Study on the evolution of limestone damage and permeability under the tunnel driving stress path

The tunnel water inrush problems threaten the safety of tunneling. To understand the water inrush mechanism in tunnel tunneling, triaxial water seepage test and COMSOL numerical simulation were applied to study the water seepage law of tunnel surrounding rock according to the tunnel driving stress path. The results show that the permeability changes slowly, increases sharply and decreases sharply, respectively, during seepage and mechanical loading-unloading. However, during the (sigma 1 - sigma 3) active unloading stage, the permeability cannot return to the state before the plastic stage. The permeability presents a highly fitting exponential relationship with the stress of deviatoric and effective volume. During different loading and unloading stages, the index relationship is different, which is related to the rock damage degree. Through uniaxial cyclic loading-unloading acoustic emission test, it is verified that axial strain epsilon 1 is related to cumulative AE count, that is rock damage degree. The damage variable D based on axial strain epsilon 1 was established, and the permeability evolution law was effectively characterized by damage variable D. The permeability and crack evolution process cannot be directly observed during seepage test. The numerical model of real heterogeneous rock samples is established based on COMSOL. The simulated rock shear fracture feature is close to that of laboratory tests. In the numerical simulation of seepage, the evolution laws of damage, fracture and permeability in rock are effectively quantified. It is proved that the necessary numerical simulation can serve as an effective supplement to the laboratory test.