Investigation on seepage evolution property of surrounding rock under the tunneling and water surge

The tunnel water surge seriously threatens the tunneling safety. Based on COMSOL numerical simulation, the tunneling model is established and the tunneling stress evolution law is studied. Based on the tunneling stress variation law, the water seepage test of tunnel surrounding rock is designed and carried out. It is studied that tunneling stress can be divided into the area of in-situ stress, supporting effect and stress stabilization. Moreover, the tunneling stress increases sharply in the supporting effect area. In the mechanical loading early stage of seepage test, that is, the in-situ stress area, the rock deformation and permeability are relatively stable. The post-peak failure stages are divided into passive and active unloading stages of σ1-σ3. In the σ1-σ3 passive unloading stage, that is, the supporting effect area, the strain and permeability increase dramatically. It reflects the crack propagation and water surge process of tunnel surrounding rock. In the σ1-σ3 active unloading stage, that is, in the stress stabilization area, the permeability first slows down and then rapidly decreases. It reflects the tunnel water surge weakening under the lining support action. Meanwhile, based on the rock porosity and statistical damage variables, the permeability evolution model is established. By comparation, the model calculated results are consistent to the seepage test data, which verifies the model validity. The permeability mathematical model can serve as a reference for the prediction of tunnel water surge node.