THE USE OF COMPENSATION GROUTING IN TUNNELLING: A CASE STUDY

At the London Docklands Light Railway Lewisham Extension (DLR-LWE) twin tunnelling project, compensation grouting was carried out beneath sensitive structures to prevent excessive settlement due to tunnelling. However, excessive grout injections might exert extra loads on the tunnels underneath. This issue has become a major concern for tunnelling and grouting contractors after a report by the UK's Health and Safety Executive in 2000, which listed grouting force as one of the possible factors that might have caused the collapse of the London Heathrow Express tunnels in 1994. This paper presents the extensive field monitoring data compiled by the tunnelling contractor on surface and building settlements as well as tunnel lining deformations caused by compensation grouting. It will be shown that the final corrected building settlements, incorporating compensation grouting, were about 5 mm. In the case of greenfield settlement the maximum observed settlement was less than 15 mm, a criterion specified by Lond...