Mechanical behavior and subsequent seepage characteristics of rough structural planes in sandstone under constant shear rate

To investigate the dynamic shear mechanical response and post-damage permeability characteristics of rough structural planes, a dynamic shear system was utilized to conduct shear tests on rough structural planes of sandstone under varying shear rate conditions. The effects of shear rate and roughness coefficient on peak shear strength and slip behaviors were analyzed. After the shear test, the influence of dynamic shear on the damage characteristics of rough structural surfaces was analyzed using three-dimensional scanning technology. Subsequently, seepage tests were conducted on damaged structural surfaces under different confining pressures to further investigate the subsequent seepage characteristics of damaged structural surfaces after dynamic shearing. The results of dynamic shear tests show that the dynamic peak shear strength of sandstone structural planes exhibits a decreasing trend with the shear rate, and shear rate influence on shear stiffness is insignificant. As the shear rate increases from 50 mm/s to 210 mm/s, the peak shear strength of structural planes with joint roughness coefficient of 12.43 declines from 8.49 MPa to 6.88 MPa. In addition, the dynamic peak shear strength of structural planes increases with the roughness under the same shear rate condition. The frequency of height distribution of damaged structural planes decreases with the shear rate. Under the same roughness condition, the damage degree of the structural plane generally increases with the shear rate, resulting in a decline in crack opening and thus affecting the permeability properties of the structural plane. The flow test results indicate that the relationship between the hydraulic gradient and the volumetric flow rate of the damaged structural plane adheres to Forchheimer’s law. In addition, the transmissivity of the damaged structural plane decreases with the shear rate under the same confining pressure condition, while increasing with the joint roughness coefficient.