CROSSRAIL GEOTECHNICAL SERIES – 1
Preparing the ground for Crossrail
Aug 2010
Patrick Reynolds, Freelance Reporter
With major tunnelling contracts for Crossrail to be awarded soon, TunnelTalk begins a series of articles looking at the geotechnical preparations for the extensive urban excavations and to be undertaken the tough settlement control regimes being established. Following this introduction, the site investigation and geological studies are covered in Article 2 and settlement control measures for the project is described in Article 3. Future articles will expand the topic, explore different aspects in greater detail and report on performance during project progress.
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Transport Secretary (right) confirms government support during a recent project visit and warns of tight cost control (James Reid Photography)
- The new UK Government has signalled its support for the £15.9 billion (approximately US$25 billion) Crossrail transport project in London. Following the general election, in early May, Britain had waited to hear the first proposals on how the new coalition Government plans to execute large-scale cost cuts to reduce debt and significantly improve the national balance sheet.
- The construction industry is concerned over potential threats to public spending and some clarity was needed over the potential impact on Crossrail, the country's biggest project, which is partly Government funded. Under the previous Government, work had progressed to have main construction underway and the major tunnelling contracts are expected to be awarded soon. In confirming that infrastructure investment will be important to the country's future economic growth, however the new Government adds the rider that, as with everything else it is involved with, there is a fresh spotlight on costs.
- "We live in difficult economic times," said Transport Secretary, Philip Hammond, when he visited Crossrail in June. He added, "we must ensure that every pound we invest is well spent. I am determined that this scheme remains affordable – Londoners, business and the taxpayer would expect nothing less."
- Planning for the transport scheme has been underway for years, including the extensive geotechnical site investigation work for the tunnels that will be bored below the heart of the capital. The effort is vital for not only the technical efficiency of the excavation works to be executed, and the tough settlement control regime to be established, but also in delivering the financial benefits they represent.
- The project
Crossrail is scheduled to introduce rail services in 2017-18 to increase the city's rail-based transport network capacity by 10%, cut commuting times, reduce congestion, support regeneration and boost the economy.
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Heavy-rail train services across London east-west via a tunnelled link directly beneath the centre of the city
- By tying into rail links far to the east and west of the capital, the scheme will bring full-size trains into the city to a string of brand-name destinations and underground interchange stations at Paddington, Bond Street, Tottenham Court Road, Liverpool Street and Canary Wharf and key stops at Farringdon, Whitechapel and Woolwich.
- The strategic value of the rail scheme has been long recognised but there has always been debate over its precise costs and benefits, and consequently, who should pay.
- In the mid-1990s there was a push for the initial vision for the project but momentum was lost.
- By 2001 there was renewed impetus and feasibility studies progressed to envisage the larger project, which was supported by the previous Government and taken forward.
- A Bill was submitted to Parliament in 2005 and Royal Assent was achieved in July 2008. The project, finally, could move into the delivery phase.
- Preparing to deliver Crossrail has been a long process of extensive studies and planning work, not least in terms of site investigation for the twin 6.2m i.d. (about 6.8m o.d.) running tunnels which, at a total of approximately 41.5km, are longer than conceived in the 1990s plan.
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Procurement time-line for the multi-billion Crossrail project
- According to the latest plan, the tunnels are to be bored by eight TBMs – six EPBMs and two slurry machines – in three running tunnel construction packages, two of which will undertake the majority of the twin tunnel route. The first TBM is to be launched in October 2011.
- The project also requires myriad large excavations for the many underground stations, passageways and shafts on the scheme, and the 21 cross passages that will connect the running tunnels. Work continues on an array of detailed design contracts already awarded to various consultants and engineering firms.
- Planning and management support is being provided to the core client team by two groups:
- • Programme Partner – Transcend, a JV of Aecom, CH2M Hill and Nicholls Group.
• Project Delivery Partner – Crossrail Central, a team of Bechtel, Halcrow and Systra. -
Tough settlement control
Given the city's congested and expensive urban environment, there has been long-term and significant effort made by the client, Crossrail Ltd, to establish a tough settlement control regime – tougher than those mandated for either of the two most recent and significant underground and TBM tunnelling rail schemes below the capital: the London Underground Jubilee Line Extension (JLE), and the Channel Tunnel Rail Link (CTRL) that carries high speed trains from the international terminus at St Pancras under the northern suburbs of London and on to the Channel Tunnel crossing to Paris and Brussels. Now known as High Speed One, or HS1, CTRL has been recently put up for sale by new the deficit-reducing UK Government with Eurotunnel, the operator of the Channel Tunnel, a front runner of the prospective buyers.
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Work began in 2009 with award of the Canary Wharf Station contract (Photo by Jeremy DeSouza)
- Crossrail has been able to draw upon the experiences and achievements of CTRL and JLE, but to help to further develop the controls and systems it will use, it has also been liaising with other major schemes underway internationally, including the Line 9 of Barcelona's metro in spain.
- The key controls will see a general cap of 1% on volume losses, doubling of both available grout and TBM power, section engineers having sole authority for starting and stopping the shield drives and ring building operations, and creation of a project-wide, real-time data gathering and management support system.
- TunnelTalk spoke earlier this year with Crossrail's Geotechnical Manager, Mike Black, and former Acting Head of Tunnels, Portals and Shafts, Neil Moss, about the site investigation studies and geology along the alignment, and the choices made for the settlement control regime, tunnelling management, and some key research projects. Site investigation and geological studies are covered in Article 2 and settlement control measures for the project are described in Article 3.
- Crossrail Geotechnical Series - 2: Site investigation and geological expectations - TunnelTalk, Aug 2010
Crossrail Geotechnical Series - 3: Settlement control measures - TunnelTalk, Aug 2010
Monitoring contract for Crossrail - TunnelTalk, June 2010
Shortlist for Crossrail running tunnels contracts - TunnelTalk, Dec 2009
Crossrail launches construction phase - TunnelTalk, Aug 2009
Crossrail management mobilized - TunnelTalk, May 2009
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