Analysis of Large-section Tunnels with Small Spacing in Elastoplastic Stress-seepage-damage Model

Small spacing tunnels has the characteristics of large-section, lower flat-ratio and poor surrounding rock stability and its stability is significantly influenced by seepage field. The coupling effect of stress-seepage-damage on surrounding rock is obviously. According to this, the FEM calculation program based on elastoplastic stress-seepage-damage model of rock is established. Back analysis program is compiled on the basis of the principle of differential evolution algorithm in order to solve the problem that elastoplastic damage model involves many parameters and not so easy to determine. The calculating program is used to calculate the stability of Da-Dongshan tunnel which has large-section with small spacing. The parameters are identified by using back analysis program based on the displacement date from field monitoring. The stress distribution and seepage filed of the supporting structure are analyzed. The results show that the stability of surrounding rock is influenced by groundwater seepage which would increase the damage zone.