use of conditioning agents to ensure an effective pressure-reducing impermeable plug of muck within the screw conveyor and to lubricate the material to reduce abrasive wear and lower cutterhead torque. To meet the specification, Traylor/Obayashi will employ a surfactant polymer foam supplied by Boraid.

It will be used systematically throughout the drive and will be injected at between 4-7 bar pressures. According to Jatczak, consumption of foam during the drive is expected to be about 30% by volume of muck excavated.

Conditioned muck is to be hauled about five miles to a licensed disposal site.

The EPBM is designed to withstand 10 bar pressure. The tail seal is a three-row wire brush system and the tail seal mastic will be injected through delivery pipes on the outside of the shield. Annular grout is injected through the segments.

Choice of lining options

“Given the option of a one- or two-pass lining, we chose the one-pass system,” said Jatczak. “Again, we had had The screw comprises two parts. The first is the 30ft long recent experience of a one-pass system on the St Clair primary screw rising from the invert of the plenum and is a Tunnel.” Sehulster, the company that manufactured the ribbon type screw. The second is the 150ft long horizontal segments for St Clair, is working in JV with Precon of auger-type screw which runs over the top of the trailing California to produce the segments for this job at a factory gantries to the muck loading bay. The first screw is driven about 80 miles away near Los Angeles. by a 3.8tm electric drive motor at a rotation of 7.7 rev/min.

The second is also driven by a 3.8tm motor and rotates There are four segments and a key in each 4ft wide x at 7.1 rev/min. There are three gates in the system. One 230mm thick x 3.4m i.d. ring of precast lining. The segments at the plenum bulkhead, another at the junction between are reinforced with about 270kg/m3 of rebar and are fitted the primary and the horizontal screw sections, and the discharge gate at the back. Grizzly bars across the muck ports limit the ingress of material TunnelTalk references to cobbles of up to 12in maximum. Larger boulders must be broken up by the machine’s • Set up for Detroit’s second effluent outfall - April 2009 nine double-ringed disc cutters.

• Detroit outfall contract terminated - April 2009 •

Brightwater wastewater conveyance mobilization - September 2007

In anticipation of the high wear and the length of the drive, the specification for the machine was uncompromising. It demanded that spares for vital components of the machine be either on site or within days of delivery. These spares included spare screw conveyors complete with their barrels and a replacement main bearing, bull ring and cutterhead seal, all replaceable from within the tunnel.

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Brightwater action to limit costly delays - February 2010

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Excavation complete on Brightwater - August 2011

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Court rules against Brightwater contractor JV - December 2012

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Breaking new ground on LA outfall tunnel - June 2015

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Mobilizing for the Los Angeles wastewater drive - March 2021

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Vice President speaks of DC Water Clean Rivers project - April 2020

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Storebaelt - the final chapters - May 1995

The cutterhead and shield body is protected with extra hard-wearing surfaces and welded

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Storebaelt calls on Project Moses for support – April 1993

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Court find for the St Clair engineers - December 2008

Wear considerations

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with straight bolts across the radial and longitudinal joints. The joint seals are HDPE gaskets supplied by Heinke, which have been tested successfully to 14 bar pressure. The machine is fitted with a mechanical erector.

In operation, the one-pass tunnel lining is expected to behave as well as tunnels are known to in the event of earthquakes but in identified seismic zones, larger diameter bolts will be used on the longitudinal joints and the bolt holes will be grouted up. There are ten identified seismic zones, which total about 10% of the tunnel length.

On site, the tunneling system is geared for an optimum advance of one 4ft ring/ hr. Trains of three 8.5yd3 muck cars, two segment cars and a grout car pulled by 8 tonne Balco diesel locos will service the heading. The three muck cars will carry the muck from one 4ft shove and each skip will be lifted out of the shaft Nitrogen ground freezing was required to back up the primary brine freezing for discharge. There is a car passing system following a breech at 88.5ft into shaft excavation switch in the bottom of the shaft and a 300ft long California will be installed as the tunnel advances.

The 158ft deep riser shaft, the seabed section of the outfall and the diffuser legs were installed from floating platforms

Marine riser shaft operations

Installation of the riser shaft is being completed for Traylor/Obayashi by subcontracter Case Foundation.

Working from a fixed drilling platform, Case started by using the lower casing as a pile driver to hammer in a 54ft long x 11ft diameter x 2.5in thick steel casing.

The core was then excavated and a second 113ft x 13ft diameter casing was hammered down inside. Once the annulus between the two had been cleaned out and grouted up, Case used a foundation drilling reamer to excavate the core of the second casing to full 1,757ft depth. The foundation drilling reamer also created a cavity at the bottom of the casing which was tremmied full of concrete. It is into this block of concrete that the EPBM will end its drive and for the shield to be abandoned. The upper half of the 9ft diameter elbow into the riser will be installed from the marine platform, while the lower half will be installed through the tunnel.

The riser was started in October 1996 and will finish in June 1997. Separate contractor, Fletcher General is laying the final 4,670ft of the outfall and the two diffuser legs in trenches on the seabed. The pipe and the tapered diffuser legs were prefabricated and floated out on barges for installation.

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The tunneling schedule is based on three 8hr shifts/ day working 24hr/day, six days/week with maintenance on Sundays. The optimum advance rate of 4ft/hr equals 24 shoves or about 100ft/day. Excavation of the 3.5 mile long drive is programmed over 12-13 months within the 30 month tunneling contract. Predicting the eventual average advance for this demanding tunnel however is practically impossible. The difficulty of working through this alluvial material has already been experienced during excavation of the access drop shaft. In the porous alluvial material of Reach 1, Traylor/Obayashi chose ground freezing as the method of sinking the 36ft i.d. shaft. Subcontractor Layne North West was engaged to install a brine freezing system to a depth of 300ft, well below the base of the 200ft deep shaft. The freeze wall was up to 10-14ft thick.

Everything progressed according to plan until a breech in the freeze wall at the 90ft level caused an inundation.

The shaft filled with 50ft of water and had to be back-filled with sand to within 20ft of the surface.

After much discussion it was accepted that the breech was caused by an undetected and isolated high velocity flow of groundwater. It was eventually agreed that it could be frozen successfully using liquid nitrogen. Although very expensive, the nitrogen option was more cost effective than conversion to a totally different method of resinking the shaft, considering the time factor. It was agreed to connect four to six holes of the brine ring to liquid nitrogen injection to close the breech zone. Now protected by brine and nitrogen systems, re-excavation commenced.

Successful freeze sinking

“This proved successful,” said Chief Resident Engineer Colzani. “Excavation reached the bottom without any further trouble but we had lost four months. Once excavated, it took another four weeks to finish the shaft with its 2ft reinforced in-situ concrete lining.” Zones of

gravels, cobbles and boulders uncovered in the shaft also confirmed geological predictions for the tunnel line.

In the meantime, the machine had arrived from Kobe, and the back-up trailers from the Boretec factory in Ohio.

During a site visit in early 1997, the shaft was complete, the freezing systems had been recently decommissioned and the TBM was in the bottom of the shaft attached by umbilicals to the operating systems on the backup trailers assembled on the surface and waiting to follow the shield down the shaft.

Progress in these early weeks was slow and a case if trial and error. Instead of foam, Traylor/Obayashi was using bentonite as a conditioning agent, which dissipated more rapidly. One of the major early concerns was that penetration of the cutterhead was proving problematic. Methods of resolving the penetration problem by adjusting the tools on the cutterhead, for example, would have to be undertaken from within the tunnel and under compressed air.

The TBM was still within the influence of the dewatering system installed to assist launch of the machine but

ground pressure of up to 4 bar had already been recorded.

The complexity of the ground, according to Jatczak, is such that pressures can vary markedly from moment to moment. From the start, the South Bay tunnel was proving to be as tough as had been predicted.

After progressing through the learning curve towards more consistent progress rates, the 13ft (4m) diameter Mitsubishi EPBM was 750ft (228m) into the 3.5mile (5.6km) long drive but was yet to pass out under the sea.

Once a rail track passing bay in the bottom of the shaft, and a man-lift and guide rails for lifting the muck skips in and out of the shaft had been installed, progress rates were expected to rise quickly towards 50ft (15m)/day.

According to Jatczak for Traylor/Obayashi, the machine is cutting a 4ft (1.2m) stroke in about 20 min and taking about 40 min to erect the four segments and key in each ring of over-pass bolted and gasketed precast concrete segmental lining. Best advance rates are achieved in the silts. In more gravelly material, torque increases and advance rates slow up.

San Diego interceptor powering forward SITE VISIT REPORT: JUNE 1997

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aturated sands of fine to medium to very dense in nature, with lenses of silts and clay and layers of shell fragments are presenting no problems at all for the Lovat EPBM excavating a sewer through the coastal geology of San Diego, Southern California. The 4.5m (181in) diameter Lovat machine started boring in April 1997 and to the site visit in early May 1997, it had completed 390m (1,280ft) or about 30% of its 1,350m (4400ft) long drive, erecting a primary precast concrete bolted and gasketed segmental lining as it goes. The machine is maintaining an average production of 12-13 x 4ft (1.2m) wide rings or 14.5-15.8m in every 10hr production shift and is cutting through the ground with very little difficulty.

The tunnel is the last section of a new Interceptor sewer for the City of San Diego Metropolitan Wastewater Department conveying sewage from the north of the city into local pumping station for transfer to the city’s main treatment plant. En-route, the tunnel passes beneath USA Navy property, under the runways at the west end of the international airport, and follows a major city street, before meeting the end of the already-completed Phase 1 tunnel of the North Metro Interceptor project.

The new Phase II tunnel lies up to 7.6m (25ft) beneath the surface, well below the natural ground water table and close to the marina and the Pacific Ocean bay. The water table is influenced marginally by ocean tides and presents hydrostatic pressures of up to 1 bar at tunnel invert. In these geological conditions, Haley & Aldrich/Montgomery Watson, the City’s tunnel design JV, instructed the use of an EPB TBM to safely excavate the saturated ground, protect the natural ground water regime and prevent ground losses.

Haley & Aldrich/Montgomery Watson also designed a twopass tunnel lining with a precast concrete pipe backfilled

into the primary precast concrete bolted and gasketed segmental lining. The composite lining is needed to resist attack by aggressive elements in the wastewater and ensure a robust structure capable of withstanding with confidence the ground movements and earthquakes that disturb southern California from time to time.

TBM selection

Contractor for the job is a JV between local companies Elmore Pipe Jacking and LH Woods & Sons which emerged as the best of four competing groups when bids were opened in May 1996. The bid price of $18.383 million was accepted and notice to proceed was granted in September 1996.

In selecting its machine, the JV approached five machine manufacturers including Mitsubishi, Boretec, Robbins/ Kawasaki and Dosco of the UK. “Eventually we opted for the Lovat concept,’’ said Bill Elmore, Owner and Managing Director of Elmore Pipe Jacking and Project Director for the JV. “This the first EPB and first Lovat machine used by either of the JV partners and in making our decision we were concerned about the ready availability of consumables and spares and a commitment to aftersales service and technical advice. Lovat has a long history of supplying tunneling machines for different projects around the world (our TBM is, I believe, the 175th machine supplied by Lovat) and we felt satisfied that the company would supply a machine that would meet the contract specifications and deal successfully with the predicted ground conditions.” The order for the machine and its back-up was placed in August 1996. It was ready in January 1997, shipped in late February, and arrived on site in March.

In addition to the standard TBM requirements, the Lovat ME181SE machine is fitted with gas monitoring equipment and an automatic shut-down system. The tunnel passes under an old landfill site which the USA Navy operates as a training facility. This contains possible contaminants including gasoline and diesel as well as highly toxic vinyl 51

Cutterhead and section of the 4.8m Lovat EPBM with the operator controling the TBM and segment erector to manage excavation of the saturated alluvial sands

chloride. The stockpile of muck must be tested every 100yd3 for gasoline and diesel and every 1,000yd3 for chlorides before being transported off-site for either normal disposal or special handling.

Coping with potentially contaminated ground was one reason for rejecting a slurry-based TBM system.

According to Elmore/Woods Safety Officer, contaminated slurry would also require special handling and a slurry operation would complicate isolation and disposal of noncontaminated muck piles. In addition, it was suggested that a substantial and multi-component separation plant would be needed to cope with the volume and quality of the material excavated. “We own and operate a remotecontrolled slurry microtunneling machine and know that a separation plant of substantial size would be needed to cope with the 650yd3 (about 500m3) of material we are extracting on average/day,” said Elmore. “Mucking out using skips and locos can create a bit of a mess if the material turns sloppy, but this is the best method of dealing with these conditions.”

TBM specifications

The Lovat machine is fitted with a 32ft long x 24in diameter (9.5m x 600mm) auger screw conveyor which will be in use for the entire 1.3km long drive. The TBM is powered by three x 250hp electric water-cooled motors 52

driving the cutterhead at variable reversible speeds. The 16 x 125 tonne push cylinders provide a total thrust of 2,000 tonne and 5,000 psi. The screw conveyor runs at a variable, reversible speed of between 0 and 30 rev/min and is fitted with two EPB cells.

The main bearing and its vital sealing arrangement is of a new Lovat design which has been developed for technically very demanding projects. The new profile lip seal is of a more dense, more hard-wearing material and it is housed within a tighter, more compact seal housing close to the bearing itself. The labyrinth of the main bearing seal is positively and continuously fed with a thick lubricating mastic and an automatic shut down is triggered should grease feed stop for any reason. Water or surfactant foam can be injected through nozzles on the cutterhead as well as directly into the excavation chamber and into the casing of the screw conveyor if needed to condition the material and facilitate optimum EPB operation. Hydraulic oil, grease, bearing seal mastic, and fibrous wire brush tail seal grease are all supplied to the job by Condat of France.

Site set-up

While the machine was in fabrication, Elmore/Woods prepared the working site to include set up of a casting yard for production of the precast concrete segments

Working shaft of the new sewer with alfresco segment casting on site

and a long, sheet-pile supported working access shaft.

The long working shaft was Elmore’s alternative to the original circular access shaft. “We have in any case to complete a length of cut-and-cover to link the tunnel to the existing 96in sewer line and decided that excavating part of this ahead of time would be an advantage to the tunnel operation. The long shaft allowed the TBM and its back-up to be fully assembled before being launched and now provides much easier access to the service trains.”

The segment casting yard is set up in the open air under the reliable, clear blue skies of Southern California.

Designed by Parsons Engineering Sciences of La Jolla, California, each 1.2m (4ft) wide x 229mm (9in) thick ring in the bolted segmental lining comprises five segments and a key. The casting yard has 50 segment moulds and 10 key moulds supplied by EFC, Economy Forms Corporation of Des Moines, Iowa, to produce segments for 10 rings/day. After striking the segments early each morning, the moulds are prepared and first deliveries of ready mixed concrete (bought in at more economic rates than setting up an on-site batching plant) start at 8.30am. Steam curing under tarpaulins at 120-125˚F allows the lightly reinforced segments to be struck with compressive strengths of 2,500psi (17N/mm2). The segments then acquire a strength of 3,000psi after 24hr and the design strength of 6,000psi (42N/mm2) after 28 days. According to the casting yard manager, only six segments in the 752 rings (4,512 segments and keys) cast so far have been rejected and three of these were damaged in handling. The segmental lining is not trapezoidal and wooden packers are used to negotiate the alignment curves. As the first of a two-pass lining system, the segments are fitted with only a light sealing gasket which is affixed to the smooth rather than grooved edges of the segments. “We were concerned that these seals would suffer frequent displacement or damage during the ring build,” said Craig Kolell, representative on site for the owner’s construction supervision and project management JV Sverdrup/ICF Kaiser. “The rings, however, are building very well and the tunnel so far is of a good quality with few visible leaks.”

When complete, the tunnel will be finished with 3.6m (12ft) long x 2.8m (114in.) i.d. x 27 tonne precast concrete pipes that are being fabricated by Ameron Pipes of Riverside, California. Elmore/Woods has a pipe carrier which will start installing pipe at the far end of the tunnel and work back towards the access shaft, retrieving construction rail and service lines as work progresses. Once installed,

subcontractor Pacific International Grout Co will backfill the 175mm (7in) radial annulus with a light-weight cellular concrete. Following pipe laying, the finished contract is scheduled to be signed over to the owner in April 1998.

Meanwhile, excavation continues at better-thanexpected rates. “Our contract schedule is based on an average rate of 10 x 4ft rings or 12m/10hr shift,” said Red O’Conner, Project Superintendent. “We are actually achieving an average of 12 to 13 rings or 14.5-15.8m/shift and have recorded a best to date of 18 rings or 22m (72ft) in a shift. It is taking about 10 min to bore and 15 min to build each ring.”

The high advance rates were consuming segments at a faster rate than planned and an extra casting operation on a Saturday was introduced. If the tunnel catches up on segment production again, the situation will be shortlived, with the segment stockpile running out almost concurrent with tunnel breakthrough. Tunnel production progresses on two x 10hr shifts/day, five days/week with a half-day maintenance shift on Saturdays. Given current average rates, a breakthrough into the reception shaft is programmed for late June 1997.

When asked directly, Elmore said that the joint venture was very pleased with the Lovat machine and system. “It is running as expected; line and grade is accurate; normal regular maintenance is sufficient; and consistent progress is maintaining and slightly bettering the program average of 10 rings/shift.”

Over the first 250 rings or so, EPB performance under a working pressure of about 1 bar was said to be model with the material extruding from the screw conveyor in ideal condition and without the need of any conditioning agents.

The tunnel had since moved into bay deposits which include a higher content of silt and clay. “To avoid heave we must reduce the working pressure on the thrust rams from 2,500-3,000psi to about 1,500-2,200psi. However, although reduced, this pressure squeezes more water out of the material, causing the drier more-silty material to pack in the screw,” said George Bonhomme and Skip Hurlimann, Shift Superintendents. “We have been using water in the plenum and in the screw to prevent blockages, but while this does lubricate the material it does not mix well, causing sloppy wet muck at the top of the muck skips that spills over on the journey out of the tunnel. This will improve when we move back into the sands of the Terrace Deposits.” n 53

CASE STUDY: In managing pollution of its waterways, the urban areas of the city of Atlanta, Georgia, in particular had to adopt an intense program of tunneling to meet consent decree undertakings with the USA Federal Environmental Protection Agency. Spearheading the effort, the Mayor of Atlanta herself took personal charge of communicating with the residents and taxpayers to meet the deadlines.

While the City of Atlanta funded early progress on its projects, it pursued also a Federal funding contribution, as the projects would benefit Alabama and Florida as the Chattahoochee flows southward to the Gulf of Mexico and is the source of many potable water systems along the way. The program in the 1990s and 2000s included the Chattahoochee project in Cobb Country, and the Nancy Creek and West Area projects for the City of Atlanta, with projects completed earlier and more planned for the future as the city continued to expand. Deep hard rock TBM excavations in massive metamorphic bedrock allowed much of the sewer system to remain unlined except in areas of weaker or faulted zones

Atlanta takes control Chattahoochee sets up with two rock TBMs SITE VISIT REPORT: NOVEMBER 1999

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ix to eight joint venture bids from some 18 major contractors requesting prequalification documents were expected in mid-October 1999 for the Chattahoochee sewer tunnel in Cobb County, Georgia at the start of a significant upgrade of sewer management for the city of Atlanta. The new 9.5 mile (15.2km) long x 18ft (5.5m) diameter hard rock tunnel is designed to provide increased sewerage collection and stormwater management in the rapidly growing Cobb County district.

Designed by Jordan, Jones & Goulding (JJ&G) for the Cobb County Water System, the bored tunnel was chosen over less expensive alternatives. “The tunnel has a higher capital cost than shallower open cut options,” said Refik Elibay, Manager of JJ&G’s Tunnels Department, “but it is the shortest route; it minimizes surface and environmental impacts and reduces permitting requirements, all major factors in this urban area. In addition, its storage or equalizing capacity limits the size and cost of the necessary treatment plant upgrade.” In July 1998, the Cobb County Board of Commissioners approved the tunnel proposal and JJ&G was commissioned to proceed with detailed design.

More than 15,000ft (4,500m) of core taken as part of the $1.1 million geotechnical investigation confirms that the tunnel passes through a range of metamorphic rocks including gneiss, schist, quartzite and granites. “These rocks are very hard at between 140-280MPa and will be very abrasive,” said Wojciech Klecan, Senior Geotechnical Engineer with JJ&G. “In addition, the rock strata are 54

intensely deformed, sheared, and altered by activity along the Breyard Fault which is a major 3 mile wide zone of deformation extending from Alabama to North Carolina.”

The majority of the rock mass has a rock quality designation (RQD) of 70-100% and is expected to be practically impermeable, except at the major geological features where localized inflow of 200-500 gal/min is anticipated. A zone of less competent rock is also identified, where soil-like seams are to be expected. To optimize favorable rock conditions, the tunnel horizon is deep at up to 230ft (70m) below ground surface at the shafts, and the maximum overburden is 350ft (106m).

uphill drives and will allow work in the permanent shafts, particularly the large pumping station shaft, to progress concurrent with tunnel excavation.”

Water ingress is not expected to be excessive, but the documents require a pumping capacity to handle a minimum 2,000 gal/min/one event/tunnel drive. A short, 1,500ft (456m) section of drill+blast will complete the tunnel connection to the permanent pumping shaft. The two TBM working shafts are 190ft and 230ft (58m and 70m) deep and 32ft (9.7m) in diameter. The pump station shaft is 170ft deep x 110ft ((52m x 33m) in diameter.

of its CSOs The civil construction program is based on the tunnel being in operation by October 2003. To meet the deadline, JJ&G has written documents for a 44-month civil contract using two hard rock TBMs of 18ft (5.5m) diameter.

“This will be a gravity-fed system with a 0.1% gradient down to the R.L. Sutton water reclamation facility near the Chattahoochee River,” explained Michael Robison, JJ&G’s Senior Tunnel Engineer. “There will be four permanent facility shafts, including the large 110ft (33m) diameter shaft at the downstream end designed to house all the necessary pumping equipment. The pumping shaft will save the cost and surface space needed for a surface pumping house.”

“The two TBMs will advance from two temporary construction access shafts - one near the downstream end and the other at about mid-point,” continued Robison.

“This will allow both TBMs to work in the same direction on

The project’s $270 million budgeted cost, of which an estimated $130 million is tunnel construction, is fully funded

by Cobb County Water System via local sources and requires no government bond issues. With funding secured, the invitation to prequalify for the single tunnel contract was advertised in August 1999 and bids from a select list of five to eight bidders are expected in January 2000. An earlier bid opening date of October 1999 was delayed by a section alignment change and the need for further geological investigation. Award of contract is expected within two months of the bid opening. “This is a traditional designbid-build contract,” said Elibay “and the client, as a public agency, will accept the lowest conforming bid.”

Having spent one year in design - a notably short period for a project of this size - JJ&G will continue its project association through the construction phase with three full time field engineers to monitor design requirements, map the geology, and review submittals from the contractor.

During design, JJ&G drew on the work it concluded in the early 1990s for the 8 mile long x 25.5ft (12.8km x 7.7m) diameter R.M. Clayton to Utoy stormwater sewer for the City of Atlanta, construction of which was canceled for social and political reasons.

“It is anticipated that as much as half of the Chattahoochee tunnel length can remain unlined,” said Elibay, “with an in-situ concrete lining to a 16ft (4.9m) i.d. being installed where necessary for long term support and where sources of high water ingress need to be sealed. Some pregrouting of the tunnel is also required and some areas of shotcrete may be needed to seal the rock. Mapping of the tunnel is therefore essential for immediate support and final lining requirements.”

New or used machines are permitted on the project, with the manufacturer certifying any used TBMs. The specified machine requirements, however, are strict. To cope

Geological section of the Chattahoochee Tunnel, which will pass through hard and abrasive metamorphic rock and cross various fault zones allowing about 50% of the of the alignment to remain unlined, with concrete lining only as necessary

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Two Robbins TBMs for the Chattahoochee contract made powerful headway through the massive schist and gneiss bedrock

with the very hard rock conditions, the TBMs must be capable of a minimum 30 ton (60kps)/cutter loading. Jerry Dollinger, an ex-Robbins employee, is undertaking the boreability tests and this high cutter loading specification would eliminate very old machines. In addition, the TBMs must be fitted with twin drills behind the cutterhead to install rock dowels, and another for probing ahead and for drilling pregrouting arrays. An erector arm is also needed for installation of steel ribs in crushed and faulted zones.

“This will be a challenging contract,” said Elibay, “and the client has adopted several mechanisms by which to avoid or resolve any possible disputes. There will be a system of risk sharing with the contractor, based on a three-part geological baseline report (GBR) comprising all the site investigation data, an interpretive report, and the set of baseline assumptions and expectations. There will also be a disputes review board (DRB) and the contract documents will be held in escrow.”

It is also expected that the successful contractor will use continuous conveyors for muck haulage, with vertical conveyors in the deep access shafts. The first civil use of a vertical conveyor was on the Intrenchment Creek combined sewer overflow tunnel project in Atlanta in 1984. The technique has been developed since and used extensively on USA projects.

Robbins TBMs tackle Chattahoochee drives

Diaphragm walls, which will also provide the permanent support system, have been specified for shaft excavation through the overburden. Groundwater contaminated by an old paint factory along the alignment also demands particular attention. Pre-excavation grouting is specified to precede drill+blast excavation of the two shafts closest to the contaminated groundwater plume, as well as in the TBM-driven section of the tunnel between them. To further prevent subsequent movement of the contaminated plume, both shafts and the connecting segment of tunnel will be fully concrete lined on completion.

Project Manager for the Cobb County Water System is Judy Bowers and the client’s Project Director is Steve McCullers. To accord with internal policy, the project will be administered and supervised by an independent construction management team. This contract was recently awarded to Parsons Engineering-Science with its subconsultants Jacobs Associates of San Francisco.

The group won the well contested contract out of a list of seven written proposals received by Cobb County.

The other teams included Parsons Brinckerhoff with Construction Dynamics Group and Moreland Altobelli; ICF Kaiser with Stone & Webster; Bechtel with Mayes Sudderth & Etheredge; O’Brien Kritzberg with URS Dames & Moore; CRSS Sverdrup with Black & Veatch; and Heery with Hatch Mott MacDonald. The ICF Kaiser group and the Parson-Engineering group were the two shortlisted contenders invited to make team presentations in July.

The $8.5 million Construction Management contract covers contract administration, quality assurance monitoring, cost and budget control and management, and supervision of all project safety requirements.

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SITE VISIT REPORT: JULY 2002

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n mid-2000 the contract was awarded to the joint venture Gilbert Southern/SA Healy when it presented the lowest bid of $113.6 million. To meet with the specified requirement, the JV selected two hard-rock Robbins TBMs for project.

The two TBMs - one new, and one refurbished and complete with their trailing backups - are due on site from the Robbins workshop in Solon, Ohio, in May and August 2001. Both the horizontal and vertical conveyor systems selected to muck out behind the TBMs are supplied to the project by Robbins Boretec Conveyor Systems based in Oak Hill, West Virginia.

The two Robbins TBMs are almost identical. Both are open main beam gripper TBMs with identical back-ups, the same cutterheads, and fitted with up-front drill rigs for roof bolting, probe drilling and grouting, and with grout mixing stations on the back-ups. The cutterheads are dressed with 19in Robbins cutters and a water spraying and foam additive system controls dust created both at the TBM and on the continuous conveyor.

In fulfilling its order to the JV, Robbins President Lok Home explained that the company has established a partnership with its contractor to produce better efficiencies. “The Gilbert/Healy partnership started months ago, in the design stages for the two TBMs and the two seven-stage conveyors systems. It will continue on site where the tunnel is to be excavated over an 18-month schedule.”

Vice President Joe Roby said that, “working closely with the contractor, utilizing the partnering concept, will produce the best equipment for the project and maximize performance in the field. The knowledge gained will enhance future development.”

By September 2002, the two TBMs were more than 75% into their drives and breakthrough for each was expected in October and December. “We are averaging about 100ft/ day for each 5.5m diameter TBM, working three 8hr shifts/ day, 5 production days/week,” explained Rick Kimball, Project Manager for the Gilbert Southern/SA Healy JV during a site visit in late July 2002. “Since being launched in July and November 2001, one machine is now more than 17,000ft into the 22,000ft South Drive, and the other is more than 16,000ft into the 25,500ft North Drive.”

The two machines are boring through mica schist and granitic gneiss of up to 27,000psi. “Rock conditions for the most part have been highly favorable for TBM excavation,” said Jack Raymer, Geologist and Geotechnical Engineer with project design engineers JJ&G. “The South Drive did run into a predicted length of wet, broken and blocky schist with seams of soil like infills that required installation of Type C support, comprising 6in steel ribs on 4ft centers, that did reduce TBM rates, but the drive has since passed into harder gneiss and rates have improved.” Water ingress peaked at about 700 gal/min.

In the North Drive the used TBM started in softer schist and has moved into harder granitic gneiss which is expected to prevail to the end of the drive. Support in the North Drive has comprised mainly spot bolting with mesh and channel strips as required or the bolting patterns of support Types A and B, comprising four bolts on a 6ft pattern for A and six bolts on a 4ft pattern for B. The Norwegian-developed CT bolts supplied in the USA by American Commercial are being used.

The extension loop take-up units of the Robbins continuous horizontal and vertical conveyor systems behind the TBMs are located on the surface and there are two booster drive units on each of the 22,000ft+ (6.7km) headings.

Systematic probing is required in designated zones and a program of extra probing and grouting is required to grout up any major water bearing fissures. After grouting off the zone of blocky wet ground in the South Drive, water make in both headings has remained consistent at about 500 gal/min and within predictions stated in the GBR. Once excavated, much of the 18ft o.d. sewer will remain unlined with in-situ concrete applied to about 26,000ft of the total 48,000ft and a short 456m drill+blast heading will link the TBM tunnel to the larger 33m diameter x 52m deep pumping station shaft at the downstream end from where flow will be lifted into the treatment works.

When on site in late July 2002, the North Drive TBM was down for repair of a broken motor drive shaft and

Casting an in-situ lining where required to finish the Chattahoochee project

a damaged bull gear. Preliminary metalurgical reports indicate that microscopic subsurface flaws in the ring gear forging may have caused the failure. “We have worked with Robbins to get the machine up and running again as quickly as possible,” said Kimball. Under the partnering type agreement, a full time Robbins technician is assigned to the project to monitor performance and participate in maintenance of the TBMs and the conveyors.

Reports from site indicated that the repair was completed with the loss of only few production days and that all had been progressing well and up to speed since then. The Robbins 19in cutters, according to Kimball, also maintained good cutter life in the abrasive, high quartz content rock.

By May 2003 all excavation on the 15.2km long tunnel was complete and concrete lining as required was underway.

The first of two Robbins TBMs finished its 7.7km long North Drive in December 2002 while the second machine broke through in March 2003 after completing its 6.7km long South Drive.

About 8km of the total 15.2km long tunnel requires concrete lining. Using a 210ft (64m) long form from Everest of Canada, the JV is achieving an average 100ft (30m)/ day and working towards increasing this to a 180ft (55m)/ day average. Meanwhile work is continuing to complete the shaft pumping station and excavation of the five drop shafts required on the alignment. “We are close to completing the civil works on the pumping station,” said JV Project Manager Kimball, “and we expect to complete the last two of the raise bores by the end of July.” At a budgeted cost of $270 million, work was on target to meet the contract’s October 2003 in-operation deadline.

Nancy Creek sewer forced into tunnel SITE VISIT REPORT: MAY 2001

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ancy Creek was part of an estimated $3 billion capital investment program by the City of Atlanta to respond to consent decree agreements with the Federal Environmental Protection Agency (EPA) to prevent frequent combined sewer overflows.

tanks. When the plans were released to the public, the residents of the affluent Nancy Creek neighborhoods, that include the Governor’s Mansion and the Buckhead financial district, objected forcibly and insisted that the new facilities be installed in tunnel.

Originally, the City of Atlanta Department of Public Works planned to meet the mandated requirements by installing a series of open trench forced mains and retention storage

Once the decision to adopt the tunnel alternative was agreed, Jordan Jones & Goulding (JJ&G) was engaged as tunnel design consultants. “In discussions with the 57

TBM excavation through massive hard bedrock was up to 300m below the surface

High profile public involvement

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uring one of several visits to Atlanta, Mike Robison, JJ&G Resident Construction Manager for the Nancy Creek project said: “This project has had a very high public profile. We had to pass directly beneath or close to 200 private homes with 108ft to 330ft (33m-100m) of cover. Residents of this exclusive neighborhood of Atlanta were very engaged and concerned about our activities. As engineers, we had to not only promote the idea and the need of this new tunnel, but also explain the inconvenience and disruption that it might cause during construction. Interestingly, it was the owners of the most expensive properties that in many cases were most co-operative and supportive. It was a very interesting project all round.”

According to Robison, “the interest for the project is no less. We don’t impact as many private homes but the tunnels are as long and much larger in diameter.

A dedicated stormwater tunnel facility is needed for the west area of the City of Atlanta to convey CSO flows from three existing mini-treatment plants and prevent the 60 or more times that the system CSOs activate to discharge untreated combined sewer flow into the tributaries of the Chattahoochee.”

At a town hall meeting to explain the projects, some local residents were looking to the project engineers and owners to guarantee the value of their properties at current market value, in fear of the tunnel and its construction causing a fall in the value. This the city could not underwrite and the chances of any harm coming to any property on the tunnel alignment at up to 100m below the surface in hard rock was very low to zero. Perhaps there would be some noise or vibration as the TBMs passed through, and once a question was asked to visualize exactly how deep is 300ft, 100m, compared to the height of the hall, the heat was taken out of the discussion.

The West Area CSO is part of a $3.2 billion program by the City to separate the last of its existing combined sewerage networks. The program includes upgrading treatment facilities and rehabilitation of ageing systems. In addition, there is the potential for other large tunnel projects.

The demanding capital investment by the City of Atlanta in sewerage and drainage is a result of having ignored the needs by past State and City Governments. In an inspiring keynote address to the NAT North American Tunneling conference in Atlanta in June 2004, Atlanta Mayor Shirley Franklin described how, after dubbing herself the Sewer Mayor, she faced the situation, established an implementation and management strategy, and used all manner of means to secure the funding to complete a $3.2 billion capital works investment over ten years (see page 64). Current works by the Obayashi and JJ&G teams is a major part of reaching the City’s goals.

A TV documentary on the History Channel in April 2006 focused on the West Area CSO project in Atlanta. Entitled Super Tools: Tunnels, the hour-long program followed the application of the two Herrenknecht rock TBMs. “The TV professionals were with us for about five days and while accommodating lights, cameras, and action, the show was something new for all of us tunnelers and it was a positive experience,” said Robison. “The greatest concern from their perspective was catching all the action of the construction process. For us, our work was another day in the office.”

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client since being appointed in December 2000, the extent of the project has expanded significantly,” said Refik Elibay, Manager of JJ&G’s Tunnels Department. “From an original project of 6.5km of 3.6m o.d. (22,000ft x 12ft) tunnel, the length was first increased to 9.5km (31,000ft). It is now likely to be increased again to 12.8km (42,000ft) of 6m (19.4ft) diameter, pending completion the hydraulic analyses.” This is nearing the same size as the Chattahoochee project for Cobb County.

As a court-ordered project, Nancy Creek must be in operation by the end of February 2003. Failure to meet the consent decree dates will trigger a schedule of punitive fines against the City of Atlanta.

“Meeting the completion date for a project of this scope is a serious challenge, for both the design and construction teams,” admits Elibay. “To expedite the schedule, the City has adopted a design-build procurement for Nancy Creek. We will complete design to about 30% and will have documents ready for a design-build request for proposals by late June.

Qualifications of the design-build teams will be evaluated at the same time as the price proposals.”

Funding for the project’s estimated $80-100 million budget is being secured from various sources. The City has allocated sufficient funds from its annual capital investment budget for engineering and early construction activities and additional funds will be available from the local governments of the adjoining DeKalb and Fulton Counties. Sewage from these counties is piped for treatment at the City of Atlanta’s R.M. Clayton treatment facility. The City is also pursuing possible funding from the EPA. The balance will be financed through the bond market.

Given the scope of the project and its limited construction period, the tunnel is designed as a TBM operation.

“The geology is similar to that of the Chattahoochee project, consisting largely of hard metamorphic rocks — gneiss, schist, quartzite and granites,” explained Elibay. “TBM excavation is the baseline design with a concrete lining to the likely finished diameter of 5m (17ft).”

In March 2002, the Obayashi/CBJ Contracting JV emerged as the apparent lowest of five bidders for

Jumbo arrives to drill+blast the TBM starter tunnel for Nancy Creek; Drill+blast excavation of a TBM starter tunnel

the project. The $138 million bid narrowly edged out the second bid of $139.9 million submitted by the JV led by Frontier Kemper with Bradshaw and Gunther Nash. The other bidders were Affholder/Archer Western/Capital Contracting JV at $144 million; Modern Continental South/ Polote JV at $156 million; and JF Shea/Traylor Bros/ MassAna JV $157 million.

To complete the court mandated project to be in service

by August 2005, the contract is based on working 24hr/ day, 7 day/week using two TBMs through the hard metamorphic rocks with the potential of introducing a third TBM if necessary. As well as fines that start with $1 million on the first day late, the City is also under pressure to get the project finished as “there is a citywide moratorium on connecting new sewer collectors to the existing overloaded system until this interceptor is in operation, and there is tremendous pressure from real estate developers to get the project started,” explained Elibay of JJ&G. In mobilizing for its contract, the Obayashi/CJB JV concluded an agreement with Gilbert Southern/SA Healy JV to use the two Robbins TBMs that it used to complete the Chattahoochee drives in Cobb County.

By end 2002, the Obayashi/CJB JV had completed sinking the TBM access shafts and was preparing to

launch the two Robbins TBMs during the Summer. “The TBM to work north from the R.M. Clayton shaft has arrived on site and is being assembled at the shaft bottom ready to start boring by mid-June,” said Mike Robinson, Resident Construction Manager on the project for JJ&G. “At the Roswell shaft about 30ft of the drill+blast starter tunnel is complete and the TBM components are due to start arriving in July.”

Nancy Creek into final phases SITE VISIT REPORT: JUNE 2005 By mid 2005, TBM excavation was approaching its end and concrete lining was also in the final stage. As a sanitary sewer, the full 8.3 miles of tunnel requires a full round in-situ concrete lining to 16ft (4.9m) i.d.. During a site visit in March 2005, Jamie Bonner Obayashi Project Manager said: “The TBM mining phase was uneventful.

The geology was great. The rock was actually not as hard as anticipated and there was hardly any slabbing. We beat our program estimates and installed only six rib sets in 8 miles. The two refurbished Robbins TBMs worked well. There were no major mechanical downtimes and utilization was good. We used plc computer controlled horizontal and vertical continuous conveyors for muck haulage. Once the first TBM from the Roswell working shaft completed its 17,000ft drive in late May 2004, we

Breakthrough of the first of two Robbins TBMs on the Nancy Creek contract; Progress of the Everest concrete lining form

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had to wait until we were pumped out on the Roswell side. Once up and running again, we have progressed concrete works in both tunnel drives at one pour/day, 5 days/week with 240ft of form in the Roswell drive and 210ft of form the Clayton drive. We are using Moran cars for concrete delivery in the Roswell drive and Maxon cars on the Clayton tunnel. The concrete is retarded for a 3-3.5hr life and attains about 3,000psi strike strength at 10hr.”

Concrete lining of one of the connecting adits

started concrete lining using a 240ft full circle telescopic form supplied by Everest of Canada, and Putzmeister concrete pumps.

“We ran into trouble when Hurricane Ivan swept through on September 16, 2004, flooding the full 3.5 miles of the Roswell drive all the way to the top of the 180ft (55m) deep working shaft. The TBM was already out, but all of the concrete equipment was flooded. It took us 10 days to pump out the water. We then needed time to clean the tunnel, retrieve equipment, and dry out all the electrics and works equipment before we could get started again.

Both tunnels had been evacuated well before, but, due to safety concerns and power supply problems, we had to stop advance of the Clayton shaft tunnel TBM because it was close to breakthrough into the Roswell shaft and

“The lining in the Nancy Creek sanitary sewer is unreinforced mass concrete,” said Ade Abon, the City of Atlanta Project Manager for the Nancy Creek contract.

“The lining is required also because we have to limit ground water inflows to ensure efficient operation of the treatment works. The total ground water inflow at completion of tunnel excavation was 1,400gal/min.

This needs to be reduced to a challenging 220gal/min specification. To achieve this, an extensive amount of contact and secondary grouting will be undertaken.

The challenge is having sufficient time for the needed grouting. As of May 2005, grouting in a 3,000ft long test section had reduced ground water inflow from 139 gal/ min to 7 gal/min.”

“Probe drilling was undertaken for about 25% of the tunnel through zones of possible high water inflows, but none hit the 20gal/min/100ft of probe inflow rate that would have triggered a program of pre-excavation grouting,” said Robison. “Pre-excavation grouting was undertaken in the 600ft drill+blast connection adit under the Nancy Creek, where groundwater inflows through the 150ft of fractured rock cover were higher than the trigger level.”

Reports from the job site in mid-May 2005 confirmed that the project, was on target to meet its 31 December 2005 court-ordered operating deadline.

Nancy Creek meets deadline

In early 2006, Mayor of Atlanta Shirley Franklin met with (from left) Ade Abon, Assistant Watershed Construction Manager; Mike Robison, JJ&G Resident Construction Manager; and Wojciech Klecan, JJ&G Lead Designer on a visit to the works for inauguration of the Nancy Creek system and then joined Refik Elibay, Project Manager of project engineers JJ&G (right) and Rob Hunter, Commissioner of the Atlanta City Council, Department of Watershed Management (left) to celebrate with others the completion of the 8.3-mile project. Started in July 2002 by contractor Obayashi Corp/CJB JV, the project met its consent decree deadline of 31 December 2005 and was completed under budget. Echoing Mayor Franklin’s comments, Elibay said: “in order to have a great city, we must have great infrastructure and to do this it takes everyone working together — communities, government and businesses”.

Following the Nancy Creek project, Mayor Franklin moved on to champion development and funding procurement of the West Area CSO tunnels, also designed by JJ&G and under excavation by the Obayashi Corp/MassAna JV and under a consent decree deadline to be in operation by 7 November 2007.

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Atlanta prepares for delivery of its new TBMs for the West Area CSO SITE VISIT REPORT: JUNE 2005

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s a follow on from the Nancy Creek project, Jordan Jones & Goulding (JJ&G) was awarded detailed design of the West Area court-ordered combined sewer overflow (CSO) project for the City of Atlanta. As one of two major projects to limit stormwater surcharge into the Chattahoochee, the West Area plan is to build some 9 miles (14.41km) of about 8.8m i.d. tunnel to intercept overflow facilities and direct retained flows to one of the City’s main treatment plants.

Table 1. West Area SCO and pumping station public bid opening result Contractor JV

Contract A

Contract B

Discount for both

Obayashi/MassAna JV

$99.7 million

$114.4 million

$3.9 million

Affholder/WL Hailey JV

$127.5 million

$146.6 million $6.2 million

JF Shea/Traylor Bros JV

$129.5 million $142.5 million $ 4 million

Kenny/Gilbert Southern JV

$158.5 million $189.5 million None

Frontier Kemper/Gunther Nash JV

A similar proposal for the East Area calls for 6.4km of 9.5m i.d. tunneling to direct flows to a different treatment plant. The brief to Preliminary Designer CH2M Hill, as a subconsultant to Program Management JV MWH/Khafra Engineering, was that the two watersheds straddled by the City’s CSO service area were to be kept separate. Proposals for detailed design of the East Area project have been submitted and the new Department of Watershed Management is yet to announce the result. As a 1998 court-ordered project, the new West Area facilities are to be operational by the penalty driven deadline of November 2007.

At bid opening in early March 2004 six bids were received for the two contracts that comprise the West Area CSO and pumping station project (Table 1). Contract A is the Clear Creek Tunnel and Contract B is the North Avenue Tunnel and pumping station.

As the lowest of the bids with a combined bid of $210 million, Obayashi Corporation of the Japanese parent construction company, in joint venture with local general contractor MassAna, the bid was well below the nearest prequalified competitor at $267 million and reportedly lower than the undisclosed Engineer’s Estimate.

$198.6 million

Obayashi exercised its significant advantage of having worked in the same area, in the same city, and for the same owner on the equally large Nancy Creek project, and with the same prime designer and lead of the construction supervision JV team - Jordon, Jones & Goulding (JJ&G).

“Having an experienced work force in our employment and ready to move to the new job without too much delay was another major advantage,” said Taro Nonaka, previously Project Manager for Obayashi in JV with CJB Contracting on the Nancy Creek contract and appointed Project Manager for the West Area CSO (WCSO) in the 90/10% JV with MassAna. “The last of the two Robbins TBMs on Nancy Creek holed-through in September 2004, and we expect to start mining with the two WCSO TBMs by the end of July and during September 2005.”

While there are many similarities between the two jobs including their lengths at just more than 8 miles each, and that both need two TBMs to complete excavation within tight court-ordered construction schedules - there is also a significant difference. Where Nancy Creek is 18ft 4in (5.6m) in cut diameter, the WCSO tunnels are bigger at 27ft (8.1m) diameter. “We couldn’t use the same TBMs on the new job,” said Nonaka. “We looked at the used market for two machines for the WCSO but 27ft (8.1m) is not a

Drill+blast excavation of the Clayton access shaft (left) and (right) lining of the Rockdale working shaft

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An order for two new hard rock gripper TBMs was placed with Herrenknecht for the WCSO contract

common diameter. There were not too many machines of that size ever built. While sourcing supply of two new TBMs, we visited the two Herrenknecht rock TBMs working on the AlpTransit Lötschberg project in Switzerland and signed a lease agreement with Herrenknecht in May 2004. Time is the critical factor for this contract and the fact that Herrenknecht could commit to building the two TBMs in nine months was a significant edge on offers from the other manufacturers. After taking delivery of the TBM components in mid-May, we plan to launch the first TBM at the bottom of the 312ft (95m) deep Rockdale Shaft by the end of July, which will be ahead of our baseline program.

“We are, in fact, ahead of schedule at the moment with the shaft sinking and site mobilization, but mining is the critical path element and we are looking for 60-70ft (18- 21m)/day from each TBM to remain on schedule. We will operate the TBMs round-the-clock on three 8hr shifts/day, 6 days/ week with a full day for maintenance on each machine on the weekends. Part of the agreement with Herrenknecht is a maintenance contract with one full-time Herrenknecht technician on each machine. We also have a cutter contract with Herrenknecht. We will pay a fixed cost/yd3 of rock excavated and they will supply all the cutter needs.”

During the site visit, the first point of contact was with Mike Robison, Resident Construction Manager for both the Nancy Creek and West Area CSO projects with JJ&G, and in association with EDT for management of the Nancy Creek project and with Delon Hampton Associates and Hatch Mott MacDonald for WCSO. Both projects are run from a single site office location at the R.M. Clayton water reclamation center (WRC). At one end of the WRC construction of the pump station is underway to accept flows from the Nancy Creek project. At the other end, construction of the new, dedicated treatment plant for the WCSO project will begin. At the WRC site, Obayashi/ MassAna is sinking the Clayton access shaft from which the second WCSO TBM will excavate 23,000ft (7km) in an uphill gradient to the 215ft (65m) deep North Avenue reception shaft. The first TBM, launched at the Rockdale Shaft will advance 20,500ft (6.2km) in an uphill gradient to its 148ft (45m) deep Clear Creek reception shaft.

“Two TBMs are a minimum requirement to get excavation of the WCSO tunnels completed and the facility in operation by the consent decree deadline of 7 November 2007,” said Ken Johnston, the City’s Project Manager for the WCSO contract. “As well as the TBM drives, the contract

Assembly of the first TBM at Rockdale Shaft, the gripper section going down with only inches to spare (right)

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includes three tunnel junctions with two adit junctions for future tunnel connections; four 40ft i.d. construction shafts; three CSO intake structures that include diversion structures, drop shafts and de-aeration chambers; four vent shafts; and a 700ft (213m) long connection tunnel to one of the intake structures. The WCSO tunnel contract includes an associated 66ft (20m) i.d. pumping station and shaft and a 24ft (7.3m) i.d. overflow tunnel and shaft.”

“The geology of the area is much the same as that encountered on the Nancy Creek project,” said Robison.

“Average compressive strengths of 25,000psi are to be expected in the predominantly hard granite and schist rock formations. The tunnel will remain unlined where possible with about 50% of the total length expecting to need an in-situ final lining to 24ft (7.3m) i.d.. Immediate support installed from off the TBM working decks, will comprise rock-bolts as required on a four-bolt pattern at 5ft (1.5m) intervals, with a six-bolt pattern in poorer rock.

In the poorest conditions there is provision to erect steel ribs. A probing facility was required on the TBMs but systematic probing is required only in identified reaches of more disturbed rock and for a total of about 1,000ft (300m) on one TBM drive and for about 1,500ft (450m) on the other.”

During the field trip, a visit underground was arranged into the completed Clayton and Rockdale TBM launch shafts and into the TBM assembly caverns and 366ft (120m) long starter tunnels. These facilities were being excavated using drill+blast and concrete lining of the shafts was also complete. “Muck haulage during TBM excavation will be via continuous conveyor,” said Nonaka. “The 36in wide, 800 tonne/hr capacity horizontal conveyors are supplied by German manufacturer DBT, with the 800 tonne/hr capacity vertical systems in each of the operating shafts supplied by Lake Shore. Our team of laborers from the Nancy Creek job totals 110 and we have 25 company management staff on the WCSO contract. We have a tight schedule and a tight price, but we are progressing well to this point.”

By December 2005, both Herrenknecht TBMs were assembled and had launched on schedule from the bottom of the 95m deep x 12m i.d. Rockdale access shaft at the end of July 2005 and in September from the 55m deep x 12m i.d. Clayton shaft assembly chamber and starter tunnel. “Once into each drive by about 450ft, we stopped excavation to install the continuous conveyor systems,” said Darrel Liebno, Obayashi Corp’s Assistant Project Manager. Since then, by end November, “the first TBM has completed 511ft and the second is just restarted after the break.”

These Herrenknecht machines are believed to be the first fitted with 19in back loaded cutters. The Obayashi team is looking to achieve an average of 18-21m/day from each TBM through hard metamorphic schist and granite rock.

Two years later in 2007, and after and eventful time, excavation of all 8.5 miles (13.5km) of large diameter TBM excavation for the WCSO control system was complete.

Breakthrough of the second 27ft (8.1m) diameter TBM holed through on 11 July, following hole through of the first on 12 April. The first TBM, achieved a best 8h shift of 72ft (22m) through hard granite rock of up to 140-170MPa strength with a best day of 147ft (45m) working three 8hr shifts/day, and a best week of 615ft (187.5m) working 6 days/week. Average advance was less than anticipated at 47ft (14.3m)/day due in large part to slow going through reaches of weaker than anticipated rock that required installation of 1,800ft of full-ring steel sets on 4ft centers or 200% more than the 650ft estimated in the GBR. The second TBM also experienced a six-week mechanical downtime to replace the main bearing unit following sudden failure of a bull gear pinion. It is believed that contaminated or suspect metallurgy of the steel used to manufacture the pinion of one of the drive motor gears caused the mechanical failure and downtime of the 8.1m diameter rock TBM. “Both TBM drives are about six-seven months delayed from the original schedule,” explained Project Manager Nonaka. “We have been given a nine-month extension by the City and are setting up to complete the lining and achieve a tight substantial completion date, with flow in the new system, of November 2008.”

Concrete lining is to be installed selectively. In reaches of good quality granite, the tunnels will remain unlined with additional rockbolts and steel fiber shotcrete as required.

“Some 10,500ft (3.2km) or 51% of the Clear Creek Tunnel needs lining, with less of the North Avenue Tunnel lined at 40% or 8,900ft (2.7km),” explained Robison.

The JV has procured two 128ft long sets of formwork from Everest to cast the 18in thick lining, some 10% of which requires rebar reinforcing. “We expect to advance at about 1 pour/day/form in the continuous lining sections,” said Nonaka, “but there are many skip sections between the 100ft to 1,800ft lined sections where we will just move the form over and over for days and weeks.”

Given the delays, the City has negotiated a one-year extension of the decree deadline to November 2008. n

Mayor Shirley Franklin joined the mid-July 2007 celebrations of the last WCSO TBM breakthrough

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Viewpoint

Atlanta’s Mayor: A politician with a vision Presentation by Mayor Shirley Franklin at the NAT Conference in Atlanta in 2004 Explanation of how funding was secured and work was initiated on one of the largest sewer tunnel projects in the USA earned the Honorable Shirley Franklin, Mayor of Atlanta, a spontaneous standing ovation from the NAT conference delegation in April 2004. It was a talk of inspiration and motivation.

Dubbing herself The Sewer Mayor, Shirley Franklin is a rare politician and her methods a credit to tenacity, innovation, and civic responsibility. This edited transcript of the speech shares the highlights.

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tlanta is currently operating under some of the most stringent environmental mandates in the nation.

Mandates that mean nothing less than total overhaul of our entire water and sewer infrastructure.

Shortly after I was elected Mayor in 2001, I did an interview and said I wouldn’t mind being known as the ‘sewer mayor’. I knew they were going to dub me something.

The fact of the matter is, in less than two years and with the help of the media, we have been able to educate everyday people on the importance of water supply and sewerage. But it isn’t easy to have a serious conversation about sewers.

Atlanta is unlike other cities. Our hills, ridges and valleys mean that long sewer lines are not practical. Atlanta has significantly more sewer outfalls than most cities our size and these empty into the city’s many creeks, streams and rivers.

We were basically a big septic tank with trees.

Many have asked me to blame somebody for the condition we find ourselves in. I say there is plenty of blame to go around over the years. When Mayor Hartsfield was leaving office in 1961 after 20 years in service, he was asked who he thought was the next likely winning candidate. He said: ‘I don’t know, but I can tell you one thing, whoever it is will have to fix the city’s sewers’. The city’s sewers were already 60 years old at that time. Now the question is, what did he do for 20 years?

He is remembered for his many innovations, but the bottom line is Atlanta for a long time has had broken infrastructure infrastructure that can’t provide safe, clean water.

Our administration has come to recognize that our underground infrastructure is a treasure, and we will do whatever it takes to protect that gold. Some say the biggest difference between the first world and third world is not food or stable political systems, it’s safe, clean drinking water.

Everyday 30,000 people die because they don’t have access to clean water. Worldwide, a child dies every 8 seconds from a water related illness.

I made it my mission when I came into office to form alliances and partnerships. I’m a proud Democrat but I understand the importance of working with those in power on both sides of the isle. I have reached out to Republican legislatures and our Republican Governor for support because frankly clean water doesn’t have a party and deserves to be at the top of everyone’s agenda.

In coming to office I found myself in the middle of a three billion dollar program of taking responsibility for decades of

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Mayor Shirley Franklin of Atlanta, Georgia (2002-2010) neglect of our water infrastructure. We are doing this with the goal of making the Chattahoochee and other rivers that supply Atlanta’s drinking water, irrigate urban Georgia and end up in Florida’s shellfish beds, the cleanest urban rivers in the country.

One of the first major acts I took as Mayor was consolidation of the department. Previously wastewater had been in Public Works, drinking water was privatized, and storm water management didn’t exist. But I thought, and the EPA agreed, that it would be more efficient to put everything dealing with water under one big umbrella, and thus the City created the Atlanta Department of Watershed Management.

And I might add, we called in some of those engineers that have been working with us in our plans for CSO improvement and said, okay, you have a blank piece of paper, how would you design a water department. They said, here are the three or four things we would do. We said, fine we like it. Let’s finalize the details. So within three months we had proposed a reorganization which in my previous life in this government would have taken two to three years to develop.

“Frankly clean water doesn’t have a party” But frankly the crisis Atlanta faced is one that cannot wait any longer. There were serious problems and boil water advisories had become routine. Our $800 million improvements will enhance delivery services greatly.

We also entered into consent decrees requiring us to fix our combined sewer overflow problems. The previous administration entered into the consent decrees in the 1990s and never figured out how to pay for it. That became my job.

That is how I became known as The Sewer Mayor.

There was much public debate about the right system to choose. Atlanta did not choose our program because it was the cheapest way to meet Federal guidelines or because it was the most popular. Rather, once we had our program, I asked Dr Wayne Gough, President of Georgia Tech to assemble nationally recognized water and sewer engineers to determine whether we had made the correct choice and indeed the committee came back and said yes. If we have Congressmen arguing about the technology, we get Dr Gough to call and have a conversation with them. It has made all the difference in the world.

So with that report we went to the City Council and the Chamber of Commerce to make our case. The 8 mile long Nancy Creek project, currently under construction, is a key component of the program and it is a great thrill to go down into the tunnel and see the progress that has been made.

If you want to get on the 6 o’clock TV news we are guaranteed a spot in the first ten minutes when we talk about our tunnels.

TunnelTalk references – Political considerations •

Alaskan Way political frustration - September 2007

•

Seattle’s bored tunnel - a story of politics - August 2011

•

USA nuclear waste options undermined by politics - July 2020

•

Cost comparison for Femarnbelt link options - November 2010

•

Passenger demand exists for US high speed rail - November 2015

•

Winning back trust in Amsterdam metro – September 2012

Probably the most difficult thing we have done • Seattle transformed by underground highway - January 2020 is increase rates. The technology is there, the requirements are there, the know-how is there, this pass. But it is worth almost $500 million over five years. and the contractors are there. The question was, do we have Our sales tax, thanks to visitors like you, is 40% transportable. the political will to actually get this done and get it funded. So It means that those who live in Atlanta only pay 60% of the after six months of public debate and internal work sessions, proceeds and people who visit pay approximately 40%. All of the City of Atlanta passed rates that, cumulatively, are a 200% that is going to accrue to the benefit of ratepayers since we increase in water and sewer rates over the next five years. I had have promised we will roll back rates as we raise other dollars. a council member ask me why I didn’t sit down with him and other dissidents, and I told him I was just tired of talking about In that regard, we are also actively pursuing federal funds. I it, and if you are tired of talking about it you are likely to say was encouraged not to seek significant Federal funds and something you can’t take back. So it was better for me to take you in the industry will know why. There are not many there! a break and come back to it and indeed on 5 January, by a 15 But we are not taking no for an answer. Originally I was asked to nothing vote, the Council adopted the most aggressive rate to lower our request. Our plan was a billion dollars from the increases this City has ever seen. ratepayers, a billion from State assistance, and a billion from the Federal Government and I was told the most we could get Part of our ability to raise the rates was that the Governor and from the Federal Government was $100 million. the leadership of the State Senate and the House General Assembly had said in October, ‘No way Jose’. They were not going to help us. Then in December, they called us and said, “Probably the most difficult thing ‘we think we have found a way to loan you $500 million over 10 years at 2% interest’ - not a bad deal – ‘and in addition, we did was increase rates” we are going to help you get authorization for a sales tax referendum so that the people will be able to vote on how Well we did something that was really not too safe in response. they pay for these rates’.

We sent out a notice to all 140,000 of our customers, a letter from me, saying I’ve done all I can. I can do no more. But you That came about because the business community stepped can do something. You can turn over this sheet of paper and up and did their own independent analysis and came back call everybody on the list. And we started with the President and said yes, the Mayor is right, and the administration is of the United States and continued with the leaderships of right, and they worked really hard to get the State leadership the House and the Senate and in the State of Georgia. to the table.

On the second to the last day of our General Assembly, at 9pm at night, they finally passed legislation that would allow us to have a referendum. That is a major step. It allows us to have a sales tax higher than any other sales tax in the State at 8%, should

Well sir, you would have thought we had opened the floodgates. People were so mad with us. But we had an obligation to tell the public those who could help. The State could help, our County Commission could help, and certainly the President of the United States could help.

So our approach was pretty bold. We didn’t leave any stone unturned. We used every strategy that was legal and ethical.

It was therefore with great pride that I watched the General Assembly make a 180 degree u-turn and say they would help us when for months they had been bashing Atlanta. It was with great satisfaction that we were able to step forward to get State help and we expect to make the same kind of case at the Federal level. When I am in Washington and I see a Congressman - probably from one of your States - they say “We know. Water and sewage.”

In 2004, Mayor Shirley Franklin and City of Atlanta Commissioner, Jack Ravan, were selected as recipients of the UCA award for outstanding planning of underground projects. The Mayor was presented with her award after her presentation by Ray Henn (left) and Tom Payton (right), the then Chair and Vice-Chair respectively of the UCA, or AUA as it was at the time.

This country’s economy cannot work if we don’t pay attention to infrastructure and I can’t help that you can’t see it!

Underground is just where it is!

The bottom line is that we have an obligation to raise the level and the acknowledgment of the importance of clean water to the future of our city and to the future of our country.

Thank you.”

The applause near lifted the roof. n 65

Accolades

In 2009, Dick Robbins received the high honour of the Benjamin Franklin Medal in Engineering. The Franklin Institute Awards are among the oldest and most prestigious science awards in the world, with winners recognized for their formidable and ground-breaking contributions in the fields of chemistry, computer and cognitive sciences, earth and environmental science, engineering, life science and physics. Robbins was recognised for his engineering development of tunnel boring machines over the decades of his celebrated career. Robbins died in 2019.

2020

2020

Throughout his career, John Reilly has been an intent observer on the procurement practices of international underground civil engineering projects.

Through his studies Reilly developed the Cost Estimate Validation Process (CEVP) that bases real out-turn cost of a project within a range of lower – when everything progresses according to plan with no, or few, unexpected changes – to higher, when the worst-case scenarios on a risk register are encountered. The concept celebrates its 20th anniversary this year (2022) and has been applied to several underground procurement projects, most notably for the SR99 Alaskan Way TBM highway replacement tunnel project in Seattle.

Having spent a tunneling career with construction company Traylor Bros, George Williamson has been instrumental in the introduction of pressurised facecontrol TBMs and high specification bolted and gasketed one-pass segmental linings to many projects in the USA, including the San Diego South Bay ocean outfall (see page 47); the U-Link of the Seattle Metro, DC Blue Plains CSO project; the Eastside, Regional Connector and Purple Line contracts for the Los Angeles Metro; and the Queens tunnels for the East Side Access railway link into Grand Central Station in New York. He is recognised also for his mentoring of new recruits and young engineers to a career in underground engineering and construction.

TunnelTalk references • • • • • • • • • • • • •

VIDEO: Face-to-Face with Dick Robbins - August 2013 Remembering Dick Robbins - June 2019 Seattle transformed by underground highway - January 2020 Alaskan Way mega-project procurement - November 2010 TBM procurement, risk and advancements - November 2020 Mobilization of Seattle’s U-Link extension - July 2010 Blue Plains tunnel teams selected in DC - March 2011 New start for LA Metro contracting - September 2005 All set for mega metro investment in Los Angeles - July 2014 LA breaks ground on Purple Line extension - November 2014 Slurry TBMs ready to tackle New York ground - March 2011 Unified USA effort to promote underground careers - January 2021 History of Tunneling in the United States of America - July 2017 (Purchase from the UCA of SME)

The UCA of SME awards in 2018 recognised three outstanding leaders of the USA underground construction industry: Dr Harvey Parker, Dr Priscilla Nelson and David Klug. David Kanagy of UCA of SME introduced the 2018 Awardees and each speaks of the importance of the recognition and their contribution to the industry.

Journalism recognized in promoting the underground engineering industry in the USA

S

hani Wallis, Editor and Publisher of TunnelTalk and a journalist in the underground civil engineering industry since 1982, received the 2006 Excellence in Journalism Award from the American Society of Civil Engineers (ASCE), Region 9. Recognition was for her coverage of tunneling projects in California that included articles on the seismic upgrade study of the BART Transbay immersed tube transit

link; the Claremont Tunnel seismic rehabilitation; the BART to San Jose project; as well as the Arrowhead and San Vicente Pipeline tunnels in Southern California.

ASCE established the award in 1994 to recognize journalists for news articles that enhance understanding of civil engineering in designing solutions for clean water, transportation, the environment and other public works.

TunnelTalk references

Journalist Shani Wallis, no happier than being on site and reporting on industry projects and developments 66

• • • • • • • • •

Nominations were open to journalist working on technical trade magazines, weekly newspapers, electronic/webbased news outlets, and radio and television channels. Through this award, ASCE hoped to engage the public in civil engineering initiatives in their communities. The Award was presented in February 2007 in Sacramento, California, at the ASCE Annual Awards Banquet. n

Seismic retrofit for BART’s Transbay tube - March 2004 Second transbay tube planned for San Francisco Bay - December 2018 Claremont Tunnel receives prestigious award - March 2009 Funding and single-bore secured for BART to San Jose - May 2018 Rethink of the BART to San Jose configuration - May 2020 Arrowhead Tunnels redesign and rebid - May 2001 Clawing success from the extreme at Arrowhead - December 2007 San Vicente stumped by tough conglomerate - September 2007 San Vicente completed and on-line - January 2011

HERRENKNECHT NORTH AMERICA

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HAMPTON ROADS BRIDGE TUNNEL (HRBT) Machine type: Variable Density TBM Diameter: 13,990mm Tunnel length: 2 × 2,440m Owner: Virgina Department of Transportation (VDOT) Contractor: Hampton Roads Connector Partners (Joint Venture of Dragados USA, Vinci Construction Grands Projets, Flatiron Constructors, Dodin Campenon Bernard)

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Application of a TBM for develo in North Yorksh pment of one of ire was the first the twin spine roads use of a TBM on demonstrated to link five coal a mining projec the significant mines t in the UK. The advantagesCA Robbins went on 5.8m diameter DY:que ofSE theSTU techni Excava Robbins TBM to supply TBMs to an estimate over tiontraditio of thenal mine opera roadheader excav non-circular TBM first eve tions thedworld half the r purpos CASE ation and for excavating over. cos also provide Most t of crea recen rectangular built STUD tly the Robbins has edevelo ting cross sectio dns. greater sec storY: ageJLE same storturbu LPG cav a new urity for thes , the ernLon age lenped s in the UK t tim acites. e vital infra inc cap don Un in the 198 y in Exc tank SITE VISIT REPORT: ludeing avati structur dergrou 0s were s on onthe faci the JUNE 1983 SITE VISIT prosurf nd Jub built at s. Ben greace and Lon litieBig ssed. Und ergroun REPOR T: MA clock unde dilee don Bri storLin e Exten tower an age r RCH 1984 dg services sion pro d the Ho or alongside to areas e mainline rai ject, live some uses of limits of lway sta d throu of sou of the Parlia the Un th and gh excit most im dergrou east Lon tions; and pa ment; create excava portant ing as nd d new ssed un don, wh tion wo well as landm metro der the rks colla system. Contr arks of ich un the mo stations til then olling ex the cit River Tha st critic pse on under had rem y, al chall cavatio the co mes fou the Wa enges ncurren ain n and r terloo ed ou togeth settleme t Heath tside the times to bri SITE VI er with row nt ng me an tec Expres SITS AN mana labyrinth hnical tro s Rail Lin d managin ging the of unlined construc D ABRI g the im k closed-circui tunn bu pro els, tion dget an DGED ject in pact of driven he Selby coal t and load Octob • Client: BAA d the M& mine complex FROM the sta beneath the in chalk some 190m ing terminals in er owner: tio Yorksh the TW 199 E for n ire was design installat er flatland on tankers at O JLE SU 4 were for rail and bank of the ed by the • Consulting Engine the south ions.

Immingham.

• Client: amon road River al UK National Coal UK Nation PPLEM Hum g as the first Coal ber, Board • Clie Board will EN Mott MacDonald

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in d on the project collapse that occurre the mind, the job in the will always focus nnelhatever jinxed ority well October 1994 achieved t: Eurotu ners: being - if iterisAuth all appears to be Designg, t Wat • Clien n remains (NCB) nt: Calor be used beginni questio d its to connect five T: JULY mined unde the nt: The ced from •petr Severn Tren Consu L) Gas Ltd . Thee of • Clie collaps separate mine sites ctor an back &then? ltant: Nation Geology Sons rgro aftersites introdu oleum 1994 AN k (TMcontrol Manager: was it not ured under liquefied - at gas (LPG al Coalund Board • Consulti Wistow, Stilling Fleet, • Contra nche Lin now why Eng s were r: G H Hill an in-depth ded portal Heathro • Construction wet fiss ) storage D FEBR The geol ng Enginee the6)inten Ma system at is aboutw in •the Riccall, Whitemoor Contra ngthat isinee the subject of Co UK. ctor: sultito ity of (p5 tiontheworks ugh the at the start Transtunnels ogy of the The Cementation facility in nelling Con vicin excava r: Geostore and North Selby.

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(Fig 1). use carri cont tingtely tion from the thorough briefing . By theconsideration. g out line All Board ainingthe e as and later ng the ess con clausesbutane, thus following n-build nt of sev n contract production millio m and the cted due pipe claDuring at nearby ersdiamand sid homoge ltgs. gs. depends 3.6k it. 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One pray it ept and with the what Of the the case vidconf servicenally booms tely tunnellin beneat tion efor4.5 ing esse 5.8m diameter d surfa ration The by depth. g machin le. to pment wou d wit onesDrilli log mad necessary its it wads Pateele inclu sion differs from l Board origi ut investiga The art JLEcompres many Robbins TBM conv larg in ngtheir and ce, con programm Site availab for slurrie and 75m hly suited UK andof site sele ce. it isstru shorson. . On from nal oil well and all equi to National Coa usindeadportals were The construction supervi with an average endentio tan never of usual toProjectsion g a methods al in a g 1979 heading readily t the cos g ethedistancethree lonofg surface e min controlling to s hig ction lieswn team is the stratum for tha was about 100m/wk. the collapse may ction store them g the e, line• Anders out durin 1km dis g through drillin som The £4.5 s. Thetype ong rig. edpos practic for ground nhillnin system ll tried and Strathclyde familiar con s alon availab t est in findibe as the refrigerate carridis The convey while flameproofed y thean areacontinued sup UK sid vals, dow of run imising arkably was going on before north in somesome els are goin d about reacave able millio borehole a le sonabl rnse,” tractorsd tank were we tes weng ticularl movem when The appoinin the ervisisinsuffi n tunn g pon explained tunnel, on the settlem whoseima deep South ibility of se inter 70m parallel, is being was awaor in the as the tunn pressure par of was g s site of tlin s it nged rem ich allowed Tunnel 1m poss TM rathe elling re but cien wate ing use set dard at ted ns, incorpo ent and geology ned the cha Pro tion acc NA ent r t rded known, said Mik r inflow epted from vessels. sink or con stan rates contract trai d on JLE tot cont than intechni be excava jec com sed a 57 x 16mm steel , nearly wh to Fairc n of , geneidrally ted using progres excavaholenel tunnels. ain the in the plan Manag on s strata, with being access socal e Smith, loug rope Titan 134 roadhe them unde pletedChe . five tend all have What had l advances greatcan plicatio cords ting h, the aqueduct rap l shal still sul ersea Ap across er forLPG but l Measure low tun s s theaper nelling as not how the work now making about is e time wed ers. red. for tiona of the lowe ader the ica Coa und to to tun To r • detail bee full eng and width orig unte allo JLE mak pres store Geo not st log sam and ially ed of of unde Construc n the 30mm ine store compen ina pre sure ’s alloew the hno init ral addi mbers half the rate of progres g enco ersagebe seep a , abelt.

French com tunnel thick scheme original. at the the grouting licenThe m/week rground pared thein largelr det thecost predicted high spe usedseve of pum sate for the tec ailecity tion. “W g are wate ceeAnders with s at Strathc methane bein cross d des projec Aqueduct while is different from the service about 50m/wk. Coal jeorpar of theon pany from contrac capa um 428 plex cha and also specified rshirallin nd breaking e t proping settlem disthe of the ancing areas ervo a proties. have been On facili designedlyde CableGeo stocconvey cannot be extract s eour Belt ed ed cave Resma rn proh gramm k, whic a maxim a maximum 8h high, the com ingt efiedt document Inignsom record The Engineer sealed, stable grou ject ofLiqu onnd ost by eve ent ma case rou orh inhas and supervise the adv t excavation where ibitiv ed North until the cross s form the s this there succ con e to grout e. this size gase h Tunnel nts tha side of s atio re g y still underg 1. Cars trol. may to be alm is a steeldrope adit connecting haveessf and to grou ensu Fig ully n. e pres of ren requ el inje Cliff. Thi tion and to The Robbin the ting had seve and t rescu pro sure store ire cur tunn e me of the the UK 7 days/week wit ft/week) buildin reinforc ctio are cons s pro bee re two oper ral TBM extensive within ich the two conveyorLPG cave ve too ineleached t shaft accelerati thods com d unde com con edion h to regim n truct venation belt On spine roads ande ns the sta unfore s and alter kespea its con r plegrou speed of thedouble shi of the cavities xity, mber, wh ground Gian the bore hole connec on clause through whic forroadhe chalk in nortwith two rns, steel inclu e into the ground trea obvious, most extensiv manin mentally ropes trac mo groutin at Sha (24h/day, maintenance working Ms used to salt see aders excava nofsits ding ater y year of 57mm st amount of over cha before arrival excavation depo conditions tme ting diamete difficulties ndwmo of the nthregim the mine one in in hern advin To start, the most ir own. l ation tion g me Oc ation has cipal usefuln s wheen e above ersthe crete seg TB aroundtua tobbut ly, is completed. the .cons ive, modific e waSelby te . The tingce, forspine engineer. r supporFran the expected Two effe nt er finding for a lightwe ess ove is the ight the cave es: advance a purp permeatio thods use the prin the rec downtim s the the six we service lted con ble truct cons1in-thic ssure comple chines. Similar Associate deal with ose-built1994 of suita clearly most expens Theis Wistow re bei geol rns onroads ionngof wate ctiv . 8,036m on three stag r the belt. The ulting k d on ogycollap NATM the site of non-bo the 60mmine came marine n gro steel ropes d cont undergro ry proby and pre ck unrelated tunnel; and and se wate is done in ma r galleove JLE inc e eek nel of o.d racts are easy each of the strengt launch uting, scope of works spliced together noAt und exc online in April cons a fully gramm sages r curtainsnegotia task tunnel driving the mu ted.” ries abov faciliava water. This , but con lude itsAirp to truct hen ty tion final the e, l to the original ersea tun e was 179m/w to sta formionanof endless the Paterson es a new LPG include ort, as is wo te 22km and 18.77km 14.5km between Sou Exp advance of cross pas o had to share rkth Killin length, curren River Hum cofferdam built in and radia bilise expl the rope jetty ress Ra “The Settle and com loose water comple th. lined und rag caverns. ing at each m t, Heath of the gholm or grouting in geollongest ber, d:convey an the are built; als side. will on the and be diameter x 30m deep me, il Linkaine ogy mus nel sou At rall ave advanc 17.36k airport pensation bearing enneith row r galle edi of tits wate g ducts enough toimm tun connect the and pipelines which t coerntr as the rings kindcom completed. ate and grouting nor be Area (CTA of the Ground with the the effe tunnel, rtal nel in l best ove rine running tun dern slurry and evin ting operatio gro been es po Termina ry reli gro pro grou n in allow Jub will und is has Europe tim to pete ol facili Central expe uting for cts mo also of a . proextensiveresponsib ilee ntjec , ty to the Con ma rtal cted vem dings. the lining rised rtation to almost totally to be nece ent ind side, mo cour ject tea excavatio intercept of predicted lenreactio t. As Becbee mitigating the UK ause from po oco refinery n one transpo ning tunnel hea rk which ls 1, 2 and 3) uced by ssary. grouting after itsse con the mor French B) pressu nel the Termina m vol and the of n, geol (EP gro the of Tun um vol e e the the extent ogic wo el excava und mo run the siteJLE On untarily the requirement, tractors limited the anc ss areprojectimpo mostalcritprop vement e losses and marine ass and remove g Chann drives ins Wavs mining A Titan E20 ical erties oftion has ral cro the morto ssure bal terloo TBM orttrucbay stop NAsupp s as the team. rtant lem encomp ted ben so road ground. Only by hand secutive 5 roadhead ny late cerns for 53km lon , a geotcon and head The earth pre Compe er omicTM the y occur.

Lonedonecon been eath som ducts echn of the the ma integrit Four con firms that bid the job, MowWork collapse and the disturbed huge excavation er excavatin work at has the estaeblished, Line • The , run Since Bridge they introdu ningical piezome plished re relief and saf of the old g the 9m t er. al section equipped ction imp as it doe Compens nsation gr to review ters ortant pressu accom wideprogres g at the edge of this nels. ety ofof the TBM, Of the eigh to measure lowest tend est, hist with the the s x 1km Geologic outing 5m high ation was standin sofrates es and the wo NATMin ated. "The upper orically bored tun s and the second ground is subject and pre theing, stigiou a com South groutin head passag rks.have wo 1981 and Tunnel most for JLE top its scale be appreci e main won with wate s, rk que er could Ab g and with ed thre r are had ple hni s. temb out ground as of Lon visible ban to the x exe is prin the at that Sep ing tec limitation manag ure in four year soft water-bearing linking rcise d outer cipally time and been com NATM don, started in plete em pleds tolerances most stringen ed survey ployed to ens 1.2m four l and flint com to 20m through tedof mar the in mu work to beand advanc a tun t damage and stabilized by decisio ent and copresenteve only one dingdeepdesi rescue gnedshaft restarted although rev lti-level nelling pro the centra the del l inrthe • The ce systems emdiamet befchal n-m ope x 30m gravels is supported wasshaft, er hea k on ised ore imp ay had access k ose in due 60mea tunnel er plan dan of the provided aking based rative all-par four portals piles which interloc fact l 19m Mowlem guiTrace the Assess ject in the city. a dam d on . Inorigina Fig 1.

The diamet undersposed fromnt stages of ers diameter Secant ty the sea on aging effe course, pre on info ments differe tunnels by ext under the six head d Alan Powderham, main superim instrum were of under the nch service rmation dicted thatshafts Compens ct on ens all of which access drive the thclyde road r Steel 1.06m centres," explaine entatio and 1mm set all buildings wit ly meet platfor m tunnels, on the the ation gro n and ive geotechni the Fre erson Stra actual the Foundations analysi and outer hin the tlement didrse 12.4km concou UK andAquedu using And ct mm uting arr s. “Th cal and Grosveno C in Managing Director of ed 350 the the nald com collaps ham in con of und MacDo n works Mark put on e al Mott with tou in ays und of erground ctio when Harris, ingt s Port r juntion Cars excava mounted km hea a Directo aim,” explain er-based er the Geotechnical Division started at on dings wa l. route defi along Westm of the 10.5 ed Da r's representative Tunnelling r the prin B and D in rine tunnel nes a on leve sections inster are vid cipal geo of the compan and the lead designe the ma d shields. 1982, and at Portals 60mm convened and cross a install y GCG on com technical nts of ate l.

Solutions Team line and uary gitudinal d me cre Apri Febr Lon in so-calle ed as ish pen 2.

A ich r the from five Fig adviser sation e, in establ finally at a side wh g the collapse to enginee groutin early stag tempo lk cliffs 3 March, and • The s on the UK g, “is to to JLE s, immediately followin rary gro . "The ded at an ite cha ding m keep the lagoon uting sha nd condition a safe and economic way forward It was deci the wh nel hea 5 million icted grou foot of fts ted by 900mm rvice Tun some 3.7 and tightly view of the pred comprehensive plan at the Clay below is suppor UK Se site for all a for the vation,London which step in disposal what is an sm acture to formulate the method of exca Withdiameter contiguous piles in manuf . . h 20m below, the of muck TBM in anent lining incorporating rking site factories in bot and continue a further from, perm wo at d beam Howden main and h ort confine loyer, the "A substantial capping roof supp nt casting usands of hig 79Secant piles. of the Emp e collar nt segme ort concret re tho rigid eme a Rep we The ere • the agre surface forms ments of CIRIA es wh tices’ground r. lining seg UK factory recommendations countri Contract Prac oachlinking all the piles togethe tunnel The ial - Improved appr y ideas were precision at high rats.

‘Tunnelling a potent "Originally, recover the general ed ting a large ments. day produc followed and Grain had ract docu ively based on excava nts per 55 were Isle of Fig 1. Plan of the in the cont segme said Powderham. el were toinstinct on the 2,7 Gascoigne Wood incorporated of the tunn of about 65m x 65m," of 1,152 required 4,4 drifts and the five mine ugh sections rock, the need forbox output the Altho shaft sites; ed duc rs. petent Inset: Fig 2. Main near the and pro within 3.5 yea expected design features driven in com on of was be ort ng nts segme now goi and lengths immediate roof supp allation ts inst uni er of • The thousands and oth , track ling many cab trical of elec 37 42

REPORT

S CA SE

Fullfacer vsKillro ingholme rises : er: head Britainad Heathrow and shines ’s first un ire m t: the m c fro an dergroun u d in t ve e h stm u q en d liquefie ig re t A s tu in spee dn A into d d gas st inst na hg inin Jubile T Ceal rs Man ag a n n u T e Line ore l e W n n a Ex Ch Triump tension: hs and W W F trib

UK F OCU

in October 1994 Express Rail Link on the Heathrow al prosecution ations excavma world. The crimin de during NATM station ision s and across the the UKlds Collapse of the r the works and ry in how dec ling indust of tunnel in the shielater, after working on to recove for the erience ations dheadersfour years nt exp t ramific impac the roa a salie high engineer had that -build was anticipated ct ed a design than its edu dict er ed and aqu of the vidproctor re wat ject pre The procontra the trial and Carsington in injury.

98, for to mo drill+blast.

19 Its rock insult long or ding ts. der km added t, bid ing har es jec the d min victors compre ounts pro trac when lete t projec DY: The 10.5 wrong.

Con l ser p large am were righagainst rs and turn to han c rai truyctu CASE STU ly The ras ous as. s air to kee istminf to publi re me go seri ga canop roadheade hmark ened compressed befo Chr designan upnctheir d as be ed under of future es the hillsgide tondgive letedld be on 1996 was advanc ms, sta four driv d fundin the shield, l, comp wou tion ane VISIT REPORT: JUNE d proble roadheaderSITE out of Tunne izaed thre cu mente t its forc organ annel ll doface, which kep we nning, The Ch its ng pla Y: as aini STUD trol. ovative as well rem CASE under con the inn cesses, of water del for tion suc kes. role mo construc similar mista RCH 1983 nding oid outsta will av REPOR T: MA others SITE VISIT which

CASE STUDY: