Deformation and seepage characteristics of precast fractured rock mass considering the influence of axial stress

Hazardous gas migration in rock strata primarily occurs through fractured media, with the stress state of the rock mass significantly influencing its permeability. Generally, natural rock masses are in a triaxial state of unequal principal stresses. Studying rock mass deformation and seepage under various stress states is crucial for accurately predicting gas migration in rock strata. The deformation and permeability of rock mass under fluid-solid coupling were studied by triaxial test system considering different fracture angles and confining pressures. The results show that: (1) The precast fracture strain of rock mass initially decreases and then increases with the increase of axial stress. At confining pressures below 25 MPa, axial stress primarily causes volumetric expansion of the fracture, whereas at pressures above 25 MPa, it primarily leads to volumetric shrinkage. (2) Volumetric expansion of rock masses is primarily due to precast fractures at low confining pressures, and to newly formed fractures at high pressures. The change of rock permeability during compression of precast fractured rock mass is mainly determined by the deformation of precast fracture. (3) When the fracture angle is 90 degrees, 80 degrees, and 70 degrees, the rock mass permeability at peak stress increases by 4% to -0.7%, 0.5% to -6.3%, and -0.2% to -15% compared with the initial stress, respectively, with the increase of confining pressure. The influence of the fracture angle on the permeability of rock mass under axial load is slightly higher than that confining pressure. (4) Considering the influence of different stress levels on fracture deformation, a calculation model for fracture permeability under triaxial state was established. It was found that the sensitivity of the lateral stress influence coefficient on normal deformation chi decreased with the increase of confining pressure and fracture angle.