Observations of ground movements during tunnel construction by slurry shield method at the Docklands Light Railway Lewisham Extension-East London

Abstract

This paper describes monitoring results of ground movements due to slurry shield tunnelling on the Docklands Light Railway Lewisham Extension (hereinafter referred to as DLR). The DLR tunnels (twin bored tunnels) run from Island Gardens Station to Greenwich Station in East London, passing under the River Thames, a distance of around 4.2 km. The construction of the tunnels, which were at shallow depth, needed an extensive appraisal of the potential damage induced by ground movements to the overlying and underground structures. Therefore, in order to effectively minimize the ground movements, a slurry shield machine with a diameter of 5.85 m was employed. Careful control of excavation was carried out during shield tunnel construction. As a result, the slurry shield tunnelling method in Woolwich and Reading Beds by well controlled monitoring was successfully conducted, leading to volume losses less than 1.0%. This paper focuses on the ground surface movements, particularly the transverse and longitudinal settlement profiles, and volume losses during shield tunnel construction, in relation to the ground conditions. Based on the monitoring results, combined with previous centrifuge model test results and other field monitoring data, practical methods to appropriately predict ground movements due to shield tunnelling are proposed.