Construction of Waterloo Station upper level tunnels, Jubilee Line Extension Project

The construction risks associated with the complex, shallow, large diameter, close proximity layout of the upper level tunnels at Waterloo Station on Jubilee Line Extension Project Contract 102 were increased by the potential impact of compensation grouting. The Contract required this method of ground treatment to minimise the effects of excavation related settlement on the overlying main line railway station structures. In the absence of directly relevant previous experience, the potential adverse impact of the grouting, compounded by other works related effects on the traditional tunnels, needed to be evaluated and design assumptions had to be updated systematically using an observational approach during construction. The systems in place, their control and the rapid interpretation of the results, proved highly effective in producing a reliable process for ensuring stability and keeping to acceptable settlement and tunnel convergence tolerances. These were achieved by excavating for and installing optimal temporary supports at the appropriate times and configuring efficient compensation grout injection patterns. Large quantities of monitoring data were collected during this process. Anticipated mechanisms controlling the impact of compensation grouting on the tunnels are discussed and monitoring data of ground movements, tunnel deflections and temporary works loading is presented.