Damage evolution of rock joints under high-strain-rate cyclic shearing based on morphological characterization

The high-strain-rate cyclic shear behavior of rock joints under seismic loading strongly influences the dynamic stability of slopes. To investigate this behavior, high-strain-rate cyclic direct shear tests were conducted on reproducibly prepared two-dimensional (2-D) and three-dimensional (3-D) rock joints under normal stresses of 0.5–2.0 MPa. Three-dimensional topographic scanning was used to relate surface degradation to the evolution of shear strength, dilatancy, and stiffness. The results show that mechanical degradation is concentrated in the initial cycles. Higher normal stress increases the initial shear strength and stiffness, but also intensifies asperity damage and accelerates subsequent deterioration. After approximately five cycles, the peak shear strength decreases to 10%–60% of its initial value. The shear stiffness exhibits a typical two-stage degradation pattern, decreasing by 50%–70% after the first cycle and gradually stabilizing after approximately five cycles. Greater roughness enhances the initial shear resistance through asperity interlocking but is also associated with greater damage accumulation. The 2-D joints exhibit directional wear along a relatively fixed shear path, whereas the 3-D joints show more heterogeneous contact evolution and nonlinear degradation. These findings improve understanding of the cyclic degradation of rock joints and provide experimental evidence for seismic stability assessment of jointed rock slopes.