Shear behaviors of intermittent joints subjected to shearing cycles under constant normal stiffness conditions: Effects of loading parameters

A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading. The results show that the loading parameters (initial normal stress, normal stiffness, and shear velocity) determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle, creating different morphologies of macroscopic step-path rupture surfaces and asperities on them. The differences in stress state and rupture surface induce different cyclic shear responses. It shows that high initial normal stress accelerates asperity degradation, raises shear resistance, and promotes compression of intermittent joints. In addition, high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints. High shear velocity results in a higher shear resistance, greater dilation, and greater compression. Finally, shear strength is most sensitive to initial normal stress, followed by shear velocity and normal stiffness. Moreover, average dilation angle is most sensitive to initial normal stress, followed by normal stiffness and shear velocity. During the shear cycles, frictional coefficient is affected by asperity degradation, backfilling of rock debris, and frictional area, exhibiting a non-monotonic behavior.