Experimental study of deformation behavior of rock joints under cyclic shear loading

Using cement-mortar as similar material, joint specimen with three joint wall strengths and five asperity angles are prepared. Then a series of cyclic shear tests are performed at four normal stresses on the cyclic shear test apparatus. Based on the test results and loading characteristics, the dilation angle and shear stiffness are defined. The normal deformation of joints under cyclic shear is characterized by dilation angle, and the tangential deformation is characterized by shear stiffness. Based on a variety of cyclic shear test results, the relationships between dilation angle and shear stiffness with shear cycles are analyzed. By comparing the results of different experimental conditions, the effects of initial asperity angles, joint wall strength and normal stress on the joint deformation properties are also analyzed. Research discovers that, the dilation angle and shear stiffness all appear a first quick back slow downward trend with the increase of cycle number. For the joint specimens with low and medium asperity angles, downward trend for dilation angle and shear stiffness shows an accelerating tendency with the increase of initial asperity angles and normal stress; but show a decelerating tendency with the increase of joint wall strengths. For the joint specimens with higher asperity angles, the downward trend for dilation angle and shear stiffness keep mainly unchanged.