In the London Docklands Light Railway (DLR) Lewisham Extension tunnelling project, the contractor has utilised compensation grouting to remedy building settlements due to twin tunnel construction. However, the contractor needed to demonstrate that grout injection would not damage the tunnel lining. At the Schofield Centrifuge Centre, Cambridge, physical modelling of compensation grouting in dense dry sands was commissioned to clarify the effects of grouting depth, grouting width, and separation between grouting depth and tunnel crown on segmental lining deformations and ground movements above the grouted areas. The measured ultimate uplift resistance is compared with an upper bound plastic solution. An approximate pressure distribution mechanism is also presented to calculate lining deformations due to grouting.
The DLR Lewisham Extension was constructed in South East London where ground strata are Made Ground underlain by Terrace Gravel, Woolwich & Reading Beds (now known as Lambeth Beds), and Thanet Sands. A Slurry Shield Tunnel Boring Machine was employed to excavate twin tunnels of 5.85m diameter. The tunnel cover (C) ranged from 9 to 15m, and the separation (Y) between grout injection and the tunnel crown is 2 to 5m. More details about the construction site can be found from Lee et al. (1999) and Sugiyama et al. (1999). Figure 1 and Figure 2 show the site layout and the typical compensation grouting array beneath a building, Royal Hill Court. The contractor, Nishimatsu Construction Ltd, used compensation grouting to remedy settlements and tilting of buildings due to twin tunnel construction. In order to understand the effects of compensation grouting on ground movements and tunnel lining deformation, a series of centrifuge tests in dense dry sand was conducted. The measured ground movements and lining deformations from various centrifuge tests are presented in this paper.
