Macro–Microscopic Study on the Shear Characteristics of Filled Joints with Different Roughnesses

Rock-like materials and Barton’s standard joint curve were used to make filled joint specimens, and the shear characteristics of the filled joints were studied. Discrete element software was used to analyze the failure mechanism during filled joint shearing. Based on the experimental findings, a new theoretical model of joint shear strength was proposed. It was found that joint roughness has a great effect on filled joint shear failure, which is manifested via three different morphologies. The effects of the filler on the shear stress–strain curve are mainly a higher slope in the elastic phase and a lower slope in the plastic phase. The shear failure of the filled joint starts from local small damage of the filling and then progresses to failure of the bonding surface or the filling itself. Based on the proportion of the joint failure surface area to the joint surface area, a new formula for calculating shear strength is proposed.