Deformation control of operating tunnels induced by deep excavation of overlying metro

The excavation-induced deformation of pipelines is one of the top environmental concerns for excavations in urban areas. The foundation pit at the exit to Yanggao Road Station Exit, which is part of the second stage project of Shanghai Metro line No. 9, overlies a Φ3000 mm-operating power tunnel. To prevent the possible tunnel damage due to the excessive deformation, the soils are strengthened by using the metro jet system(MJS) method, the blocks are constructed by means of the block excavation, and the FEM-based tunnel deformation prediction is adopted. In addition, a real-time tunnel deformation monitoring system consisting of static hydraulic pipes, crack meters and signal transmission equipments is also adopted. The monitoring data indicate that the soil treatment by the MJS method is an effective way for deformation control, and that the state of the tunnel can be captured by the tunnel deformation monitoring system in the very first time, which therefore enables the implementation of feed-back construction strategy.