Abstract: The Shanghai metro line 12 crosses the Tiantong road and Zhapu road foundation pit groups. The deformation characteristics of the metro tunnels are complex due to the superposed effects caused by excavation of foundation pits on both sides of the tunnel. Sub-pit excavation method is adopted to reduce the excavation size of the foundation pit, thus the deformation of the tunnel can be effectively controlled. However, different sub-pit excavation schemes might cause different effects on the metro tunnels. Three-dimensional finite element analyses are carried out based on the small strain soil constitutive model and considering the interaction between soils and structures. Gradual deformation and superposed effects on the adjacent metro tunnels caused by excavation are revealed. It is beneficial to control the horizontal deformation of tunnels when synchronously excavating the foundation pits on both sides, but the vertical displacement of tunnel exhibits larger settlement due to superposed effect. In general, the excavation of the foundation pit causes both vertical compression and horizontal tensile deformation of the tunnels. However, the convergence deformation of the tunnel is not significant, showing that the tunnel is still in safe state.

Key words: excavation group, metro tunnel, superposed effects, deformation characteristics, three-dimensional finite element