Numerical Analysis of Mechanical Behavior of a Tunnel in Swelling Volcanic Rocks

In this study, we propose an elasto-plastic-damage model to analyze mechanical behavior of a tunnel constructed in swelling volcanic rock mass. The elasto-plastic part of this model is based on the Modified Cam Clay (MCC) model, which can express the softening and hardening behavior of ground materials. The stiffness deterioration due to the damage that occurs with the process of water absorption is also taken into consideration. Furthermore, we formulate an implicit stress update algorithm (return mapping algorithm) to improve the computational accuracy and robustness of the computation for the model when it is implemented in finite element method (FEM). Several numerical simulations were conducted for a tunnel in swelling rocks called Sakazukiyama Tunnel, which is belong to Yamagata Expressway, to analyze mechanical behavior, containing the swelling displacement and damage progress with the process of swelling. The computation results show that stress increased remarkably as swelling happened; and the uplift of tunnel invert is larger when the damage due to the swelling of bedrock is considered, and that the simulation results with consideration of damage exhibit better approximation of the deformed state of Sakazukiyama Tunnel.