Deformation and stability analysis of rectangular tunnel in soft rock ground using a strain softening type elasto-plastic model

The purpose of this study is to investigate the deformation and stability of rectangular tunnel excavated in the soft rock ground. In order to simulate the excavation of a rectangular tunnel below the underground water level, a series of the soil-water coupled finite element analyses using a strain softening type elasto-plastic constitutive model is carried out. The generally expected negative excess pore water pressure hardly occurs around the rectangular tunnel in the given soft rock ground due to the unloading by the excavation. The unstable behavior caused by the dissipation of the negative pore water pressure cannot be observed. Furthermore, it can be confirmed that the additional settlement of ground surface due to the drainage does not occur.