Boston Big Dig - A Case Study

Direct by Design

Underground in Actio U

Special Edition Case Study

Boston Big Dig Project

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Direct by Design FROM THE EDITOR’S DESK

Control of mega projects

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eplacement underground of the double decked elevated highway through the heart of Boston was a tremendous undertaking. The highway, known as the Green Monster, had dominated the city for more than 50 years and getting it out of sight was the largest underground engineering project in the USA to date in the late 1990s/early 2000s.

To became known as the Big Dig, the mega multi-billiondollar project was based, for the most part, on a cut-andcover operation directly beneath the alignment of the elevated viaduct, an operation often described as openheart surgery through the center of the city. The design and construction phases of the project - together with the two immersed tubes on the masterplan alignment, the jacked boxes under the South Station railway tracks and the underpass of the South Station Subway Station - are chronicled in TunnelTalk Archive articles of this Case Study Special Edition. The articles are based on visits to project management offices, interviews with senior design and construction managers, and visits to construction sites once the works began.

As well as the decision making that framed the design and method of construction for each segment of the mammoth undertaking, the archive articles review the concerns and causes at the time of the project’s ballooning costs.

The Case Study articles also report on the many safety and construction quality issues that plagued the as-built underground infrastructure once opened to the public and in the first years of its operation. It is these aspects of mega project management that most lessons are to be learned from this particular mega project.

Many might say that the fundament lesson to be learned from the undertaking is to build it right first time. The traffic corridor through Boston has, effectively, been built three times. First by demolishing parts of the urban fabric to expand traffic lanes on the surface; then to build extra traffic lanes up on a steel elevated structure that would become ugly, severely congested, and have a limited life span of 50 years or less; and then finally where it should have been from the start – underground.

But while we cannot diss the civil and planning engineers of the past, who had to produce their solutions from the resources available at the time, there are many engineers of today looking at the same dilemma of what to do with elevated highways that everyone wishes were not there. In Seattle the answer to replacing the double deck elevated Alaskan Way SR-99 highway was the mega TBM bored tunnel solution. TunnelTalk reporting on that project will be the focus of the next Special Edition Case Study.

Underground in Action U

For elsewhere around the world engineers are considering reconstruction underground of other elevated highways that cut across the city of Toronto in Canada; run above the Sydney Harbour foreshore in Australia; and fly over the streets of Hammersmith in London. What might the engineers of today decide is the best solution and best way forward for these urban reconstructions.

Objective achieved. Where once highway traffic ran on the double-decked elevated structure through downtown Boston, it now runs through a route of underground infrastructure

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Photo by Rene Schwietzke. Front cover photo by Tyler Tomasek

Shani Wallis, Executive Editor

Highway in the sky to sink out of sight

CASE STUDY: A complex construction program to replace the existing Central Artery viaduct

highway into an underground alignment directly beneath, together with a new 1.2km-long, four-lane immersed tube road tunnel across the harbor, are central to a comprehensive restructuring of the highway system through Boston. In 1987, with preliminary design well underway, the project was estimated to cost a total $4.4 billion and construction was expected to be at its most concentrated between 1992 and 1996. In this Case Study we review reporting of the project through the 1990s and early 2000s to know of the actual outcome of these aspirations.

DECEMBER 1989

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SHANI WALLIS

wo major interstate highways intersect in Boston city center. The east-west I-90 links Boston, Massachusetts, with Seattle, Washington State, on the other side of the country and the north-south I-93 connect the States of Maine and Massachusetts. Through traffic on both used the 1.5 mile (2km) six-lane Central Artery elevated highway built in the early 1950s to cope with the increased interstate demand.

All I-90 and I-93 through traffic used the Artery as part of its journey. Local traffic used it to feed into the Sumner and Callahan immersed tube road tunnels that were opened in 1934 and 1961 respectively to gain access to east Boston and the city’s international airport (Fig 1). In addition, the 30-year-old steel and concrete structure would soon be needing costly renovation. If nothing else, it would need new road decks within ten years.

At the time, the viaduct was considered a masterpiece of civil engineering. Designed to carry a maximum of 75,000 vehicles/day, it was seen as an innovative method of providing a major six-lane highway through a dense urban area without disrupting local traffic.

The basis of a strategy finalized in 1985 to cope with these problems was to separate the interstate highway traffic. I-90 traffic not destined specifically for Boston would by-pass the city and pass under the harbor in a third immersed tube road tunnel. I-93 traffic would continue to pass through the city but on a new cutand-cover underground highway excavated directly underneath the existing viaduct. Once in place, the old structure would be dismantled and replaced by some commercial development and open parks and gardens.

For some 35 years the viaduct served its purpose, but by the 1980s it had become an eyesore to the more environmentally aware citizens and was notoriously dangerous. In the late 1980s the viaduct carried about 190,000 vehicles/day. Congestion in the rush hours was chronic, and with 18 on- and off-ramps over its 1.5-mile length, it had the highest accident rate of any urban highway in the USA.

The client for this ambitious project, the Massachusetts Department of Public Works (WDPW), set a goal to have the I-90 third harbor immersed tube tunnel in operation

Fig 1. A network of new immersed tube tunnels and cut-and-cover work will transform traffic management in the city of Boston and replace the elevated Central Artery double-deck city center highway into an underground alignment

The scale of the undertaking in Boston is truly impressive: • 161 lane miles (258 lane km) of new highway in a 7.5-mile (12km) corridor, half of this built underground • An 8-10-lane limited access underground expressway to replace the elevated I-93 • A new immersed tube across the harbor to Logan Airport for the I-90 • The world’s largest tunnel ventilation system • Four major highway interchanges • 5 miles (8km) of 120ft (36m) deep slurry walls installed 10ft (3m) in each panel • More than 13 million yd3 (10 million m3) of excavated material – two thirds trucked to landfills, the rest barged to cap an old dump site on Spectacle Island • 3.8 million yd3 (3 million m3) of concrete placed • 29 miles (46km) of utility pipelines, owned by 31 separate companies, relocated • About 150 cranes in use project wide • At peak some 15,000 people (4,000 construction workers) employed on project business by 1994 and to have all traces of the old Artery viaduct taken away by the end of 1998. To get the program started, the MDPW engaged the Bechtel/Parsons Brinckerhoff (B/PB) JV in 1985 as the management consultant. The two had worked together several times including on the San Francisco BART project in the 1960s and on early development phases of the Washington DC Metro in the 1970s and 1980s.

“Management of the project, which includes preliminary design, management of consultants engaged to complete final design, preparation of construction bid documents, management of the construction phase, quality control, control of schedules, and settlement of claims and extra costs, is based on a rolling three-year series of contracts,” said Mel Mirsky, B/PB’s former Project Manager. (Don Marshall was the current Project Manager.) “We have completed the first three-year concept feasibility phase and will complete the next preliminary design threeyear phase by February 1993. It is then usual for the same management consultant to continue through the construction and commissioning stages although the MDPW has the power to change this.”

engineer for final design of the I-90 immersed tube tunnel, the first of the major detailed design contracts to be awarded. Parsons Brinckerhoff, designer of several immersed tube tunnels in the USA, is disqualified from bidding for the final design as it is part of the management team.

The preliminary design for the immersed tube was based on the USA full binocular, steel shell concept with an inner concrete lining. Twelve 98m long x 24m wide x 12.2m high elements would comprise the underwater section with each element carrying four traffic lanes, two in each direction. A cut-and-cover approach section built within slurry diaphragm walls and cofferdams at each landfall will give the tunnel a total length of 1,200m.

The immersed tube elements will sit some 24m below sea level in a 12m-deep trench on the harbor seabed with the top of the tunnel about 2.5m below the surface once the trench is backfilled. The geology under the harbor on the alignment is highly variable, ranging from argillite bedrock to soft silts and clay. The argillite will require underwater blasting to create the trench while some of the clays may have to be removed and replaced with more competent foundation material.

Although the project is having to be programmed on a fast-track schedule, construction work cannot begin in earnest until the State and Federal Governments have approved the client’s Environmental A binocular steel shell immersed tube will take I-90 traffic across the Impact Statement (EIS), which considers the harbor to the airport and beyond practicalities of the project and the steps taken to minimize the undoubted impact construction work will have on the public, both commercial and private. The MDPW submitted the EIS in 1985 but the Federal Highway Administration, which will help fund the project, felt that a number of issues had not been addressed sufficiently. ‘‘We have since examined the outstanding issues and revised other points to present an altogether better approach to the project,” said Mirsky. “The supplementary EIS will be submitted by December 1989. When it is approved, we have a green light to go ahead.”

Immersed tube first

In the meantime, in October 1989, Sverdrup Corporation was appointed as consulting 4

Following a 12-month final design period, tender documents for the $170 million immersed tube contract were to be released by January 1991 with construction work to begin by May 1991.

In addition, the new I-90 route includes a $250 million multi-level interchange at the junction with the existing I-93 highway and a new 2.5km-long highway from there to the harbor.

En route, this highway must cross the 1.8km long x 270m wide Fort Point Channel. This crossing is also designed as an immersed tube which is made complicated by the two transit tunnels of Boston’s metro system that pass under the Channel just at the point where the immersed tube must cross.

These bored transit tunnels on the MBTA Red Line are on 9.1m centers and are about 6.1m below the bottom of the Channel. They were built through till and clay under compressed air in the early 1900s and are lined with about 75cm of unreinforced concrete cast directly against the ground. To protect these old but vital transit tunnels from the weight of the new highway tunnel, the immersed tubes will rest less than 1m above on a bridge of piers founded deep into the glacial till or bedrock on either side.

Ten 92m long x 7m high elements will make up the new immersed tube road crossing and these will range from 15m to 43m wide, depending on the number of lanes within. These elements are designed as precast concrete rectangular units rather than binocular Fig 2. Construction sequence of the 8-lane cut-and-cover Central Artery steel shell structures to minimize their replacement. Beams between the slurry walls will hold up the elevated structure height. They must sit above the existing while construction continues underneath. Work on the new highway will metro tunnels but not obstruct the progress without disturbing traffic on the viaduct or on existing surface streets Channel’s water flow as there is a major Cut-and-cover flexibility sewer outfall upstream of the crossing. The water of the Channel is used also in the cooling system of a large Once the harbor tunnel is opened in 1994, and I-90 factory on the up-side of the new immersed tube. through traffic is bypassing Boston city center, work on the I-93 to replace the elevated Artery viaduct can begin.

The basic principle here is to undermine the existing Because the larger units will not pass under the existing structure and excavate more than 14 million m3 of muck bridges across the Channel, they will be cast in the to create a cut-and-cover highway directly beneath (Fig 274m long x 91m wide cut-and-cover approach section 2). Besides being a demanding construction project, it will on the east side. The basin can only accommodate six be an immensely complex logistical exercise, with such elements at once and will therefore be breached and heavy earthmoving works taking place in the heart of a rebuilt to provide two element construction phases. This city more than 300 years old. may delay the Channel crossing opening until 1994.

This will not affect the 1994 planned opening of the new harbor tunnel but its traffic will not be able to drive First, the Artery and the surface roads underneath must directly on to the I-93 until the Channel crossing opens. remain in use throughout the entire operation. The 180 Extensive railroad yards and other obstructions prevent columns supporting the viaduct will have to be individually the approach section on the west side of the Channel underpinned to hold up the structure as excavation goes being used as a casting basin. on underneath it. “We will in effect have to build a bridge to support a bridge,” said Bill Twomey, Project Manager for MDPW. Another complex section of the new I-90 route is at the west end where the underground alignment must Boston’s geology is known to be highly variable, with the pass under the many tracks of the approach to the water table rising to within 3m of the surface. In addition South Station railway terminus. An innovative box to highly permeable sands and gravels, organic silts, jacking operation is being developed for this section of silty clays and tills, there is a great deal of fill material laid the project.

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The conveyor system may run the length of the cut-and-cover excavation and will lead to four barge docks along the waterfront.

Muck will be discharge into waiting barges and transported to Spectacle Island. This uninhabited island in the harbor has been used primarily as a dumping ground over the years. The clay muck from the project will be used to cap the island and reclaim it as a public recreation area.

“A key to the success of this project will be constant tight control of the excavation phase,” said Burt Kassap, constructability expert and now Construction Manager with B/PB. As a result, the construction sequence is to proceed with utility relocations, installation of temporary roadway deck Fig 3. Pipe jack forepoling is suggested for the I-90 under passing of beams, underpinning structures for the the South Station underground metro station existing elevated viaduct and support of any additional utilities from the deck beams. down during extensive land reclamation projects in the Timber or precast concrete decking panels would be past. A large percentage of the cut-and-cover excavation placed over the deck beams to reinstate the surface will be up to 35m deep through this fill material. roads and sidewalks with excavation of the new tunnel Competent argillite bedrock lies about 40m below the continuing underneath. Traffic on one side of the Artery surface on average, but this too is unpredictable with will be diverted into the new tunnel in phases once it troughs as deep as 75m and peaks rising to within 5m of is completed and a similar operation will be carried the surface. More than 2,000 borings have been taken out for the other side. Only when all traffic is diverted to help identify the complex nature of the ground. underground will the old viaduct be dismantled.

In depressing the Artery, there will be 22 on- and offramp connections with the surface roads. The minimum 40m wide, eight-lane cross section increases to up to 65m wide to accommodate these on-off ramps. Cut-andcover excavation between deep slurry diaphragm walls is the method chosen to excavate the varying crosssections and the sloping levels of the ramp road decks.

About $300 million of slurry wall construction is required throughout the project.

The use of concrete slurry walls is expected to allow excavation in this waterbearing strata to proceed without risk of settlement damage to the many modern high-rise office towers and historic buildings adjacent to the excavation route. Many of the older buildings along the waterfront have recently undergone expensive refurbishment. Controlled dewatering from within the slurry walls may also be necessary in areas of more highly permeable soils. It will be carefully monitored to minimize the quantity of water removed and recharging wells will be installed where necessary.

Ground treatment with grout injection may also be used to improve soil conditions. Controlled blasting and hydraulic breakers will be used to break out any argillite intrusions, while excavators will make short work of the softer materials within the slurry walls. Needless to say, an extensive instrumentation and monitoring program of surrounding buildings will be a significant part of the construction phase.

Removal of 14 million m3 of muck from the city center is a particular challenge. To reduce the hauling of truckloads of muck on the city streets, contractors may be specified to use conveyor belts which will be attached to the superstructure of the Artery. Muck will be crushed to maximum 6in pieces and lifted by vertical conveyor on to a special tube type conveyor that will roll itself into a pipe and roll out again at the discharge point. This will avoid the mess and dust created either by trucks or on a flat conveyor haulage system.

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No bored tunnels

Although this is a major excavation and tunneling project, there are no bored tunnels as such. It is impossible to tunnel under the Fort Pont Channel because of the presence of the old metro tunnels and a bored tunnel under the harbor is not considered a feasible solution because of the poor soils within the alignment.

A bored tunnel for the replacement of the Artery was rejected principally because of the many varied cross sections needed to accommodate the on-off ramp sections and because the geology under the city is considered too unstable for safe tunneling.

The one section where a bored or mined tunnel is a possible solution is at the north end of the project where the four-lane I-90 roadway must pass under the South Station underground metro station (Fig 3). The bottom deck of the station is about 17m below the surface and the bottom of the 8m-high road tunnel will be about 30m below the surface, leaving only about 5m between the two.

Fig 4. A multi-phased NATM alternative is suggested for the metro station underpass

The geology here consists of about 6m of fill material with 27m of Boston Blue Clay on top of the argillite bedrock, and the water table rising to within 3m of the surface. Several methods of tunneling this section were considered by B/PB, including shield-driven tunnels, ground freezing and jet grouting, but all have been rejected for a pipejacked underpinning scheme. Under the scheme the metro station will sit on the roof of jacked pipes, which in turn is supported by girders transferring the load to piers founded in bedrock (Fig 3).

the pipes cast into large transfer girders cast within the hand-mined tunnels.

Once installed, the road tunnel will be excavated underneath. Non-explosive rock splitting is likely to be required to excavate the bedrock as it rises into the tunnel line.

Although this is considered the most viable method, it is time-consuming and expensive. There is also the possibility of ground movement around the pipes as the headings are hand-excavated.

To do this, one possible method is to first construct four access shafts at the corners of the station and connect them crosswise by a hand-mined tunnel which will form a jacking gallery on one side. From here eighteen 1.2m long x 1.5m diameter pipes will be jacked 20m through to the reception gallery. These will then be concrete filled and post-tensioned, with the ends of

One other method given serious consideration for this section by B/PB was a mined NATM alternative with appropriate soil stabilization. Design engineer Gerhard Sauer of Austria submitted a feasibility study for the scheme and proposed that the tunnel be excavated following the multi-phased, side wall drift approach (Fig 4).

Construction of diaphragm walls amid traffic diversions ahead open cut highway excavation

Ventilation considerations

When opened, the new underground highway tunnel will operate a fully transverse ventilation system, with fresh air being continuously fed in under the road deck, entering the roadway from vents on the left side, and exhaust air will be continuously withdrawn into the space above the suspended ceiling through ducts on the right.

There will be seven ventilation buildings along the route, each housing 26 fans. To reduce the visual impact of the buildings on the environment and to minimize the noise, the equipment will be installed up to 100ft underground and the buildings on top will be camouflaged to look more like city buildings. Some 27 million ft3/min of fresh air will be forced into the long highway tunnel complex at all times.

Photos by Vanderwalker. Illustration by the Project’s PR Office

In total, this massive civil engineering undertaking will involve 15 major structural elements which will be covered by 15 design contract packages and 66 construction contract packages valued at between $75 million and $150 million. All final design contracts are expected to be awarded by December 1992. Smaller contracts to relocate services have already been awarded but the major construction contracts are expected to be tendered for and awarded during 1991-1992. By about the summer of 1998, after years of intensive earthmoving works in the very heart of their city, Bostonians and visitors to this historic city, will enjoy an environment that is completely transformed.

A concentration of city center ground engineering JUNE 1999

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y the end of the 1990s, construction of the new highway network across Boston was in full swing.

With it the citizens of Boston and its visitors have had to accommodate heavy construction equipment, heavy construction activity and multiple traffic diversions.

Given the scope and the location of the work, it should be no surprise that approximately $3 billion of the $10.8 billion project budget is being spent on project mitigation. At about a third of the project cost, this could be considered a benchmark for keeping a city’s routine intact and the general public in support of major city center construction.

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Mitigation covers a host of different requirements from noise and dust control; to the cost of work hour restrictions; traffic diversions; pedestrian management; utility diversions; an intense instrumentation and monitoring program of adjacent buildings; environmental concerns; and the maintaining of traffic on the elevated highway as excavation takes place directly beneath.

“At the moment the project is spending about $3 million/ day,” said Terry Brown, the project’s Public Relations Manager, “and despite this peak of activity, the city’s economy is thriving. When we started the fear was that the work would effectively shut down the city. That just has not happened. The city is doing well, mainly because the USA economy is doing well, and we have not stood in the way of this. Office and hotel occupancy is at historic highs, the price of office and residential property has increased, tourism has not dried up, and despite all, access to all businesses has been maintained - and traffic is moving. The promise we made to keep the city operating we have kept,” he said. “We are now 50% through the 14-year construction period and we have started phased opening of the completed sections.

The I-90 Ted Williams immersed tube link across the harbor to the airport was opened to commercial traffic in 1995 and will open fully in 2001 when the highway connections are complete either side; the Charles River bridge is schedule to open in 1999; and the I-93 underground Artery will open in 2002 northbound and in 2003 southbound. By 2004 the elevated structure will be gone and the project will be complete.”

Cost

According to public relations information, the project’s massive budget has remained steady since 1993, when the final scope was set and the budget was approved at $7.8 billion (excluding inflation). The current $10.8 billion cost is the forecast completion cost in 2004 and includes inflation. It also includes a cost anticipation increase of $400 million which is not unrealistic given the scope of the job. Construction started in 1991 and completion was extended by a year in 1993 to 2004.

The construction management and design contract was the first awarded in 1985 to Bechtel/Parsons Brinckerhoff.

Design under this contract was taken to 10%. Detailed designers then completed section design and prepared contract documents. More than $500 million of design work is now 99% complete and value engineering alternatives have saved more than $500 million.

Bechtel/Parsons Brinckerhoff continued its role by establishing field offices with resident engineers and teams of inspectors to supervise all construction contracts.

Panel excavation for the diaphragm walls

Fig 1. Plan of the major construction works to transform traffic movement in, around, and through Boston

Client for this major highway project is the Massachusetts Turnpike Authority. Of the $10.8 billion project budget to 2004, 60-70% is funded by the Federal Government’s Transportation Administration and the remainder by the Commonwealth State Government of Massachusetts and the City administration of Boston.

Remarkably, for a project of this scale, there have been few incidents or accidents. There was a slope collapse in Summer 1998 with minor consequences and there has been unfortunately one fatality on pile driving for the Artery underpinning. The Director of Safety is an engineer from Bechtel and the program is being overseen ultimately by OSHA, the Federal Occupational Safety and Health Authority. The project has a single $800 million wrap-around insurance policy underwritten by AIG in New York. The policy has a 55% loss ratio and will break even at a 45% ratio. The fund will remain active until 2017 and the policy is currently operating on an anticipated loss ratio of about 23% which illustrates the effectiveness of the on-site safety regime.

Relocation of the 1.5 mile (2km) long I-93 highway underground is divided into several contract packages.

Modern Continental, in joint venture with Ohayashi for two of the contracts, is working on the longest stretch of the work in the downtown area, completing contracts 17A1, and 17A2 and 17A9 for a combined contract value of $650 million, and Perini/Kiewit/Cashman have a $313 million contract for the 11A1 section. In addition teams of specialist subconsultants including Haley & Aldrich, Jenny Engineering and GZA Environmental, are providing geotechnical, civil and environmental engineering on this sensitive and complex piece of urban construction. At all times the elevated highway must remain in operation.

After installing the diaphragm walls to bedrock, steel beams are placed at the surface to underpin the elevated structure. Decking over the excavations maintains surface traffic. As excavation progresses massive steel girders

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brace the excavation walls. Once traffic is redirected underground, the aging, steel elevated highway, built in the 1950s, will be demolished and replaced with 30 acres of parks and gardens.

Red Line underpass

A most delicate section of the I-93 Central Artery relocation is the underpass of the Boston Subway Red Line underground South Station. At some 100ft (30m) deep this is the deepest part of the lowered highway and the highway’s roof is the bottom of the subway station. To safely underpass the station, and the new MBTA South Piers Transitway alongside, section designers Seelye Stevenson/Deleuw Cather, with specialist geotechnical subconsultants Haley & Aldrich and project construction managers Bechtel/Parsons Brinckerhoff, decided to first underpin the station with a subsurface bridge of concrete filled galleries. This would transfer load of the station to the bedrock and allow the highway tunnel to pass under.

The South Station terminal building and two adjacent high rise office towers must also be protected from the construction influences. Therefore, prior to building the galleries for the bridge, Perini/Kiewit/Cashman, contractor for this C11A1 section, engaged specialist subcontractor Hay-ward Baker to carry out a comprehensive program of ground treatment.

This involved injection of some 80,000 litres of sodium silicate grout and AC400 low viscosity acrylate grout to improve the stability of the fine clay and silts, and control groundwater movement. From two 15ft (4.5m) diameter slurry wall shafts, the top two 15ft (4.5m) diameter x 98ft (30m) long galleries of the support bridge were hand mined and lined with steel ribs and steel lagging. From these Hayward Baker installed vertical tube-a-manchette arrays for precise injection of the chemical grout. Seismic crosshole measurements during installation of the tubea-manchette pipes assessed the density profile of the soil before treatment, and monitored improvement as the grouting progressed.

A binocular steel shell immersed tube will take I-90 traffic across the harbor to the airport and beyond

star, comprises twelve 80ft (24m) long steel immersed tube elements. Work on this first element of the Boston highway improvement program started back in 1989 when the Morrison Knudsen/Interbeton/J F White Joint Venture won the $1.3 billion contract. Designed by Sverdrup Corporation, and under project management control by Bechtel/Parsons Brinckerhoff, the binocular shaped steel elements were built in Baltimore and towed around to Boston Harbor.

At each end, the immersed tunnel is connected to the landfalls via the widest and deepest circular cofferdams ever in North America. The south end cofferdam now accommodates the tunnel’s ventilation building. By 1999 the tunnel carried 25,000 vehicles/day. When fully opened traffic will increase to some 94,000/day, providing much needed relief for the Sumner and Callahan immersed tube road tunnels and diverting a great deal of traffic from the downtown area.

Fort Point Channel crossing

The immersed tube crossing of the Fort Point Channel comprises six cast concrete elements of up to 420ft (127m) long. Here again, rather than being straightforward, the immersed tube elements sit just 6.5ft (2m) above the old tunnels of the Boston Subway Red Line that runs the length Once completed, the two access shafts were extended of the Channel (Fig 5). To protect these near 100-year-old to 120ft (36rn) deep and the lower three hand mined subway tunnels, Modern Continental, stacked drifts were excavated.

Fig 5.

Complex set of construction contractor for the job, has installed Concurrently the galleries of the methods to cross the Fort Point Channel a series of about 110 6ft (1.8m) cross beams were excavated diameter x 120ft-160ft (36m-48m) and filled with concrete and post and under the surface tracks of the South Station railway terminus deep bored piles to create a bridge tensioning cables. On completion over the subway and on which the of the support bridge, excavation of highway tunnel elements will sit. the core will begin. This is scheduled Under separate contract Modern

by Perini/Kiewit/Cashman to start in Continental completed construction early Fall 1999. of the 1,100ft long (335m) casting basin on the east side of the channel At another point along the Central and has nearly completed casting of Artery route, in contract 17A9, the first four elements. The casting Modern Continental/Obayashi has basin, which will eventually be built to overpass the Subway Blue Line into the cut-and-cover continuation tunnels. This is the highest point of of the I-90 to the Ted Williams Tunnel, the subsurface highway and the roof is expected to be breached in Fall of the underground freeway will be 1999 to sink the first four elements the base slab of the subway tunnels. and then rebuilt and breached again in Spring 2000 to place the last two.

Third harbor immersed Detailed section designer for the tube crossing crossing is Gannett Fleming/URS/ TAMS with specialist subconsultants The Ted Williams Tunnel, named after Acer and Shannon & Wilson.

Boston’s famous Red Sox baseball 9

Tunnel jacking

Between the South Bay interchange and the Ted Williams cross harbor tunnel, the I-90 passes under live surface rail tracks into South Station terminus. A connection to the underground I-93 has to make the same passage. Instead of undertaking a slow, costly and delicate operation to move each set of tracks one by one and build a cutand-cover section from the surface down, specialist designer Hatch Mott MacDonald, to section designer Maguire/Fredrick R Harris, proposed the tunnel jacking alternative.

Tunnel jacking has been used with significant success in Europe and Japan but this is by far the largest use of the technique in North America.

Fig 6. Ground freezing used to stabilise water-bearing material

The concrete boxes of each tunnel will be beneath the rail tracks and support the 278m face of each box jack cast within three large slurry-wall supported “To minimize friction between the concrete boxes and jacking pits and jacked into position some 8ft-30ft (2.5mthe frozen ground Interbeton’s patented John Ropkin 9m) beneath eight sets of rail tracks which must remain system of greased steel cables will be employed,” in service throughout. Three tunnels will be jacked into explained Stephen Taylor, Project Engineer for Hatch position, one for the I-93 access ramp and one each for Mott MacDonald. “Up to 1,000 ropes, anchored within the two I-90 carriageways. In cross section, the elements the thrust pit, create a carpet of 20mm cables across the are 38ft (11.5m) high x 80ft (24m) wide. The walls, floor top and under the bottom of the elements. and roof of the reinforced cast concrete elements are up to 7ft (2m) thick and each element ranges in length As the boxes are jack forward, the cables will payout from about 50ft (15m) to 150ft (45m) (Fig 6). There are close to the leading edge of the concrete boxes from two elements in the 150ft (45m) long access ramp and spools fixed to the inside ceiling and floor of the lead three each in the two I-90 underpasses of 250ft (76m) element.” Lubrication ducts cast into the concrete will and 350ft (106m) long. continually grease the cables to help reduce drag.

Contractor for this demanding job is the joint venture Friction on the side walls will be reduced using a between Slattery Skanska (New York)/Interbeton bentonite gel. To prevent the gel freezing in the frozen (The Netherlands)/J F White (Massachusetts)/Perini ground, heating elements have been cast into the tunnel Corp (Massachusetts). The JV’s bid of $397 million elements. Jacking will be a delicate balance between was the lowest when bids were opened in early 1997 keeping the ground frozen and the bentonite liquid. and Interbeton, with the most experience of tunnel Jacking forces will be transmitted from the base slab jacking, has contributed several alternatives to the into the post tensioned slurry diaphragm thrust wall of original design. each pit.

The material to be excavated is a mix of fill, peat and soft

By May 1999 freezing of the 150ft (45m) long I-93 access wet marine silts and clays which have very little cohesion. ramp had been established and jacking of this tunnel As part of at least $4 million of value engineering savings section is expected to take about six weeks during on the project, the JV suggested using ground freezing Summer 1999. to stabilize the soil rather than the original proposal for vertical and horizontal cement grouting, dewatering, and clay soil nailing. Freezewall, part of the Moretrench A comprehensive network of instrumentation has been Corporation of New Jersey (now part of the Keller Group), installed to monitor heave or settlement induced by the installed more than 1,600 vertical freeze pipes between operation. Train services into South Station cannot be the rail tracks and calcium chloride brine at -22°F will be interrupted and total heave allowance of the rail tracks circulated to accomplish the freeze. is a maximum 7in (175mm).

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To assist excavation of the 3,000ft2 (278m2) faces, the lead element of each tunnel is preceded by an 11ft (3.3m) long concrete shield with a steel fabricated cutting edge.

In a modern-day reincarnation of Brunel’s original mid1800s Thames Tunnel soft ground tunneling shield, the rectangular jacking shield is compartmentalized by an intermediate platform and vertical steel members. With one on the 50ft (15m) long intermediate platform and the other in the invert, the frozen core will be excavated by two high powered Webster roadheaders, cutting out the decommissioned freeze pipes as they are encountered.

At the same time, up to 90 x 891 ton-capacity jacks across the invert joint between the elements will push each box in the full element string forward at a rate of about 2ft to 9ft (0.5m-2.7m)/day.

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Once the first tunnel is jacked into position the second two will follow in succession. The last of the three jacks is scheduled to be complete by 2000.

Between the jacked tunnels and the immersed tube channel crossing, the underground alignment passes through a 100ft-200ft (30m-60m) section of cut-andcover. To work in the very soft wet material, the entire area is being treated with jet grouting and the Japanese soil mixing technique. Subcontract SMW/Seiko is using three enormous 5ft (1.5m) diameter triple auger units to mix cement grout into the soil. Detailed designer for the work is the Maguire/Harris JV and the contract’s main contractor Cashman/Kiewit/Perini/Atkinson JV will complete the subsequent cut-and-cover links. n

Ground freezing established to support insitu casting and casting and jacking of the tunnel elements with trains passing above and anti-drag cables for the top deck anchored to the jacking pit headwall and hanging from brackets inside the jacked element

Box jacking on a grand scale APRIL 1997

W

hen roads and railways cross on the same plane, one eventually has to give way. In Boston on the Central Artery/Tunnel (CA/T) Project, it is the new highway that has given way to the sets of rail tracks that have been serving Boston’s South Station railway terminus for more than 100 years. Engineers on the mega CA/T project have achieved the necessary gradient separation by going underneath and using a truly innovative solution.

Tunnel box jacking is not a new idea, nor that complex in concept, but on the scale used in Boston, that is new.

It took a visit to the site to appreciate the undertaking and realize how and why the project measures up to something special.

Other less expensive and less massive methods for achieving the same end result, including bored tunnel alternatives, were considered during the preliminary planning and design phases, but all things considered ground conditions, location, logistics - the selected tunnel jacking method is meeting the widest range of criteria in Boston. One of the most important of these has been to promote and maintain a high degree of confidence among third party owners through the planning, design, construction phases and during the lifetime of the facility. The principle third parties in this case are the Massachusetts Bay Transportation Authority (MBTA) that owns the railway facilities, and AMTRAK which maintains the tracks outside South Station on which pass several hundred trains daily.

Jacking alternative

The jacking concept is being applied in Boston to create three separate sections on the new subsurface I-90 highway as part of the overall $13.8 billion CA/T project.

Each jacked section carries two highway traffic lanes with an emergency breakdown lane, and each has an internal clearance of about 7m high x 20m wide. Two of the tunnel jacks take the eastbound and westbound carriageways of the I-90 highway under the rail tracks while the third is a two-lane I-90 westbound off ramp.

The tunnel jacking application in Boston is one of the largest uses of the technique in the world and one of the first applications of the method in the USA. The three tunnel sections comprise eight separate precast concrete elements of between 20m to 50m long, 11.5m high, and up to 24m wide, with heavily reinforced concrete floors and roof decks of 2m thick and walls of 1.8m thick.

The off-ramp tunnel is 51m long and comprises two precast jacked elements, while the two carriageway tunnels are 79m and 116m long and comprise three elements each.

Each element for the tunnel crossings is cast in large slurry wall supported jacking pits, a major construction undertaking in itself, and is being jacked into position some 2.5m to 12m beneath the rail tracks. At all times the tracks must remain in service. Any interruption to services would result in heavy penalties to the designers, contractors and highway project owners.

Project setup

In preliminary planning and design, the rail underpass was envisaged as a staged cut-and-cover operation moving each set of rail tracks one-by-one and building the highway beneath in short increments. The nondisruptive tunnel jacking alternative proposed by section designers Hatch Mott MacDonald was approved

by CA/T project designers Bechtel/Parsons Brinckerhoff, and it was on this proposal that contract documents were released.

In early 1997, the Slattery Skanska/Interbeton/J F White/ Perini Corp JV was awarded Contract C09A4 as the lowest of three bids at $398 million. “In addition to the jacked tunnels, the contract includes extensive cut-andcover tunnels, boat sections and elevated structures that comprise the huge I-90/I-93 highway interchange,” explained Gary Almeraris, Operations Manager for the JV. “This is the largest contract on the CA/T project, and all its construction activity must be managed and undertaken within the confines of a very restricted project site. The site is hemmed in on each side by the existing I-90 and I-93 highways, the Fort Point Channel, South Station and its railway tracks, as well as within close proximity to 11

Fig 7. Internal setup and principle of the tunnel jacking system

seven neighbouring CA/T construction contracts. It is a very challenging project.”

Construction program

After gaining access to the sites, the first task in was to excavate the three large casting and jacking pits adjacent to the rail tracks. These pits are 15m to 18m deep and are supported by slurry walls. A massive reinforced concrete slab of up to 1.5m thick provides a base to the pits and a suitable foundation on which to cast and then jack the elements of each tunnel section. A 6mm thick steel base plate provides the interface between the concrete of the base slab and the underside of the element to be moved. The back walls of the pits are designed to withstand thrust forces of 11,000-12,000 tonne needed to push each element forward and ultimate loads of 18,000-19,000 tonne.

Excavation of the pits gave the JV immediate experience of the geological conditions expected ahead of the tunnel jacking. Historical records and preliminary site investigation data in the contract documents had already predicted complex, mixed and unpredictable conditions. The rail tracks are built on reclaimed land under which are buried the granite blocks of the original sea front retaining wall and other timber pile-supported structures. The fill is primarily granular but contains various debris including chunks of concrete, steel, wood and abandoned rail track.

Below the fill are extensive continuous deposits of organic silt with fine sand and some peat. Underlying this, and comprising the thickest soil deposit at tunnel alignment, is marine clay with a section of softer clay beneath a deposit of stronger and less compressible clay at the top. The groundwater level is within 3m and 1.8m of the surface.

A major concern during design was stabilization of these weak soils.

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

Initially, the baseline design anticipated soil stabilization using chemical grouting and dewatering in the fill materials, horizontal jet grouting in the organic deposits, and soil nailing in the marine clay.

The JV, however, was concerned about the risks associated with 12

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

these methods and suggested ground freezing as a value engineering alternative.

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

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

Specialist sub-consultant Mueser Rutledge of New York designed the freeze program, and ground freezing subcontractor Freezewall was engaged to undertake the installation. More than 1,700 freeze pipes were

Outline of the jacked tunnels beneath the rail tracks

Expansion of these particular ground conditions when frozen is about 120mm on all sides, or about 1% to 2% by volume. Beneath the rail tracks a maximum heave of 175mm was specified.

“During the planning and design stage, many of the concerns put forward by the track owners and service operators (MBTA and AMTRAK) hinged on how the freeze has to be installed, what are the consequences of a freeze operation, and the presentation of an acceptable contingency plan, should one be needed to slow down the freeze,” explained Phil Rice, Resident Engineer on the contract for Bechtel/Parsons Brinckerhoff. “Together with MBTA and AMTRAK engineers and managers, in what has become a successful partnering relationship, these concerns were thoroughly investigated and managed to the acceptance of both the highway and the railway authorities.”

k boxes under the rail tracks will be cast and jacked

installed vertically and between the rail tracks. Calcium chloride (brine) at -30°C maintained the freeze. Being so close to Boston Harbor and the Fort Point Channel, the ground water is salty and -1°C is its freeze temperature.

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

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

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

Jacking program

Meanwhile, the two elements of the shortest of the three tunnels were cast at the same time in its jacking pit and these were ready to start jacking in October 1999.

Within the JV, a considerable degree of experience and technical know-how was contributed by Edmund Nuttall of the UK, a sister company of Interbeton within the HBG Group of the Netherlands. Edmund Nuttall has completed five tunnel jacking projects in the UK working in close co-operation with John Ropkins, a consulting engineer in the UK. The most recent of the five projects was the 50m long x 23m wide x 9.5m high culvert under the main railway near Maidenhead. This is believed to be the first

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

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From left: Obstacles and decommissioned freeze pipes were cut out as they were uncovered by the Webster Schaeff roadheaders used to excavate the frozen face in 12 cells in the shield of the leading element

tunnel jacking operation to include ground freezing for stabilization.

would be a difficult, time-consuming and uneconomical operation to retrieve the buried cables.

Through various agreements, Edmund Nuttall and John Ropkins are working to promote and execute tunnel box jacking world-wide through the HBG Group. Technical input at tender stage by Nuttall Ropkins to develop the freezing technique, the excavation methods and the open-face shield concept and design, in conjunction with box jacking experience, secured the contract for the JV and, through an ongoing commitment, has contributed to its success.

As well as preventing drag, the carpet of cables on the underside of the elements prevents the ground being compacted and produces the effect of tracks on which the box can slide. The cables across the top deck are designed in addition to transfer friction forces between the concrete roof surface and the greased cables to the cable anchors. The exact load on these upper cables is difficult to predict, but based on past experience and a conservative calculation, the load was estimated to be a maximum of 1.7 tonne/cable for the shorter ramp tunnel and 2.7 and 3.4 tonne/cable for the two longer I-90 carriageway tunnels.

A major contribution to the project was the innovative antidrag system (ADS) developed and patented by Ropkins.

Excavation sequence The concept is based on creating a carpet of closely To excavate the 278m2 face of the tunnels, the leading spaced, 19mm diameter steel cables across the top and element of each is preceded by a 3.3m long concrete bottom of the boxes to create a stationary separation shield which is fitted with a steel cutting edge and is layer between the moving box and the overlying and divided into 12 excavation cells by vertical walls and a underlying ground. These cables, about 1,000 across the temporary mezzanine working deck. top and another 1,000 across the bottom, are anchored using crimped-on copper sleeves to plates attached to The frozen ground is excavated for the most part by the thrust pit headwall bracing beams, and are paid out four high-powered purpose-designed Webster Schaeff from inside the element as the tunnel is jacked forward. roadheaders from the UK, two The free end lengths of the cables working on the invert and two on are stored on the inside of the The box jacks under the rail tracks the mezzanine. A Brokk hydraulic tunnel elements, on spools for the connect the roadways to the immersed jack hammer unit is available on bottom cables and in brackets in the tubes across the Fort Point Channel both levels to break up granite ceiling for the top sets. It is via slots boulders and harder obstacles. cast into the leading edges of the Excavated material falls from the shield at the front of each tunnel box mezzanine to the invert, where a that the cables are freely paid out as Gradall excavator and a CAT 906 the boxes move forward. Grease loader gather excavated material is fed continuously to the cables into a central muck pile. From through lubrication ducts cast into here a 42yd3 Wagner scoop tram the concrete, to prevent snagging transfers muck to a 4m3 skip at the and further reduce drag. back of the thrust pit which, when full, is lifted by crane for discharge Enough steel cable to see the on the surface (Fig 7). tunnel boxes to their final positions is needed in the cable reserves at “It is a machinery intensive the start of each jacking operation. operation,” said Steve Leius, Tunnel A total of more than 400km, or 1.5 Superintendent for the JV, “and the million feet, of steel cable is needed fleet also includes a man lift on each to complete the three tunnel lengths. deck and a 15 tonne cherry picker on Once the tunnels are in position, the the lower deck. With the machinery steel cable will be left in place. It 14

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

Jacking forces to push the tunnel boxes forward are applied only at the invert, with a main jacking station at the rear in the jacking pit, and an intermediate jacking station between the elements in each two- or threeelement string. The jacks used on the job have the same capacity of 485 tonne each at 42 MPa working pressure and 808 tonne each at the maximum allowable 70 MPa pressure. The thrust cylinders are 520mm diameter and have a maximum stroke of 1,067mm for the 25 jacks in the rear jacking station. The 28 to 32 jacks in the intermediate jacking stations have a 419mm stroke. All the jacks are grouped together by manifolds in clusters of two or four with one set of hydraulic hoses from the hydraulic pump to each cluster. Jacking forces of up to 15,000 tonne total are transmitted from the base slab into the post-tensioned slurry walls of each pit.

Each jacking station is activated in sequence, caterpillar style, pushing each element forward at a barely perceivable rate of about 30min/900mm stroke. After each 900mm stroke, spacers are inserted at the rear jacking station and are replaced with 3,600mm permanent spaces as the jacking progresses. The maximum 12,000 tonne pushing force available in the 25 jacks in the rear jacking station is sufficient to push the two or threeelement strings for about the first 50m without engaging the intermediate jacks. This helps maintain alignment, as do the guidewalls. The elements are cast within 1.2m high Nightime progress of the box jacking operation guidewalls cast into the jacking pits with foam filling of only about 25mm in the very tight tolerance gap between an expensive option but that in urban areas; under very the wall and the moving box. Friction on the side-walls shallow cover; beneath vital infrastructure which must can be reduced using a polymer gel lubricant. Heating be kept in operation throughout the construction period; elements cast into the concrete walls prevent the gel and through soft, non-homogeneous ground conditions freezing when in contact with the where dewatering is unacceptable frozen ground. Jacking is a delicate and settlement a major concern; the balance of keeping the ground A Brokk jack hammer breaks out harder method, in association with ground obstacles, top ADS cables disappear through frozen and the lubricant liquid. freezing for soil stabilization, is slots to the outside of the moving element the best method. After the Boston success, and supported by Progress successes elsewhere in the world, Having started in mid-October several similar projects were said 1999, the ramp tunnel jacking was to be on the drawing board for completed in December 1999. At other rail and road underpasses in the end of the process, survey the USA. measurements indicated that the leading edge of the two elements of the tunnel came to rest within 80mm At a presentation about the of their nominal vertical alignment, technique to the British Tunnelling and within 60mm from their nominal Society in January 2000, Doug horizontal location, well within the Allenby of Edmund Nuttall and John ±150mm tolerance specified. Tests Ropkins suggested that the future of the anti-drag system cables in could see jacks of longer boxes with the roof revealed that at the end of larger cross section areas; jacks for the 41m push, maximum load on a single radius curved tunnels; and single cable was 1 tonne, or 60% of jacks through a greater variety of the design value. ground conditions including rock.

It was agreed during the site visit that the tunnel jacking alternative is

At the June 2016 meeting of the BTS, Andrew Robinson, Christopher Howe and James Thomson of

15

Jacked Structure Ltd provided an update of recent developments in the jackedconcept for shallow tunnels and the March 2021 BTS meeting presented the details of a recent box jacking project in the UK.

Jacked tunnel boxes push through MAY 2001

B

y May 2001, all three jacked tunnels under the rail tracks were through. Tunnel jacking, in conjunction with ground freezing, was adopted as an alternative to the original concept of using jet grouting to stabilize the soft, saturated ground and building the highway tunnels beneath in a staged cut-and-cover operation, moving the tracks one-by-one.

Freezing was favored over jet grouting because the soft, wet soils of the area host several generations of bulkhead, bridge pier and building foundation structures and other ungraded fill debris and boulders.

These obstructions were expected to cause problems for both ground stabilization and tunnel excavation.

Ground freezing from the surface to near tunnel invert would stabilize the 11m high X 20m mining face without other means of support. It would also hold obstructions in place until excavated and without needing special handling.

The eight huge, heavily reinforced elements in the three tunnel sections of 51m, 79m and 116m long and 11.5m high and up to 24m wide accommodate two traffic lanes each and an emergency breakdown lane.

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

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

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

Forces of up to 15,000 tonne were applied to push the sting of elements in each tunnel section forward at a barely perceptible rate of about 30 minutes/900mm stroke. Each jacked tunnel came to rest well within the ± 150mm vertical and horizontal tolerances specified and operation of the rail tracks above continued undisrupted throughout. n

Frozen ground provided stabilization and support for successful hole through of the last and longest jacked tunnel box.

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

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Clockwise from left: Northbound I-93 inauguration celebrations; Night work along Atlantic Avenue; Widest point on the underground highway at a six lane exit ramp; Entrance to the northbound I-93 tunnel near Kneeland Street

Big Dig begins opening MAY 2003

T

he long road towards transformation of downtown Boston has finally begun. At the end of March 2003, politicians and dignitaries joined project managers and workers and the public to celebrate the opening of the new I-93 northbound lanes of the Big Dig Central Artery/Tunnel Project. Built to stream traffic up to 100ft (30m) beneath the city, the project will allow the old, dangerously overloaded and deteriorating elevated viaduct highway to be taken down.

Started back in May 1991, construction of the project has demanded the dedication and determination of a legion of consultants, contractors and tunnel excavation workers.

With a total length of 7.5 miles (12km) through and around the downtown area of Boston, the project comprises more than 161 traffic lane miles (260 traffic lane km), the world’s largest tunnel ventilation system, four major interchanges, a new bridge over the Charles River, and more than 46km of utility relocation.

In January 2003, the I-90 part of the project opened to link traffic from the enormous I-90/I-93 interchange to the Ted Williams immersed tube tunnel and on to Boston’s north shore and Logan Airport. This underground section of the project includes three innovative box tunnels, jacked into position just feet beneath live rail tracks at the approach to Boston’s main South Station, and the concrete immersed

tube continuation across Fort Point Channel. Constructed at a cost of $6.5 billion, this 3.5 mile section of the project is the most costly stretch of highway/mile in the world.

The jacked tunnels - designed by subconsultant Hatch Mott MacDonald and constructed by the Slattery Skanska/ Interbeton/JFWhite/Perini JV - started as enormous cast concrete elements of 35ft high x 75ft wide (11.5m x 24m) and up to 150ft (45m) long, and were jacked into position as the rectangular tunnel face was excavated using small roadheaders through soft water-bearing soils stabilized by ground freezing. Among the many awards likely to be received for the Big Dig efforts, the jacked tunnels have already earned a British Construction Industry International Award and the 2003 Charles Pankow Award for Innovation.

With traffic now using the tunnels of the northbound I-93 carriageway, cut-and-cover construction of the southbound carriageway continues towards an anticipated opening date in early 2004. Following that, work will begin on dismantling the old elevated structure that has divided the city for more than 50 years.

The greatest detraction to the tremendous work achieved for this extraordinary project is the constant reminder that the cost has increased from an estimated $6 billion in 1991 to an official figure today of $15 billion. This has caused considerable concern among State, City and 17

some 16 million yd3 of material from beneath one of the oldest cities in the USA. Mathew Amorello, Chairman of the Massachusetts Turnpike Authority (MIA) said: “The project rivals anything in history built by man. It is an incredible achievement.”

The last piece of the viaduct comes down

Federal funding agencies and several investigations into the possible causes have been initiated.

Despite this, residents and visitors are becoming acquainted with the city’s new underground highway infrastructure.

Big Dig finally done

It was in March 2004, five years late and billions over budget, that digging for the Big Dig project was finally done. The last segment of the 7.5 miles of underground highway opened to traffic in December 2003 marking the end of major construction on one of the largest, and most expensive engineering projects in human history.

At peak, more than 5,000 construction workers were employed on the Big Dig and excavation work removed

The achievement is rivaled only by its staggering cost.

Since its inception in 1987 the cost estimates for the project ballooned from $4 billion (in 2004-dollar value) to $14.6 billion. Revelations over hidden cost overruns remain a contentious issue and the Massachusetts Turnpike Authority is planning a $150 million lawsuit against the Bechtel/Parsons Brinckerhoff team that managed the project.

With traffic finally redirected into the underground alignment, the elevated highway, nicknamed the Green Monster, is now coming down one piece at a time. Testa of Lynnfield, Massachusetts is the subcontractor handling the delicate deconstruction. Prior to being dismantled, the 1 mile long structure must be painted to keep lead in earlier coats of paint from becoming airborne. It must also be constantly hosed down to minimize dust.

The estimated $62 million cost of the demolition is included in the overall Big Dig budget. Doug Hanchett with MTA explained that “demolition started in December 2003 and is on schedule to be complete by August 2004.”

Large urban parks are to emerge on land where the giant green steel skeleton of the Central Artery once stood. n

Photo credit Greenway Conservancy

Boston city center as it is today with the Rose Fitzgerald Kennedy Greenway outlining the route of where once stood the elevated highway and with traffic now passing unrestricted through the cut-and-cover carriageways beneath

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Big Dig lessons learned MAY 2003

I

n 2003, at the ITA WTC (International Tunnelling and Underground Space Association World Tunnel Congress) Frederick P. Salvucci of the Department of Civil & Environmental Engineering at MIT, Cambridge; Transportation Advisor to Boston Mayor Kevin White (1970-1974); and Secretary of Transportation for the Commonwealth of Massachusetts under Governor Michael Dukakis (1975-1978), gave a keynote address focusing on the Big Dig project in Boston and the lessons to be learned that it revealed.

At the time, the Central Artery/Tunnel Big Dig infrastructure project was approaching the end of construction, various parts of the underground transportation network were beginning to become available to the public, and within three years the elevated highway that it is designed to replace will start coming down to make way for surface parks and air rights development. But as the benefits of the largest highway construction project in the USA to date are about to become visible and real, the cost of the project has escalated from a $6 billion estimate as construction was about to begin in 1990 to a current estimate of $15 billion and still rising. Among the lessons that can be learned from this project Salvucci cited the following in his keynote address.

would have been 90% Federally funded as part of the Interstate highway system; and the region would have been enjoying the benefits of the completed project for more than five years by now.”

The delayed start of construction to beyond 1991 not only delayed project benefits and drove costs up because of inflation, it also shifted the project out of the Federal Interstate highway funding process. Under the process the Federal Government paid 90% of actual project final cost of Interstate highway projects and shielded States from much cost increase risk. The post-1991 Federal funding system forced Massachusetts to bear most of the exposure on cost increases beyond the 1991 $6 billion estimate.

Further delays in the 1990s, caused by the decision to reconsider design in the Charles River vicinity, at the South Bay interchange, and at Logan Airport, compounded the problem of cost growth, postponed major project benefits, and may eliminate some project benefits. These changes were not subjected to the public accountability process previously provided by the biennial Interstate Cost Estimate audit of the Federal Government. This was eliminated under the 1991 ISTEA legislation.

Salvucci went on to say that at the local level, the extremist privatization philosophy of Governor Weld’s administration (1991–1997) dismantled much of the public In opening his address, Salvucci explained the enormous sector structure for managing the engineering and benefits to the economy and quality of life in Boston project construction, leaving the private sector Bechtel/ obtained as a result of the project.

Parsons Brinckerhoff JV designers Designed to complement the and construction managers as the modernization of the city’s public Delay is the most significant only source of institutional memory. transit and commuter rail systems, driver of cost increases and support policies to limit parking to The Laszard Freres Report of 1990, reduced project benefit within street capacity, and encourage conducted with intense participation increased use of public transportation, of the business community, the Big Dig will essentially double highway capacity recommended that the Big Dig facilities be placed in a east-west across Boston Harbor and north-south through new metropolitan highway agency and financed with toll the downtown area avoiding previously threatened revenue to ensure their proper operation and maintenance. gridlock in the city center. The construction process itself Deferred implementation of this recommendation for six has provided major impetus to the regional economy, with years, left the Bechtel/PB team in the difficult position of a net inflow of $5 billion during the decade of the 1990s. constructing the largest public works project in the country without the participation of the eventual owner. Moreover, Only by understanding the significant benefits of the project reduced public management capacity undermined the and sheer necessity of it to the regional economy is it State’s ability to manage conflict between the Bechtel/PB possible to understand how, in the usually fractious political construction management and final design consultants, environment of Boston, broad bipartisan political, business, or to make informed judgments on value engineering labor, and community support has continued despite serious opportunities proposed by third parties. cost increases, borne mostly by the City and State.

The four-year delay caused by reconsidering the One reason the project has maintained public support is Charles River crossing, combined with the dismantling that the State Government has resisted the temptation to of public sector capacity to manage interfaces and value shift the burden of cost increases to the general citizenry engineering opportunities, and the high cost of real estate and private sector. acquisition, are the basic building blocks that caused the 1990 $6 billion estimate to rise to the current $15 billion estimate. In addition, while increasing project value, “No one, to my knowledge,” said Salvucci, “has ever acceptance of legitimate scope additions, particularly suggested that environmental concerns motivated the from FHWA, such as intelligent transportation systems delay imposed on the project by the Federal Highway capacity, also added cost.

Administration (FHWA) during the Reagan Administration, but this cost the project dearly. If the “final” EnvironAs the costs mounted, the Weld administration hid mental Impact Statement (EIS) of 1983 had not been held the increases by shifting anticipated toll revenue from hostage by the Reagan Administration for seven years, operation and maintenance to servicing debt, and by the cost would have been below $6 billion; the project 19

shifting costs to the future through the issue of bonds and revenue anticipation notes. These ‘creative financing’ policies left the project with no operation and maintenance plan and were adopted without honest disclosure of problems that would have been required by the sinceabolished FHWA biennial audit. With no honest disclosure to stimulate timely search for solutions, problems were hidden for as long as possible and to the point where no options were available.

Compared experience

and skill of the public and private sector engineers and construction managers who have been building the Big Dig, are a credit to the profession. It is easy to take potshots at Big Dig cost increases, said Salvucci, but maintaining an extremely high safety standard and solving hundreds of near-impossible challenges while conducting the equivalent of open-heart surgery on the city’s center should be respected and celebrated.

The major challenge now is prudent operation and maintenance of these expensive investments

During the same time period, the Boston Harbor Cleanup Project, estimated in 1990 to cost a similar $6 billion magnitude as the Big Dig, was completed on schedule and within budget. This was achieved by competent public managers using the private consultant Kaiser for basic design and construction management. As a major difference, the Harbor Cleanup was mandated by court order. As such, the public sector management and public accountability functions were protected by Judge Mazzone. Scope changes did occur in the project, but these were incorporated within the context of public and court scrutiny and offset under a public sector management capacity of ‘institutional memory’.

If the major interstate highways absorb traffic away from city streets to enhance the pedestrian friendly quality of public spaces, and if high-density pedestrian and transitoriented development expands the economy of the city, without increasing congestion and environmental impacts, then the Big Dig will be a success. On the other hand, if inadequate maintenance erodes the value of both highway facilities and parks and if large additional amounts of parking undermine the transit and pedestrian orientation of the city, the project will have failed.

At the same time, while the policy management of the Big Dig suffered under the extreme privatization theories of the Weld administration, the dedication, creativity

First and foremost, said Salvucci, I believe that, with all of its implementation problems, the Big Dig will deliver enormous benefits to the Boston metropolitan area in

Public demand for Big Dig accountability SEPTEMBER 2006

P

olitical posturing, far-reaching investigations, and public mistrust began to cast long shadows over Boston’s Big Dig project when in July 2006, panels of the tunnel’s suspended ventilation duct ceiling fell onto moving vehicle, killing 39-year-old passenger. The car was traveling on the I-90 approach to the Ted Williams immersed tube tunnel across Boston Harbor towards Logan Airport and was within a few hundred feet of leaving the tunnel into a short open cut boat section ahead of the Ted Williams portal. The driver crawled from the wreckage. The I-90 underground highways were closed immediately and indefinitely while the accident was investigated.

The fatality initiated the most far-reaching probe of the project to date. State and Federal inquiries, including an investigation that could lead to charges of negligent homicide, have resulted in subpoenas being issued to several companies including the project design, construction and program management JV of Bechtel and Parsons Brinckerhoff, as well as detailed designer of the tunnel involved, Gannett Fleming, and its contractor, Modern Continental.

Political fallout includes resignation in August of Matthew Amorello, Chairman of former Project Operator, the Massachusetts Turnpike Authority (MTA), and appointment, through emergency legislation, of the Governor’s office as controller of the quasi-independent MTA - something that Governor Mitt Romney has been seeking since he came to office three years ago. There is also political haggling over individuals selected as leaders of different investigations amid charges of alleged conflicts of interest.

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Initial findings into the cause of the fatal incident revealed that epoxy-resin anchored bolts holding tie rods and flanges that support the precast panels of the suspended ceiling had failed causing four 4m wide x 2m long x 150mm thick, 3 ton reinforced concrete panels to fall. Subsequent examination revealed that several more bolts in the I-90 tunnels were suspect or close to failing.

Epoxy anchored bolts were used as part of the suspended ceiling design in the I-90 Big Dig cut-and- cover tunnels and in the Ted Williams immersed tube tunnel. Heavier precast concrete ceiling panels were adopted for the Big Dig tunnels as a value engineering change from lightweight panels used in the Ted Williams link.

“The Ted Williams tunnel panels are about one third the weight of the I-90/I-93 ceiling panels,’’ said Jonathon Carlisle, Press Secretary of the Massachusetts Executive Office of Transportation. He said “the bolts for the ceiling hangers in the I-90 tunnels are bigger ard deeper than in the Ted Williams Tunnel” but that, because the Massachusetts Department of Transportation had only recently taken over responsibility for the highway system from the MTA, “we are not clear on the history of the project. When more suspect bolts were found in the I-90 tunnels than in the Ted Williams Tunnel, the concern was for a systemic problem in the I-90 tunnels.

A different system of steel-to-steel fixing was used for the Big Dig I-93 tunnels with the steel receivers embedded in the casting of the concrete top deck of the cut-and-cover alignment.

Rising costs for installing the ceiling-panel system in the Ted Williams Tunnel were blamed in an inspection

terms of laying the groundwork for smart, environmentally sustainable growth. In metropolitan areas throughout the USA, similar re-conceptualization of aging infrastructure is needed. These are expensive and potentially disruptive processes, and it is in the national interest to encourage this process in a timely, thorough, and thoughtful manner.

Federal encouragement means stable, dedicated funding backed by responsible, competent oversight of the use of those funds. It requires developing a shared vision of the national importance of the renewal and redevelopment of major infrastructure systems and development of public sector competency in overseeing implementation of these projects in an environmentally responsible way.

This constitutes an institution-building effort on the scale of the Interstate Highway Program initiated in 1956 by President Eisenhower.

In its time, the Big Dig will be viewed as either the last Interstate project or the first interstate project to comply fully with the spirit of the 1969 National Environmental

Vehicle crushed by fallen ceiling panels causing death of a passenger

report on “poor design specifications, inadequate management of the construction, improper load testing, and unauthorized deviations from specification”. The report found that bolts drilled into heavily reinforced concrete were being cut short to avoid rebar and that resin bonds had failed pull tests.

The Ted Williams Tunnel was built earlier than the Big Dig cut- and-cover tunnels and opened in 1995/96. The mostly cut-and-cover Big Dig tunnels of the I-90 and the I-93 to replace the old elevated Central Artery highway underground were completed in December 2004.

The Big Dig took 15 years to complete, twice as long as originally stated, and has cost $14.6 billion, more than double the 1990 $6 billion start-of-construction estimate and five times the near $3 billion original environmental impact statement estimate of 1983.

Legal, moral and ethical issues of Big Dig troubles

The fatal accident on 10 July, 2006 is the most tragic and damning of a catalogue of design, construction, management, funding and political problems that have dogged the Big Dig for 20 plus years.

Policy Act and lead the transition process towards ongoing and continual infrastructure redevelopment programs.

Finally, the Big Dig would not have been possible without the national funding which provided the financial stability to make such a large infrastructure renewal project feasible. Equally fundamental was the local planning and environmental processes which allowed the development of a strong enough public consensus to see the project through to completion. Unforeseen circumstances, changes in government administrations often accompanied by major shifts in political philosophy - as well as changes in the economic context, will always occur during implementation of such large projects. In my judgement the most fundamental asset the Boston region has had through the last three-and-a-half decades is a thoughtful process to develop an adequate level of consensus on transit and highway investments rooted in a broad, environmentally based sense of direction for the region as a whole. The most fundamental liability the project has had is that after an enormous amount of prior environmental analysis and full public disclosure, major changes were made during construction with little analysis of the environmental impact or the cost consequences.

In my view, strengthening the environmental compliance oversight and full disclosure of issues in real time is of major importance for strengthening the credibility of our ability to undertake large projects well. n

For Frederick Salvucci, Commonwealth Secretary of Transportation for the Democrat Administrations of Governor Michael Dukakis that approved the project in the late 1970s/early 1980s, “there is a clear line of accountability to Bechtel/Parsons Brinckerhoff”. In a telephone interview, Salvucci said that the B/PB JV was appointed “by our Administration in 1986” on a cost-plus type of renewable contract “to be the entity of seamless accountability of the job, from preliminary design and oversight of final design to management of project program and construction supervision to project opening.”

He said, “we also believed that the project needed a belts and braces system of governance and a strong public agency to manage the managers [B/PB]. As we approached the construction phase, it was clear that this could not be carried out by the Massachusetts Department of Transportation. We recommended in 1990 that either the Port Authority or the Massachusetts Turnpike Authority, or a combination of both, take over this role.”

He said that while the incoming Administration of Republican Governor William Weld in 1991 agreed with the recommendation, the decision to do so was deferred for six years “leaving Bechtel/Parsons Brinkerhoff in the difficult position of constructing the largest public works project in the country without the participation of the eventual owner [and] as the only source of institutional memory.”

In the 2003, Salvucci cited the “extremist privatization philosophy” of the Weld Administration for “dismantling much of the public sector structure of managing the project and [thereby] undermined the State’s ability to manage conflict between Bechtel/PB and the final design consultants or to make informed judgements on value engineering opportunities proposed by third parties.” (see p19). “But this is no excuse,” he said. “It is in fact cause for greater diligence.”

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Inspections after the fatal accident revealed many failing anchor bolts of the suspended transverse ventilation ceiling panels

Bechtel declined to contribute to this report and Parsons Brinckerhoff said that Bechtel is handling all media enquiries for the JV. Instead of agreeing to an interview Bechtel, directed the media to its website where a statement about the tragic death reads “B/PB immediately offered its support” but that “once the accident came under criminal investigation, State authorities limited access to the accident site and project records.” It concluded: “We firmly believe the project’s processes for engineering, construction, and quality assurance were appropriate and robust.”

A spokesman for the Turnpike Authority said that B/PB’s management of the project ended in January 2006 with substantial completion of the work, and that the MTA took over remaining finishing works. These works, according to the MTA’s traffic management website, require frequent system lane closures. A newspaper report quoted a Bechtel spokesman saying that the JV earned $130 million for its involvement on the project and that its liability for project losses is limited to $150 million. This may be lifted depending on current investigation findings.

A different report states that in 1997 an “integrated project management” team of B/PB, MTA and Department of Transportation personnel was imposed on the project which might have blurred the line of accountability.

Under separate legal action, State Attorney General Tom Reilly continues his demand that B/PB pay back some $108 million in fees to compensate for a list of more than 200 claims of “shoddy work”. These include causes of an incident in September 2004 when volumes of water gushed into a section of the tunnels closing them to traffic as this and other identified leaks were repaired. Closure of lanes backed-up traffic through the underground highway.

Newspaper reports claim that the project’s 500,000-gallon capacity drainage system handled 26 million gallons of water between December and September and that there are some 400 leaks identified in the underground structures. Bechtel/Parsons Brinckerhoff, construction managers of the massive project, have released a statement explaining that leaks were expected, and that civil works are still being finalized. Governor Romney is said to have called for the boss of the Turnpike Authority, the project’s owner, to resign. Negotiations to settle this action were interrupted by the fatal ceiling panel accident.

In another pending action, six managers of a concrete company were indicted in May 2006 on charges of supplying substandard concrete to the project. In addition, the victim’s family of July’s fatal accident has also signaled its intent to sue companies and Government agencies involved.

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As these political and legal issues play out, Salvucci, a civil engineer and senior lecturer with the Center for Transportation and Logistics at MIT (the Massachusetts Institute of Technology), said: “As well as the legal implications, there are moral and ethical issues here.

Bechtel/PB have failed in their duty to undertake their role properly. How can the public now have confidence in an engineering profession when we can’t account for adequate ceiling bolts. This is a horror show.’’ More significantly, he said, “after the issue of the leaks and now this, what else might be wrong?” He hoped that the review of the highway system initiated by Governor Romney, will be “a real soup to nuts” review of the entire project and that this will be the foundation of a long-term proactive inspection and maintenance regime.

“This infrastructure is going to cost much more than anticipated to operate” he said. “The authorities will not like to hear that. The tradition is to hide items of large expenditure from the taxpayers and to repair public infrastructure only as needed, but that will not do in this case. The risk of major incidents happening again is too high. The financial consequences are already substantial. Toll revenue has been lost during closure of the system and more money is now being spent on ceiling repairs. It would have cost comparatively little to correct construction quality issues at the time compared to these consequential costs.”

While Boston comes to grips with the aftermath of the accident, there have been ramifications on other publicly funded megaprojects in the nation including the Alaskan Way project in Seattle, which proposes a similar large scale construction operation to replace the elevated highway underground in cut-and-cover tunnels. Such projects can expect greater scrutiny by funding agencies and political activists with the intention of eliminating whatever lapses in management control resulted in the Big Dig faults and their dire consequences.

Big Dig charges DECEMBER 2006

Fifteen companies involved on the Bid Dig in Boston were hit in late November 2006 with a criminal lawsuit filed by the Commonwealth of Massachusetts.

State Attorney General Thomas Reilly said the investigation by his office convinced him that people and companies connected to the project should face manslaughter charges after the ceiling panel collapse in the I-90 connector tunnel in July killed a car passenger.

became known that B/PB was being allowed to supervise ceiling repairs even as their work was under investigation.

Romney said his Transportation Secretary had “made a mistake” and promptly ordered all B/PB workers off the project. The JV’s services are still needed to complete other parts of the $14.6 billion Big Dig project.

Big Dig indictment SEPTEMBER 2007

The supplier of the epoxy bolt fixing compound blamed for the fatal Big Dig Tunnel ceiling collapse, has been charged with one count of involuntary manslaughter.

Action against Powers Fasteners Inc is the first criminal indictment following the July 2006 accident.

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fter the accident on in July, the I-90 tunnel connecting the I-93 and the Ted Williams Tunnel remained closed in both directions with no forecast for when it might reopen. The I-93 tunnels were not closed although the alternative fixing system of their ceiling panels was also under inspection. The Ted Williams Tunnel eastbound was closed as a result of the I-90 being closed and westbound traffic was slowed by inspection lane closures. Various contractors working on retainers carried out inspection and repair works in the I-90 connector tunnels. By late August, tests of bolts in the eastbound tunnel were complete, tests were progressing in the westbound tunnel, and design of works to reinforce the ceiling panel system in the I-90 tunnels was on-going.

The I-90 underground highway normally carries some 200,000 vehicles/day.

The charges stem from a July 2007 report by the National Transportation Safety Board (NTSB) blaming the use of fast-set instead of standard-set epoxy for the failed bonding of bolts that anchor the suspended ceiling in the tunnel. The NTSB said Powers Fasteners provided “inadequate and misleading information” about the potentially deadly consequences of using fast setting epoxy to secure the ceiling bolts. In a terse statement, Jeffrey Powers, the company’s president said they were “stunned, beyond belief” at the indictment adding that the company had filled an order for standard set epoxy and was unaware that the fast-set had been used instead.

The Board’s report made no mention of an earlier investigation charging that anchor bolts had been cut to fit holes drilled shorter to avoid rebar in the heavily reinforced concrete of the underground structure.

The NTSB report also blamed ceiling designer Gannett Fleming for failing to specify the appropriate epoxy, and tunnel contractor Modern Continental, and project construction managers Bechtel/Parson Brinckerhoff for failing to determine that the wrong material was being used when bolts showed evidence of coming loose during construction. The Massachusetts Turnpike Authority (MTA), the owner of the underground highway, was faulted for not instituting a timely tunnel inspection program that would have revealed the problem.

The lawsuit states that project and construction managers, the Bechtel/Parsons Brinckerhoff (B/PB) JV, were “grossly negligent” while the others, including section contractor Modern Continental, with section designers, consultants and insurance companies were “negligent”.

Massachusetts continues its investigation, and more indictments could follow. The victim’s family has also filed a wrongful-death lawsuit. n

The filing came two days after traffic finally started flowing again on a key mile long ramp connecting the Ted Williams Tunnel to the I-93. It was closed when the fatality in July sparked a full scale, system-wide inspection and repair of suspect tunnel ceiling fixtures. Reilly said project managers knew there were problems with the ceiling panels fixtures and with the training of some workers, yet they pressed ahead, not double-checking the work.

Lawyers say the State will have a tough time proving gross negligence. It will have to supply evidence that project engineers knew their design or actions would likely result in personal injury or property damage and were willing to accept the risk. Bechtel’s liability cap prevents it from being sued for more than $150 million unless it is found to be guilty of gross negligence.

maintenance, and design and construction quality issues have come to light, some of which have contributed to fatalities in traffic accident situations and many that have increased the cost of maintaining and operating the network of underground highway infrastructure. As the RETC conference of the USA prepares to convene its 2023 event in Boston, it will be interesting to catch up on the industry’s take on where appreciation of the project - politically, technologically, legally - stands currently. One thing is for certain, the daily activity of the city is completely transformed from where it was at the end of the 1990s, due fundamentally to the completion of the Big Dig scope of underground engineering and construction. For certain also, if undertaken today, different excavation methods would be adopted and applied.

Meanwhile, an embarrassed Governor Mitt Romney (2003–2007) had to back pedal in October when it

Footnote: As the years have gone on other safety,

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Highway. gravels shaft mile sewag dloose the deep alluvial the mom being new under element and site mobilizat oston, theestab hwest of the a 200ft ofNort ’s first LRT O proje At the to accept the 4ukee, shares As the region After primary . From dedicate ess forMilwa tts,lishe Boston ion, but from Hensel-Ph ent with groun 1952.

Mass the anticipated othe ct in we succ has are chuse build the 1968. nd ority, will d each the e tunnel d Ana in are to r boulders street ation Seattl and mining by the shoreline, Quincy rpor Island Massa been treatmen end, begin. auth olarge just beyochargedfrom outlets inthe looking TBM to for buses e’s the Chicag answe is the criticthe Island contract and futur At the the seco is sinking the d Transitalong at Deer the rged through short for was withit has cities by inco remain doning 1 mile back only Formation 60-70ft ess tly built toplan Parallel 1.3 TBMrs to WRC site, t plant for about network, Diego set ront rounurban al Sanifican was een procwaterf thesign Discharge s Area Rapirated LRT y (EPA) traffic on (18d-the-cloc week plant “Ideall schedule betw an uphi nd WCSO TBMClayton acce mile , thethrough pass under the Agenclace largeg US 21m) to , tion belowisofdischa y,/day an long maximum.

(2km) rge with a closed 230ft frustratin the waste designed those T, the Dalla ss shaft Obayashi/ encedand integ among stion.. We will ll gradient k onconge about in been ing,1986 a fulllong discha street Protec will exca influ , pressu allems the expectation tunne At Cityp seabed isionone mile the ions s of be better For DAR manage an g prob day for the d bybelow and often nment ls, three to 50% of week theends rized tunnel ent is operate prov to the s. otiatscreen than up to8hr dulin vate 23,0 from which ing afternoon in the ption shaft centra Enviro to 158ft in the rece to have main upcause lopm shifts/day, more courseNeg 45ft leadthe aton harbor. the buses l distric water bearin ing215ft littlethe tenance federa expensive et . Part deveits water and lscheabout is a main 00ft (7km ages of ed in 1983 Station thes,polluti issue shield Shaf 2).on. theT agre (65m day inay. stati The first present 4 1 and offtena In the waste out of the 6 days ,” said John t will adva would e into (FigsLRT g .ground thence on ) deep Jim once a essw Budg somet arduous, thet, will take design ve hing und pass streetof sea level mile/h place TBMof ded. d sewag dissol and rgro North Aven) in of anand rs tech takes a long, at this point. r comm Atkinson, / rding to MacDonald, nce 20,5south , laun and DAR to its 148ft will carry eme upeach mach conts and agre mile/hr in unde increa nician uter tide Pionee accotreate sive and that this is ill-foun chedr at the Expr ciently planning e with Herr ine on“but there DART: to dilute lope 00ft ofebbing traffic ract Projec comprehen helme on each peak with ue with onesentthe lace athe ond.with rand insuffi (45m) deep ys, but of proves period t Manag (6.2k er flows overw the side to arriv with complex that many are deep Citypes dela ent forl abilityatsincedeve enknsky mach been s. to about und statin studies full-ti12 Herr r’s natura beach nce investigatio er of eithe Parsons echtscrapers infor sitergro tie backs Clear Cree m) me Herr an uphi Rockdale on the designer Intensive n light long and time The , own Managem n on better unde excavatedenknecht. We ine. We also have has convenie together rs, onethe Waste anchoring by project with ion harbo gree “Twoalong pany enkn Tunneling these ically k rece prepared m TBMs the high costof Constructwaste can be echtwe need reporttowe finishbased the solutio To date, in theption ll gradient biolog will pay the LRT and they n ofas7-11 a majori both began in as far to prick ural CDM are atunnel er systegeological hland Com to re that, . easy access caused shaft. the WCS itectof ms, r cont a fixed cutte minim route and to deal indicate Atkinson/Dil nal chai thethe November will tyract arch been given of the start dateual the Sout Science proble and of the tunnel Director g group .” Engineerin ilation effluent outfall ed outfalls natiothrough n, O tunn to theum or pressu ities cost/yd Asse ng reaches requAlso, 1986 supp vent lingha ly all the rdfour 3 inter face. retur author Martin, excited to have construction chose istance Knowi mbly by when pass irem els and m is individ 1996 towa the tunnel will s lowes in of an JV d the public com e long-d lie two dry, ent the tunnel sea of as ofwon cutte rock open-faced consent compe the t of eight the work said to and the first dule Guy oving pare nt case, cont plete to get exca an avid ribut 1 and it takes are under 3 ent theTBM 14 long predicted, F r need y to get byOften r civil “We are contra compe hold treatm and machinesdecree tentdground the sche s.” the upper said othe below the are about t currently ct with vation of Bostons,’s of large, slow-m wouldforReaches geology.

Ken at Rock are read only inn. which there water . In millio with breast facili different h, with deadline the, we the Johnston part material $61.6 million ting bids at $44.2 the larges theaction quite 1980s, dale Shaf store sible operation conscience into last and t $40 whicand the WCSof are taking on the more plates sandy d y respon of to ty in operation abou , the City’ing ingravelly be ide, ated lia. worldw O the and into contface ionmust softer ationcost scale tunnels much sea usual 30-to- Engineer’s Estima million, well t, theOf the stati porous in agenc ract.in“As of the gripp wet s Proje 7 Nove operat ofgranular Found force ingthem rolling anaestim mber 2007 y, Austra in pressure theervariou runn a the State a job of this te. Instea ents, will 36 y on. ions.” secti in hydrostatic well as condit in Thefull rvation on sued beSydne barLaw irem to was 7requ jogger Agencare lace d of ,” me.Conse and its beach ved ent and the scale, Seattlemonth construction nd secti , going edown anticipated the TBM ct Manager for Citypuction constr was “techn sonmachin s. The Protection proposals, tight 17 month all treatm 2 and 4Act me, station mnmentalReaches the sche period now invol undercing costs Metro, the drives, undergrou ically forservice syste the one from sewer Water s plan has with flow from expected. silty material nal sche andosals program Cityplace nd sections prop only the cont the client, impos for is also Seattle superior andwith starterl Enviro redu origi permeable by early n competent l 7-mile CBD ,with inches Robbins , less m)Federa CDM facilitie ated Federal Clean to have the r r the ract the ntow in a (32k 1972 ed sued -based makin most econo 1990.

A Federa Deer Island to spar ged the on more dowthe Unde turnmile an elevon ay Boston undergrou on of earlie 20 mical.”

In char n part of by e (right) t reliable machi To meet this, the system in servic a the State. in the ing g delivery Robbin to Deer Island dary pressure. not )enforc the (EPA) for(11km T was taking place s moderate by suing at abou rge on Atkinson easy and e more an order the harbor $218 millio nes, one down versi osal for ed, whe n DARrity rundischa d Expressw atedded this secti The machin y and secon and delive quick. respon t 7 miles neede esse ever for each prop was1986 impos EPAestim 3, thereunder es are quite 1989rces meMay andcarried red quickl 1depr tube, design d two Island ns how . After primar 8-10 miles out to InResou was to of ian and thewas original rground for abou reaches schein of the nAutho Nut open-faced y. finding and conditions long tunnel estio (CBD) andt expe nsive The the ed, built sugg)estio Court med gravelly Water d.tts ent be e excavation shields. To different from the discharged of water where (7.6km porous, rectify or the district the a sugg foun Distric e artm In to an ran unde mile Thes plenum, will chuse 5 m t the ess more be TBM Dep abov the provide optimu The geolog backhoe such to 110ft progra familia busin In using a no ture into the median. way the effluen man had Massa freezing. ent paddle-type ent, ade can y be High strucentry es the central n. Approval for which m face access r limits in about can naturally dilute of ground on implem treatm tripod of clay with the is mostly over-consolid excavator n. thee assistance a alternativ ) tanti hadallytoat-gr the harbor inter-reacting the State ocean without , to drequire 1999. millio by or at grad water table is mounted .7than (MWRA t.beyon $1.1 billio chamber, subs of the ated sands, expected is e sea cheaper built ted 1). hydrau later men entry 14 $828 of runs 47 two (Fig man no balanc Pionee to lines and at rising rejec safe on a other machin lic cylinde d 4, silt and n by ruling LRT ing waste close to 2 and r Square Station the align face. ical were theecolog situatio denied now being built and reaches Theremain is price rs. Robbin Washington es to this the court alon e water table airgto help hed.the d by holdthe s has (Fig 1). North the surface south of the rade Ther design, one will reac compresse DC Metro complyofwith is residents -of-ways biodeg todegree scheme r side Coordinated andwas of the Station Caracas Metro worknd. in 1974 and used on the ay Deer Island facility s/ over conso well below the tunnel thergrou rail right s eithe Expresswsed promise unde time to lose. newly ,formed , the the other scale busin be of noess lidated materi in 1978. gallon existing elevation The to ral left used on the n, the 1989 a comts dated in boxeparteted, has centne of thethe propo and the dry als can be 1,200 million thedeadli ion cost esswaydivisioIn 37 June a short nsultan system such compl consity mmo truct very hard.

From Exprement sub-co of more than integral The 21ft (6.4m) its ld manag mral be acco) and lace the g anWhen native.own progra atedcapac ts engaged mercialers and wou a peak (HNTB North Cent At Cityp ptable alter its ng. Bein r comEngine an estim a thrust capac diameter, 140 tonne, ndoff ey ed Kaiser ws the consultantruction was ctions, withhave a majo way cutti engag en & Berge ity of 2,400 onstru 600hp shields high multistor is no acce route follo Cityp lace, MWRA e boxe designed by mme/cthes twoTamm g es the tonne via Needl their cons have itsa progra dsprisin project, million, were through Howar the 20 thrust have district, com . Both as ent and 62 built1988 April 19 passes development st to in be rams program.

Departm of $189 which Geoteyet essway ential Highway which is plans. by the ted in the Expr and resid second of LRT T ay the 7 DAR essw incorpora towers, ral Expr ct on the intense h Cent major impa of Nort nt, and nstruction way Departme d reco State High “Propose Texas by the

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The collapse of the it not back then? ty Construction Manager: under control after Authori• in now why was in-depth of an Water subjectTrent works at Heathrow is theSevern The to•that Taylor Woodrow station excavation &Safety l being Client:the sites.answer UK Health G portal H Hill & Sons tunnelling dnow Eurotunne Contractor: investigation by ting Engineofer:which is about October 1994. •The The geology shafts for transport the t:intende the UK. The storage facility is ners: faultless. ofClien • Design-build ENT:Engine its Desig Consulthe report projectoflooks vicinity of men and 1983 •(HSE), Geostore £20 million & Co of the site for the depth andtunnels in simple”, out JULYer:199 uced from rthe materials and for kept million yet.

• Contra carried the undertawhen and Ltd and)Executive Mowlem 78m deep project, m Contand introd racto (TML Balfour Beatty £15.1 is “amazin machinery ed ventilation, with John months taken king of ctors: for several according as awere maximu a joint 4 AND of • men s wereLink gly Calor Gas,x 1.8m diameter bore hole coal interest (6.5fissur started brought to the application Contractor: being collected firms to•appear sample to Tom The Residen hatlling systems a gh -Mancheby eight unlikely and) the 10.5km the wet FEBRUAR surface via two • Thyssen , and reamed is still Paterson, Wirtha reamer Trans 160m. Core is impressive Conoco with a with 60% consists t Mining Enginee tion (p56the the start 14.5km 40% t to build tunne were complete likely long spine roads /Pigott Consor l throu Carsing resources atton Material evidence examina Y 1996 contrac of legalthe tunnel r. The top ortium contracDesig formeticulous. ners: t. result remains highly readythe ct atr chalkproject ngs. to tunne possibility share, has and, with constructed in of alluvial tium: Shafts to remainin view, the drop coal d, causing l • Boldon 20m site and the identifie proceedings as a detail isCons headi in the ls) production onto cal hard planning to store g the and glacial longofaquedu rock well below the uppe geologi Tunne moved through the tunnel Tunne ard attention ethe mile) Drilling: Service point of connect Japan that from ofd thed’Étud y was to avoid the parties involved. a conveyor g foron next 200m the coal bearing deposits and scale ble landw severe ical the ortium in the crossthe itions slightly stages and instabilit tenderin into to au indicate and availa an event techn for the adit chalk strata. remarka is the Upper for transferring boreholes adjusted • Cons • Fairclo While (Bure ire has run sea e cond Tunnel through borings made clear toA conveyor system will struts and readilyion onto aon nt to be or to constru rom a which stretche conveyor ugh: Cavern hen Cretaceous mostly bly quickly. e: BETU whalings tion ofnotexcavat in Derbysh alignme d need for bring the coal the spine in either their under Channel Calais in Franc Therefore, it was ction the of driven onal the early The Francbe comple nisedup the two 1-in-4 ng props, s east under tunnels Jubile theunderlyi ms were roads and hauled Seae and to of be used behind area. es, andsyste McD with wouldshaft undersea avoiding s for the have In January nd to drifts to emerge years Lineinto the North attending an all-party-orga June to Proje affected Mottseries actor tunnelsrescue the surface could not Denmark ct team, as two compareddifficulti journalists These UK: diameter at the was up Exten in Engla 8km at Gascoigne1981, contr would r Gascoigne Wood 60m as Grit TBMs water h much end construction. angles r t, in From six explorat the of as European sion and West German Dove briefing in late ing granted by Woodplanning Frenc (Fig Fullface Ashove the London site where all the permiss andthemay at shallow may be to l and lt projec When JLE budg It is also gh the excavation visit and technical allionUnde large amount site the five that appo was inted ory borehol Glanford const2). y. natural coal mines are producing throucore handling, storage ease Strait cross pt and g tunne a difficu these dipping e, planned date the causes of et as well rgrou e of the by sched es, it was main series the access to ground water necessary to use the at Boroug runninThe ls. NATM becaus full ructio and loading facilities for the excavat Seikan schem passing h nCouncil capacity originally1970s attem questions about ndchalk was not mudstones, marin found as contains several ofby the ion of theexten to mana 1996, by ment n for d, and the lack of late 1980s, Selby nes as much. of etunnel. are located (Figs ule. Applic ardoftunne mporary uting.that chosen pressure theonLPG.” difficulty t, with ls bands thereof would thed equip 115,000 two approxi sion, twicegreat fashio awarde mudsto new ge costs will its 3 pre-gro lengths r landw deliver the of 1 aquifers tunne to d and m progr and marl g costing 10 The contain set expecte 2). the conte example. The UK along million cover the 16 km-lo caverns under mately ation ground acula nes, x 21.2m and very hard principle specifie and tonne had g contrac amm the collapse a 53-m tor itions of coal a year, long ded strata spect for more e for Conoco startowned is in isolated mostlyfrom d interbed assoc journalists however As soon as spine roads reached ng i.d. rail runnine tunnel,The tunnellin land When choosin sandstolong to do the onth y to contrac nts are: water for use red cond (Fig for the storage used ins and 164km Japan face bytothe public pressure, • that a higher funds Authorit st, except programm g a madeflint be answered. The Central UK the Electricity not ally setofitself by open first mine at Wistow, time. two 7.6m thensiltstone servic one containe on the to the 2). iated cost the survey 2was acts increa to in this storage m, fractuWater Clien Generating of sical section) against case liquid ing, it knew e ofsite for a tough use of drill+bla central achieveme n at thatfor twoletunnels, ter x ded with ation coal production and butane gas stratu t: JLE Board to a thorough briefing facility, the also specific Severn Trent 285psi, comprising an UK The propane interbed thewere ses i.d.

Gove at treated (252m LPG nearby Trans chose 100psi was was geophy Marl task.

Man the diame were by from calls (Fig excav notab visit power the A , It a it rnme ted , high began 14 to of 4.8m propane it had geology is 1). Site large stations. port throu confirm needed agem the Lond to As work began and with tunnelling of Chalk ber. tances, nt Depa soon weak Mowlem most investig or thertmen 15.4m time tocham large 55m 1).

Two other4.8km, ent team civilation and a liquefy the projec perhaps Frenc and hvice versa. current progress the spine as theimporta Unde theconnec bids. In view project's 30psi to liquefy on gh contain immediately constructio let in late short d in the impermeable, John wide the continuing to overthe design of circums at xthe same In the interim rground on the first nt conside the other out due to success from the t ation ofr pipeline for sections of roads t’s public which • Cont and later the the conveyors connect the remaining million contrac butane, shaft(Fig ingmajor 1993 ation n contrdepend of sea cross excav it. The 3.6km and was aligne excluded Ltd expected underground into various le for rapid also scarried under ally an in the ractorsthus a, signs t to sinkand • Excavdiamete spineof ng acces Itsfundin £2 access “Oneration. four mines. acts s ity ofpresence how borings. During at the ation, ls under e problems for investigtunne shieldwill transport aquifers a great natural is gener fourconst g is grant tworoads deep 140m of the most and tunnel of substan access for each highly suitabzones awith major geologi was to modifi both Knowing exactly pal worki r aspects engin ructio 3km of the 1.6km x 1.6m specify aon-going is ed. extent 66m which from essential. shafts, rail more extensiv the cavern, was n work tial their desig main site eers: See cal propert cation minesalong startecoal us rock on impor used again ute to red as they come andThe south drift decided to ader works. a shorterthe princiing .

“Unlike almost and three enginee gases, excavation d. n-bu on line andawarde ies. Petroleu tunnellin All following the longto land By from tunnel is being drivenThyssen . Roadhe current quality of workmanship clauses other tant explore inclay en-ro faulting, it was /Pigott Consor muck homogeneoalthough fractu be anticipated There is also side as consult sea of sever the contr dtheto end stage, g jobs, we all following page ild behind alignmeasily const the of form, themore m we 500m ion method best the the tunnelling the site. what the 5.8m diameter borings soft in gault end. The headings. to al of introdseeping option, three under from with stored welcom tium.ructio the ent 5th Januaare ster.

Nine s Hill t to two lofterminal based excavat in act es for eachmachines tunnel document water takes sump entaryCastleadjacen tunnelling, inflows were Robbins TBMborehol uced into surface e the sight downstream for itsof Manche supervision differs in ntheir liquefied workdeadservices ry liquefied red the total 230-w Tunne construction with be was was in a large supplem neveran average of stratum headings. The will based cavern landward tempera 1996, the by eithercond workscorrid and end itions levelH Hill & Sons continue!” into the were conside need to cased about 100m/wk. the collapse may Channel was moved and or were orted to the scheme eek corrid longation it was the ground high waterthe Chalk Marl contr lowering , their is a fortransp on confess Strathclyde drilled or by compre programm week ture 117 of of Anderson Theconven below seais G or beingprayofit up to 90m the UKOne portal y booms equipment would was going on before Boldon north where detail were made.

ICE ed Paterso conveyor by also is: included surface originall the imple actor in the Drilling ationartthat under explained in some tunnel, some 70m parallel, itsion ssion.would be stipulThe Souththe and shaft out e and,excav Site investig l Coal Board n. equivalent three muck was wide, the Tunnel Following a maximum 115m d. Tunnelling it is usual from of site andentall using portals grounad 1979 incorporates oil well type al ment is being 57 xtional 75% comp m of the the pump known, but it was boun be ment On the excavated using line ed to Nationa plishm theselectio times the during to appro to ation to store 16mm stratum through progressed this out in familiar sectio d to accep of speci area of surface steel ropedrilling ydistance m3 l some the seabe ng incarried a Titan 134 roadheader The the botto es water along and accom flamepr alignm themanin accel for thet caverns nOflies in finding e oofed lete. refrigerated provid cords rig. n was tunnels are going detail how work now being ximately downhil across the full Worthwhen an the eratio beneath making about half and ing width£4.5 ity of the abou tanks rather 4.5 ,million the manya ent depth. the tunnels The JLE to worki available. of deep borehol whose water is sufficien of themillion d withly at a1mlarge intervals tunnellin pressure logistical necessary servic site n progr 30mm thick the rate of progress was awarde original. slurrie and 75m suited belt.g The UK ds as strata, with the possibil t amm vessels. tCheape and that it was sinking standar contrac planned • The to containfor contr Proje thanshow inflow meth d to Fairclou Anderson constructio the in nso readily at Strathclyde the ce. is different from the about 50m/wk. Coal sal in holes highly ctt team ct, general in distan e minim olling to great the LPG themis under ods availa was gh, the three long be pract r stillthe Cable Belt cost t 1km Measures tried and side, running cannot be extractedfive tenders. Geosto nlowest the aquedufor dispo as groun systems is the as but of kably ued conveyor Coal shallow to to estim tered. while abou super UK of well al make pressur store not contr reaso icable in d move ble of appo remar until the cross theundergr ates North Tunnel is are, a actor were the ising vising e in larger additiong pond ed seepag nable,” on the ct scheme French were particularly These contin of e being encounspecified the grouting adit connecting ment inted of settle e accep steel licencee ment water from usedcost ound geology Robbins pumpin company comp changed ropes reinforced Project NATM with several settlin rescue methan capacit said or trains, of the the two conveyor s from which allow facilities on JLE. technTBM and g , nearly doubles y Mike r also belt spine roads and ted the cavern consu Giant excavation ls Geostock, oir and Aquedu tunnels.

Mana on ation of In some groundshaft the letedwhich . Liquefie ical have designed speed with two all have What had al advances most extensive ltingroadheader Smith the bore hole connecting of prohibitive. time accesallowThe steel been cases ton Reserv ed Enginee theof origin canno d ger ropes and supervis undersea , JLE’s for Cons tunnelling 1. Carsing gases • Applic been success engineers and y for rapid and tunne sealed, stableTo and this may To comp 57mm has pressur excavation start,tothe most obvious, ologic the mine above is diameter prepa allow grouting fully tstored the same for thethe ed a of several require extensiv supporting tunnel regime to ensure modification tructio /week the detail Selby ensate red thection al in completed. constru predic high speed 428mFig used initialllex chambers operatio the techn to tunnel spine be jeopa lightweight ede indesig LPG caverns On leached cavities n. cross while at cing service roads projecgroundw alling area ted settle 1in-thick contr e for areas clearly most expensive, is the The um and breaking 60mWistow mine t progr ater “Wens and rdised under ground The steel through which act fordocu of the chalkbelt. ns our , includin a projec of many in salt ropes ment in northern a maxim a maximum 8h high,alteratio the comp ground marsh of works record came online in April by s ammregime are formed g one deposit conditiotns spliced the advan excavation where d amount t oftogether there but e to around grout n of the may still At ment this in size the original scope itsyears side of findingcontr ation. under to form an France, final ng s that to be almos the ol. The event have 14.5km forand enginee isrope suitable the caverns injection Cliff. This n and a purpose the consult with the expectethree stages:toadvancex 30m deep cofferdam built in the prove methods of the the UK 7 days/week with eek) buildi are ction r. Associa endless provelength, been the dealtwo acceleratio constru geology comp concurrent ber, which had of the conveyor at withinof water -built undergr each in too ing n its contr will statio espeare groun tedOne side. unfor y be lexity, diameter come intoby of the most shift/w the tunnel; contrac and nwater no easy l construction galleries eseen the of the airport This is done ound of its clause grouting at Shak pal working (24h/day, maintenance kindfacility mont task, as longest used to curtains segmentall water. ation inactua their own. d treatment over cham before arriva operation of driving Central in Octob ts include of a new adver Terminal Area (CTA the se in difficu has betwee isl usefu Europe. excav methoabove, TBMs lties.Paterson hs when South Killingho e River Humbe LPGerjetty concrete and radial Two effect explaine was“The n caverns m. The ds. used 1994onof permeation the princi of the six downtime 3) to almost totally ure in advance Similarly, the collap over the grouting geology were being d:the recov lness complete e servic are built; Terminals r, on the lme, neither At the ive NATMenough ed. 1, 2 and site non-bolted l of o.d. 8,036 on JLE on ery progr of the se must be compet connect the and pipeline machines. ges and press negotiated. water as the rings the marin grouting, grouting sunrelated, excavation gallery strengthen launch a fully to include remove the extent grouting tunnel amm muck will also km each is es has been complet nor Airport which facility to expecte sea tunne 22km of 179m/week ent ” concu work extensiv encompass and TBM allow the Conoco loose a to stabilise Express but of course Only by cross passa had to share cing after the lining vs be necessa and 18.77 excavat Settleeme andd to complete lined under ll average was l south. water disturbed ground. grouting of the the roadhead refinery Rail Link rrent, er ion and the Because the geologic Heath compensat an imme and ry.

17.36km bearing collapse and the rowmore ducts also with the advan Since limited thent con requirem diate al tunne l excavation the site ng properti introduction ion huge Groun the tunnel, best overa e running tunne rn slurry and this are groun of ent, and l porta drivesstanding at the edge relievi project. the more d move support effect so es grout A Titan E205 trolthe of the Jubile responsible progress l to n times TBM, ngs. marin of predic of ing for mitiga d, bay has been importa nt, a sgeotech As ment induc roadheader e project side, mode pressurised econom consecutive interc job, Mowlemscale be appreciated. "The upper the UK in the from porta reaction, ratesbeen ted transportatio g tunnel headi Four which South ic its contr one French establis excavatingteam volun Tunnel the ed its that bid the couldWork by excav Tunnel have hed,ept groun nical volume losses ting and piezome work ce (EPB) runnin On the actors the 9m wide tarily instru the JLE projecof the most critica eight firms tender. ters ation has Channel cross marine water-bearing ground Ofl the to measur equippeddmove Waterloo mining to ure balan withments x l t team. ctedtop benea was soft outer lowest 20m second as they and e ground four hand 53km long and Lond stop NATM 5m high thethe and through and The Line, concerns for the earth press many latera Com stabilized by 1.2m heading with occur. ducts won of the water integrity th ,some work at ber 1981 gravels d the rescue shaft • The x plishe with visible pen is supported and running 30m deep central on years.

Septem section and safetyon Bridge to of the oldest ure relief access bands important as it does 60m diameter Compensat sation grou ls. in shaft, press accom original piles which interlock ted in four review of marl started 1km of 19m diameter tunne Fig 1. Trace of the Geological , histor of the and stages of diameter the is ion grout one toSecant ting flint a NATM ges and main bored ed on the different d to be comple icallyand works.

Alan Powderham, under and subjected prestigious, the only work had most present designe for JLE comp in the chalk ing is About centres," explained all of which were access shafts superimpos passa areas of plan was 1.06m tunnels, and to the techniques Mowlem portals the three at that e platform limitation principally managemelex exercise London, linking of the Foundations time and been completed NATM The surveying from the four to ensur tolerances most stringent concourse and outer dersDirector Managing work collapsed MacDonald advanced s employed drive a tunne ngmain tunnels lyde roadhea decision-m nt and co-op in multi-level the damage the works restarted although revise the delay headi Division of Mott lling projec ever before • The excavation when Strathc system Geotechnical tunnel d or Steel in imposed had a t in the Anderson provided aking based erative all-pa representative on guidance Asses In fact using ct sea and Grosven damaging due course, on city. rty lead sea. in designer's six under Aquedu and Markham tonthe convened predicted sments of all PortaltheC instrument by extensive on information effect on under the mounte that Carsing Compens servicdein Solutions Team buildings started at the so-called in 1mm ng lly meet ation the D French geote of the 10.5km ation and engineer the s Tunnelli to actua the within B settle analysis. collapse and and m on chnical did grouting 12.4km shields. ment conto the 350m cross section computer-b and at Portals immediately following the “The of the UK undergroun arrays dinal and Harris, ur along aim,” way forward. "The junction was within February 1982, at A in April. under ased d route a Direc in economic Fig 2. Longitu the West a safe and headings level. tor of the explained David e finally defines and the princi early stage,Clay below is supported by 900mm tunnel mins marin on an March, at a company ter area the pal geote 60mm London d decided conditions, on comp installed which step in GCG as It was line and ents of create d ground diameterplan contiguous piles ensation chnical advis from five establishmUK side which a predicte er to of the 20m below, the grouting, temporary viewcliffs • The comprehensive continue a further chalk andion, on the “is to keep JLE from, ing grouting m3 te a excavat capping beam at formula lagoons the white el head tomillion the method of Secant piles. shafts With "A substantial foot of ce Tunn rating the some 3.75 incorpo at the ent lining. surface forms a rigid concrete collar UK Servi and tightly site for and perman ground the main re for the er, disposal what is an small roof support factu Employ in all the 79piles together. manu linking ent of the were Report site. of muck TBM in in both the recovery ideas ies agreem of CIRIA working s’ "Originally, Howden a large endations t Practice high confined ent casting factorrecomm based on excavating ands of ing - Improved Contrac instinctively segm approach Fig 1. Plan of the ‘Tunnell x 65m," said Powderham.

• The ries where thoussegm ents were Gascoigne Wood and the general nts. 65m box of about y drifts and the five mine followed lining count shaft sites; UK factor contract documewere to tunnel Thewere tial in the Inset: Fig 2. Main rated precision at high rats. incorpo design features a poten h sections of the tunnel for day the need produced Grain had Althoug per ent rock, Isle of d near in compet segments on the driven755 was expecte be 4,42, of 1,152 required ate roof support output ced the .immedi and produ within 3.5 years on of the 37 42 segments ation now goingand lengths install units • The thousands of and other g, track many cablin ical of electr

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tax in the sewerage the water and served by t rates for and cities the lowes clean 1997 one :ofMAY 43 towns project to REPORT had paid payers of VISIT nians SITE Bosto ar, $6.1 billion when rate flowing

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STUDY: Application of a TBM for developme in North Yorkshire nt of one of the was the first use twin spine roads of a TBM on a demonstrated to link five coal mining project the significant mines in the UK. The 5.8m advantages of Robbins went on diameter Robbins the technique to supply TBMs to over traditional mine CASE operations the roadheader excavation TBM non-circular TBM STUDYworld for excavating over. Most recently : Excava rectangula Robbins has developed and r cross sections. an estima tion of the ted half the first a new cost of creatin ever purpose built also provid LPG storag ed greate g the same r security e cavern JUNE 1983 storage capac s in the UK for these CASE STUD vital infrastr ity in tanks in on the surface the 1980s were built Y: JLE, the ucture facilities.

SITE VISIT turbulent at . Underground REPORT: MARC London times. storage Excavatio including Undergrou H 1984 n the Big nd Jubil and Lond Ben cloc progressed ee Line under on Bridg k towe Extension or alon services r and the gside project, to area e mainline railw Houses lived limits of s of south of Parlia some of the ay statio the most impo through excit ment; ns; and created excavatio Underground and east Lond ing passed new metr rtant landmark as well as on, system. n work under the mos s Controllin which until o then had the River Tham stations unde s of the city, he Selby coal t critical collapse on labyrinth mine complex the conc g excavatio chal rema es of in leng four time r the Waterloo unlined closedYorkshire was n and urrent es tunnels, driven designed by the settlemen ined outside s to bring Heathrow • Client: UK National SITE VISIcircuit and loading together with UK National Coal the tech t and man Express metro beneath the in chalk Coalsome man Board Board (NCB) TS AND nica terminals 190m to connect five aging Rail Link flatland on tankers for rail and aging the • Consultant: bank ABRatIDG separate mine sites the impa l construction of the River National Coal the budg Immingham. project road south - at Board Wistow, Stilling Fleet, Humber, ED FRO ct of the in Octo • Client:et and the will be used first mined Riccall, Whitemoor as• the Contractor: statio ber 1994 M TWO Calor Gas M&E insta Cementatio and North Selby. underground n Geology petroleum Ltd were amo n JLE SUP• Consul llations.

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1994 Rail Link in October the Heathrow Express prosecution excavations on world. The criminal of the NATM station UK and across the the works and CASE STUDY: Collapse ns for the tunnelling industry in the later, after working on to recover during ramificatio years ns made had high impact d engineer four and its design-builence of how decisio s in the shields experi trial of the contractor to injury. roadheader anticipated insult a salient added ted that the the project, uct was than complete gton aqued for the project predic more water last. The g rock and long Carsin or drill+b biddin harder 10.5km mining ctors The when amounts a to hand turn ided CASE STUDY: seriously wrong. Contra as. They were right s and to keep large 1996 , prov JUNE eader go Its essed air REPORT: roadh in 1998 compr cts. before Christm theirces SITEtoVISIT design can upservi under giverail cedproje on the hillside advanture was four drives would be against public infrastruc out of the ed to eadere shield, hmarks mega forced three dwhich kept its roadh of futur d as benc and open face, funding ingplete lems, stan remain l. el, com ion and ted prob contro nizat under nnel Tunn water , orga documen ofning The Cha e plan its well well as STUDY: vativ H 1983 CASE el for the inno successes, as RT: MARC VISIT REPO project in truction SITEkes.

• Client: BAA role mod mista occurred on the that cons ar collapse ing for the owner: d simil job in the focus the mind, outstand rs will avoi 1994 will always • Consulting Engineer hatever jinxed the to be well October othe - if it is being achieved Mott MacDonald which beginning, all appears question remains

Digital format: Special Edition

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Digital format: Special Edition

Canada Focus N aga a hyd o duc on d ve Aqsue Ca ng on ec po M W

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SPEC A ED T ON FOCUS CANADA CASE STUD ES

TunnelTalk National Special Editions and Case Studies Construct on of new underground nfrastructure s based on the exper ence of the past w th new approaches to pro ect procurement fund ng and p ann ng deve oped and the techno ogy of excavat on methods and mater a s serv ces and support too s ntroduced Dur ng a 41-year career as a ourna st and reporter n the nternat ona ndustry Tunne Ta k Pub sher and Execut ve Ed tor Shan Wa s has pub shed art c es about the most format ve of these pro ects and deve opments Th s wea th of h stor c nformat on s nce 1982 s drawn together n our ser es of Nat ona Spec a Ed t ons and Case Stud es w th ssues pub shed to date for USA Vo 1 the UK Denmark and Canada and more to fo ow

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