Numerical Simulation of the Face Stability of Shield Tunnel under Tidal Condition

The excavation face stability of shield tunnel under seepage condition was studied by 3D numerical simulation. By using elasto-plastic deformation/seepage finite element analysis, the deformation process when support pressure reduces from earth pressure at rest to limit state under seepage condition was obtained, and the failure mechanism of tunnel face and the limit support pressure were determined. The influence of the cohesion and friction angle of soil on the failure mechanism of tunnel face and limit support pressure under specific water table line were investigated. The results showed that the soil strength parameters affect the value of limit support pressure; however, only the friction angle of soil would change the failure mechanism obviously, but the soil cohesion would not. Furthermore, the influence of the water level change which is caused by tide on the face stability was studied. The results showed that the change of water table leads to the redistribution of pore water pressure around the tunnel face and results in the fluctuation of the limit support pressure.