Damage-Seepage Evolution Mechanism of Fractured Rock Masses Considering the Influence of Lateral Stress on Fracture Deformation Under Loading and Unloading Process

Fractures serve as the main pathways for the occurrence and transportation of gases within rock layers. Studying the seepage characteristics of fractured rock masses during loading and unloading processes is an essential issue for understanding the mechanism of hazardous gas migration in surrounding rock under tunnel excavation action. Experiments on rock mass seepage under different precast fracture angles and confining pressures during the loading and unloading process were conducted by using a multi-field coupled triaxial testing system. The findings of the tests indicate that the lateral stress, particularly during the unloading stage, induces the volumetric expansion of fracture. However, the influence of the fracture angle on rock mass fracture expansion is greater than that of the confining pressure. Moreover, the effect of the lateral stress on the fracture surface increases the permeability of the rock mass, nevertheless, the permeability decreases with increasing the confining pressure and decreasing the fracture angle. Under the same stress level value, during the loading stage, the permeability of the rock mass linearly decreases with increasing the confining pressure, while during the unloading stage, the permeability of the rock mass decreases nonlinearly with increasing the confining pressure. Based on the test results, a fluid-solid-damage coupling computational model for the fractured rock mass's permeability was established by considering the influence of the lateral stress on the fracture surface. In addition, further analysis related to the evolution process of the damage and the rock mass seepage has been done. The result reveals that the change in chi with increasing confining pressure exhibits logarithmic characteristics. As the fracture angle decreases, the respective variation ranges of chi are: 0.005 similar to 0.03, 016 similar to 0.17, 0.2 similar to 0.22.