Study on the dynamic characteristics of rock discontinuities under high cyclic shear rate

The natural occurrence of numerous discontinuities in rock masses makes them prone to significant displacements and friction degradation under external dynamic forces，thereby increasing the risk of instability. To investigate the mechanical properties of jointed rock masses under cyclic dynamic conditions，this study focuses on natural red sandstone and explores the shear mechanical characteristics of rock discontinuities under cyclic shearing，with a specific emphasis on the dynamic properties of rock masses by setting a high shear rate. The evolution of shear stress and normal displacement during cyclic shearing is analyzed，and a peak shear strength prediction model for structural planes is established，incorporating the number of cyclic shear cycles based on plastic work theory. The results show that：(1) The applied cyclic shear rate (2 mm/s) reaches the dynamic range，and in comparison to quasi-static direct shear tests，this rate more accurately simulates the shear mechanical behavior of discontinuities under dynamic conditions. (2) During cyclic shearing，the number of cycles，type of discontinuities，and normal stress significantly influence the evolution of shear stress on the discontinuities. Normal displacement exhibits distinct patterns at shear displacements of 0 mm and ±5 mm. As the number of cycles increases，normal displacement gradually decreases，indicating a reduction in dilatancy and an increase in compaction. (3) A peak shear strength prediction model that accounts for the number of cyclic shear cycles is established，with an overall error of approximately 10% compared to actual conditions，demonstrating good applicability. The research findings provide theoretical support for the safety and stability assessment of rock engineering under dynamic disturbances.