Shear response and spatial evolution of roughness degradation in rock fracture surfaces with heterogeneously distributed multi-angle asperities

The simplified characterization of rough rock fracture morphology is fundamental to understanding shear mechanical behavior. This study presents a method for constructing fracture surfaces by integrating profiles with varied inclined dentate asperities. The resulting five surfaces (D_1 to D_5) were quantitatively validated using the roughness index θ * _max /(C+1) , demonstrating distinct roughness gradients. Utilizing three-dimensional (3D) printing technology, these fracture types were cast into mortar specimens for direct shear testing under varying normal loads. Experimental results allowed for a detailed analysis of shear stress, normal displacement, and their correlation with initial roughness and normal stress. Post-test 3D scanning revealed significant spatial variations in macroscopic surface damage. Investigation into the reduction and residual values of surface roughness indicates that degradation is closely linked to initial topography. Specifically, the roughest regions sustain the most significant damage and contribute most substantially to shear resistance. This research offers a feasible and novel approach to evaluating the mechanical properties of rock fractures.