Ground Settlement Behaviour In Chalk Due To TBM Excavations

Summary

In Crossrail project contract C310, two new tunnels the Thames Tunnel (westbound and eastbound) will be constructed between Plumstead portal and North Woolwich portal. The Thames Tunnel is 2.6 km long and about 15 m below the existing Thames river bed. Construction of Plumstead portal commenced in 2011 and completed in 2012 for the westbound TBM launching in January 2013 and eastbound TBM launching in May 2013. The construction of North Woolwich portal has begun in early 2012 in order to receive the first TBM in 2014. The running tunnels will be constructed predominantly through chalk. Two slurry TBM machines, Sophia and Mary named after the wives of Marc Isambard Brunel and Isambard Kingdom Brunel will be adopted for the sake of the existing ground condition majority in chalk. The degree of settlement control is one of the prerequisites for tunnelling design for the consequent risk of damage to third-party assets. To obtain the surface and sub-surface settlement profile and corresponding volume loss due to the tunnel constructions against the predictions, various instrumentation and monitoring systems, namely from typical manual levelling studs to advanced automated precise hydrostatic water cell system, are used. This paper is to compare the observed tunnelling-induced ground settlements with the predicted by empirical methods. This study will be a valuable addition to the available literature on ground settlements in chalk, particularly since there are so few case histories available and the predictions of volume loss are often conservative as a result.