Numerical simulation research on excavation face stability of different depths of shield tunnel

By comparing with physical model tests, two-dimensional particle flow code (PFC^2D) was used for numerical simulation of the tunnel excavation process to analyze soil failure mechanism under various buried depths and densities. First, the variations of the support force and the surface subsidence were studied and the results of model tests and numerical simulation were comparatively analyzed. Then, the limit support force was determined. Finally, the failure mechanism of the soil in front of the excavation face was further understood by utilizing PFC^2D to study the soil arch effect. The results show that the changes of the supporting force and the ground settlement can be divided into two stages, and are not affected by the buried depth; the soil arching continues to be developed after the local failure, leading to the overall instability; when the depth is smaller, the soil arching fails to be formed, otherwise, the sliding zone and the soil arching region enlarge with the increase of the buried depth. The consistency of results of numerical simulation and physical test verifies the feasibility of particle flow simulation with longitudinal surface. Therefore, PFC^2D can be used in depth for particle flow simulation.