Experimental and numerical modeling study of rock joint mechanical properties and failure mechanisms under cyclic shear

Abstract

Cyclic loading is a common concept in geotechnical engineering, which has an important effect on rock joints. To study the mechanical properties and failure mechanisms of rock joints under cyclic loading, a kind of rock joint cyclic shear device with a top-to-top configuration is proposed in this work. Cyclic shear tests of rock joints are carried out with the cyclic shear equipment. With three–dimensional texture scanning technology, the cyclic shear failure mode of the rock joint is analyzed. The variation trends of shear strength and stiffness of the rock joint under the combined action of normal stress, joint roughness, shear rate, and cyclic shear number are studied. The results show that the normal stress and the roughness are positively related to the cyclic shear strength of the rock joint. With the increase of shear rate and number of cycles, the shear strength and stiffness of the rock joints decrease gradually. In the first cycle of the shear process, the peak shear strength and stiffness of the rock joints reach the maximum values. After the second cycle, the peak shear strength and stiffness of the rock joints decrease slightly and tend toward a constant value under the same normal stress. Observation of the sheared rock joint surface reveals that sliding and shearing damage to the protrusions occurred during the cyclic shear process. Under the combined action of the normal stress, joint roughness, shear rate, and cyclic shear number, the protrusions would slide while moving up to a different height until they are eventually sheared off. In the next cyclic shear process, the friction and shear damage of the residual protrusions continues to occur. With the increase of the number of cyclic shear processes, the wear on the residual protrusions gradually decreases and stabilizes. Finally, the numerical cyclic shear test of the rock joint is performed with the discrete element method (DEM) code 3DEC. A good comparison is found between laboratory data and DEM results.