Experimental and numerical investigations on nonlinear shear behavior of rough joints

Shear behavior of rough rock joints is considerably complex, as the failure process is governed by non-uniform degradation of asperities. To investigate the nonlinear shear behavior of rough joints, a series of experimental and numerical tests were conducted on saw-toothed mortar joints. It was found that nonlinear shear behavior of joints with regular asperities is mainly relevant to shear failure of asperities. There are three types of failure mechanisms: (a) surface wearing, (b) tensile splitting and (c) shearing off. In contrast, for joints with irregular asperities, shear nonlinearity is attributed to the failure of asperities as well as the transfer of load. In numerical simulations, this load transfer is clear and continuous. Before the shear strength is reached, stress gradually concentrates in the steepest asperities. After that, it transfers from the steeper asperity back to gentler ones. Based on the results of experimental and numerical tests, an estimation method for shear displacement at yielding strength of rough joints was proposed and verified. Our findings could provide insights into the shear stiffness evolution during shearing and facilitate better understanding on shear mechanisms of rough joints.