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.

The effect of confining pressure on the hydraulic conductivity of capillaries in cylindrical samples is examined. The three-dimensional-printed samples were made from photopolymer resin. Capillaries in the samples were modeled by grooves of various geometric shapes. The mechanism of capillary deformation in the samples under increasing confining pressure has been identified. The change in capillary conductivity depending on their location (central and lateral) and configuration (sinuous) has been revealed. Based on correction functions for the geometric dimensions of the capillaries, it has been mathematically confirmed that under confining pressure, a capillary deforms primarily along the contact plane due to the sliding of the sample’s halves against each other. The width of a capillary is more sensitive to confining pressure than its depth. It has been established that the exponent in the conductivity (permeability) equation of the samples under cyclic loading is determined by the hydraulic area of the capillary. The obtained values of the width and depth correction factors allow for predicting changes in the filtration resistances of capillaries in various materials. Capillary deformation manifests as a change in its geometric dimensions (height and width), i.e., the crushing of the capillary banks is observed, leading to a reduction in the capillary’s hydraulic area, which causes a decrease in sample conductivity with an incomplete hysteresis.