ABSTRACT
Launch shafts used to launch tunnel boring machine (TBM) must accommodate the launching operation which includes TBM lowering, assembling, and launching. The functional requirement affects the proposed geometry, dimensions, and type of retaining structure. Soil conditions add complexity to the design. In this paper, the design of a launch shaft using 2D and 3D FEM analysis is reviewed and verified using field monitoring data. The 50m deep rectangular shaft is constructed in residual soils and rocks of Bukit Timah Centre (BTC) of Singapore. The earth retaining structures comprises diaphragm wall with reinforced concrete strut and waler to retain upper shaft at the residual soil layers, and mined shaft for excavation at deeper rock layers. The toe stability of diaphragm wall at the interface with the rock and overall performance of the ERSS including wall deflections and groundwater response are reviewed using field monitoring data.
