Research on the Relationship between Shear Mechanical Characteristics of Rough Joints and Shear Displacement under Cyclic Loading Conditions

To investigate the mechanical behavior of rough joint surfaces under cyclic shear, shear tests were conducted using the bi-directional dynamic cyclic shear test system to study the evolution of shear stress, normal displacement, and dilation angle of rough joint surfaces under different shear displacements. The results show that: (1) The peak negative shear stress after positive shear gradually decreases with an increase in shear displacement, and the negative peak strength decreases from 4.13 MPa to 2.94 MPa; (2) The shear stiffness continuously decreases and tends to stabilize with an increase in tangential displacement. The average shear stiffness of positive shear decreases from 473.69 MPa/m to 21.37 MPa/m, and the average shear stiffness of negative shear decreases from 413.82 MPa/m to 8.95 MPa/m; (3) When the shear displacement is small, the normal displacement tends to reach a stable value with an increasing number of cycles. When the shear displacement is large, the normal displacement decreases continuously with an increasing number of cycles, but the changes in shear stress, shear dilation angle, and other parameters have already stabilized. This indicates that the influence of wear within a certain range on the mechanical properties of the joint surface is limited.; (4) The change in shear dilation angle is related to the morphology of joint surfaces. It decreases continuously with an increase in cyclic times and finally tends to stabilize.