Roughness-filling interaction controlling shear behavior and failure mechanisms of gypsum-filled rock joints

Direct shear tests were conducted on gypsum-filled joints to investigate the effects of filling thickness, JRC, and gypsum-to-water ratio on shear responses and failure mechanisms. The results show that increasing filling thickness decreases peak shear strength, residual strength, and normal dilation, with a more pronounced weakening effect for rougher joints.

Conversely, increasing JRC enhances shear performance, but this strengthening effect is progressively reduced by thicker filling layers. The gypsum-to-water ratio does not alter the overall influence trends of filling thickness and roughness, but it regulates the compactness and fragmentation characteristics of the infill medium, with higher ratios improving roughness-induced strengthening and reducing infill crushing.