At Halfway Mark, $24-Billion U.K. Crossrail Project Back on Track
The construction of tunnels and stations beneath central London as part of a $24-billion Crossrail project has hit the halfway mark on time and budget. The successes are feeding into ongoing planning for over $60 billion worth of high-speed rail.
"The industry is enjoying a renaissance and a reputation for delivering these projects on time and cost [to] a very, very high quality," says Andrew Wolstenholme, chief executive officer of Crossrail Ltd. (CRL), the city's project owner. Noting lessons learned on construction for the London Olympics in 2012, the Heathrow airport's Terminal Five project in 2008 and the London-Channel Tunnel high-speed line (HS1) in 2007, he adds, "We have a responsibility to pass that on to High Speed 2."
Like Crossrail, High Speed 2 (HS2) will entail moving mountains of materials and spoil in and out of the congested city. Crossrail experience in controlling ground settlement under numerous buildings will inform HS2, says Ailie MacAdam, CRL's delivery director and a senior vice president at Bechtel Inc., San Francisco. "We are seeing a third of the movement that was anticipated," she says. "The control on these tunnel-boring machines is extraordinary." With the right incentives, the supply chain, including design firms, "could do some really innovative stuff, if they are enabled," MacAdam adds.
An estimated 200 million annual passengers will use Crossrail when it opens in 2018, increasing by 10% the city's rail capacity, according to CRL. The 118-kilometer east-west line, between Abbey Wood and Heathrow airport, includes the tunnel section in central London, which accounts for most of the investment. Underground stations are being built in the central section at existing transportation hubs.
After the project fell behind schedule in 2012, when tunneling began, work is now at the midpoint. "We are ahead of the curve," Wolstenholme says. "Deployments of that size always take slightly longer than you think," he says.
"We've been spending over $165 million … every four weeks for the last year," adds MacAdam. Bechtel supplies around 200 of CRL's 600 staff, who manage and monitor a vast array of firms led by over 20 main contractors. MacAdam says there haven't been many major snags. She notes the unexpected discovery, in 2012, of piles, which delayed shaft construction at Liverpool Street, and the partial collapse of spoil-loading equipment at Royal Oak, also that year, which halted tunneling for three weeks.
Construction has focused on some $2.3 billion worth of 6.2-meter-dia, segmental concrete-lined twin tunnels. CRL specified and paid for the project's eight 7.1-m-dia TBMs. Germany's Herrenknecht A.G. won contracts to supply all six earth-pressure-balance (EPB) machines and two slurry TBMs—all eight costing about $16.4 million each. The EPBs were selected for the clay, sand and gravels that run through most of the route. Wet, chalky ground under the River Thames calls for the slurry machines.
The first TBM to deploy completed—in October, ahead of schedule—an 18-month drive from a portal at Royal Oak to Farringdon, says Tom Tagg, managing director of a joint venture of the U.K.'s BAM Nuttall Ltd. and Kier Construction Ltd. and Spain's Ferrovial Agroman S.A. The JV is building the western 6.2 km of the twin tunnels, including widening the running tunnels at the Tottenham Court Road and Bond Street stations and creating platforms using excavators and the sprayed concrete lining (SCL) technique. SCL is being used on a total of 12 km of platform tunnels, passages and other sections.
A joint venture (DSJV) between Dragados S.A., Madrid—which owns 90% of the JV—and Ireland's John Sisk & Sons, is excavating Crossrail's longest tunnels. It procured four TBMs for the 8.3-km-long drives from Farringdon via Stepney Green to the Limmo portal and a 2.7-km spur to Pudding Mill Lane. When the first machine on the spur reaches Stepney Green, around April, DSJV will take it by road to Limmo for the 0.9-km drive to Victoria dock. "We will be dismantling, transporting and installing a TBM in central London, which is a challenge," says Paco Gonzalez, DSJV project director.
Gonzalez says progress has been good, considering the TBMs must stop every couple of months at stations or caverns under construction. The first two TBMs have averaged seven 1.6-m-wide rings per day; a third machine achieved 10 rings per day. "We have reached one kilometer in a month," he adds.
DSJV runs two production lines to cast the eight segments needed for each of the contract's 13,700 lining rings at Chatham, which is 50 km away. "We are making one segment every seven minutes," says Gonzalez. Water transportation accounts for some 90% of segment deliveries to DSJV's tunnel portals and for spoil removal. Most of the total project's 6.5 million tonnes of spoil leaves London by boat or train, and 75% of it is being used to build a nature reserve up the coast.
DSJV's first TBM left the Limmo portal in late 2012 and broke into the huge cavern at Stepney Green last November. The trumpet-shaped cavern will contain the junction at which trains branch south to Woolwich and along the spur to Stratford. The 40-m-deep cavern is more than 100 m long and widenes to 17 m from nearly 14 m. It is linked to a twin cavern by a six-floor-deep shaft. Both were completed last August. The TBM is now headed for Whitechapel.
To limit movements beneath the buildings above, tunnelers must keep ground volume loss generally below 1% by using techniques such as controlling TBM face pressures. With fine controls, good instrumentation and real-time data, "we are seeing a third of the movement that was anticipated," says MacAdam.
Stations and Software
Stations are essentially concrete boxes built within slurry trench walls at either end of the 240-m-long platform tunnels, says Graham Williams, a station project manager with Arup Group Ltd. Arup, in a JV with WS Atkins plc, designed three stations. Platform tunnels at five stations were mined using SCL. At Bond Street and Tottenham Court Road, the running tunnels are being built first and widened with SCL, to form platform spaces.
As some 9,000 workers toil on Crossrail, CRL is storing all the digital data used in design and construction to help the future operator, a unit of Transport for London, maintain the assets. "We are building two Crossrails … the physical asset and a digital model," says Wolstenholme.
Since detailed work began in 2008, all the project's 25 main design firms have used the same 3D model systems, says Malcolm Taylor, CRL's head of technical information. CRL now owns and controls all electronic data generated by its designers and by nearly 100 constructing and logistics firms. That equals over a million electronic documents and even more CAD files.
Bentley Systems Inc., Exton, Pa., is providing all the software to Crossrail. Bentley also runs a Crossrail Information Academy at its central London office to train contractors in the use of building information modeling. Bentley worked with CRL to develop a new tool called Asset Painter to help manage the rail network's one million assets in a central data hub.
Design teams have handed their 3D and sometimes 4D model data to CLR, says Tony Bevan, an Atkins CAD manager, and CLR wants contractors to do the same. The response, however, has been mixed. "We are not using BIM yet," says Gonzalez, though his team is preparing a proposal.
"The industry is only in its infancy in understanding the value to be had in delivering the digital model," says Wolstenholme. "If that digital model is configured and organized in such a way that you can hand over the assets as a life-cycle model, then this has much more value to the end user."
