Exploring Effect of Microproperties on Shear Strength of Rock Joints through Physical and Numerical Modeling

Understanding the shear strength and failure mechanism of a rock joint is essential in rock engineering. This study performed a series of direct shear tests and discrete element modelings on artificial joint specimens to investigate the effect of roughness [randomly generated joint profiles with joint roughness coefficient (JRC) = 20, 19.6, and 10] on the joint strength. The results of the numerical simulation were consistent in the peak shear strength with the laboratory tests and Barton's equation. From a microscopic viewpoint, the rock joint's peak and residual shear strength were mainly mobilized from the friction property of such a joint profile. The contribution of friction to the shear strength at the residual stage was reduced because of dilation behavior and decreasing contact area along the joint surface. Therefore, the mobilized friction angle decreased from the initial basic friction angle to a certain value depending on the initial JRC value. The mobilized JRC of a rock joint was found to be related to the initial JRC, the unconfined compressive strength (UCS) of joint material, and the applying normal stress. The surface of joint models with high UCS is less damaged than that with low UCS. Finally, a new model for predicting the residual shear strength of a rock joint was also proposed, which can be applied for the joint using both randomly generated profiles and Barton's standard profiles.