ABSTRACT
Ground response to the construction of twin 7.1m diameter Crossrail tunnels using earth pressure balance machines (EPBMs) in London Clay was measured at a ‘greenfield’ instrumented site in Hyde Park, London. Short-term surface and subsurface ground displacements and pore water pressure changes were measured, the results from which have already been analysed and reported in detail. The field measurements have continued at the same instrumentation site for six and a half years after completion of construction. The post-construction measurements of subsurface ground displacements and pore water pressure changes around the newly constructed tunnels are presented and discussed. The ground above the tunnels is settling at an average rate of 1-2 mm per year at the end of the 6.5-year period. Pore water pressures in the ground around the tunnels have not returned to the pre-construction levels and are not tending to, indicating that the tunnels are draining the London Clay, even with the presence of a 0.15-m thick grout annulus around the segmental precast concrete linings and waterproofing measures. The post-construction measurements presented give valuable insight into the long-term ground response following tunnel construction with EPBMs in stiff clays.
