The Response of London Clay to Full-Face TBM Tunnelling at West Ham, London

摘要

A 2.8 metre outer diameter cable tunnel, 1.75km in length has been driven using a closed face Tunnel Boring Machine (TBM), from West Ham to the Greenwich Peninsula in East London, to provide power to the site of the Millennium Dome. The choice of tunnelling to install electricity cables, rather than open trenching techniques was made in order to minimise the potential disruption in London's congested urban environment. The construction of cable tunnels for the client (London Electricity plc) has facilitated the on-going modernisation programme of this important element of the city's infrastructure. A recent feasibility study carried out for a similar length of cable tunnel indicated that construction costs for a tunnel option could be up to twice that of traditional trenching techniques, while the construction programme was of a comparable duration. However, considerable advantages would be realised as the construction programme was much more predictable. Problems such as clashes with existing services, environmental effects, maintenance requirements, traffic disruption and potentially litigious public relations difficulties could be avoided. In order to gain field data relating to the behaviour of London Clay around an advancing tunnel and at the same time to progress current in-house research initiatives, Brown & Root took the opportunity to establish a monitoring site in advance of the tunnel construction. Surface and sub-surface instrumentation was installed at the location of a disused timber merchant's yard approximately 400 metres from the start of the drive. Information was sought on the inter-relationship between tunnel construction processes and ground response in order to improve specifications and to enhance construction control. The data collected will be used in the calibration of finite element and analytical methods being developed by Brown & Root in collaboration with Cambridge University. The West Ham to Greenwich cable tunnel passes at a depth of about 13.5 metres (axis level -11.5m OD) below active and derelict light industrial and dock land developments, the River Lee, which is a major tributary to the Thames and a number of major transportation routes through London. These include the A13 trunk road, the Docklands Light Railway and the River Thames itself. The following paper describes an assessment of the behaviour of London Clay during the passage of the TBM. Representative plots of the results and interpretation relevant to future prediction of ground response to tunnelling using this type of TBM are also described.