DEM analysis of the shear properties for rock fractures with identical roughness index under CNS conditions

Surface morphology significantly influences the shear properties of natural rock fractures under the constant normal stiffness (CNS) boundary conditions, typically quantified using various roughness indexes. Currently, it has not been verified whether rock fractures with the identical roughness index necessarily have the same shear characteristics, introducing uncertainty in rock mass engineering practice. To address this issue, this study first introduces several fracture profiles having identical roughness index o* max/(C+1) but differing geometries. Subsequently, numerical fracture specimens with identical roughness index were established by Discrete Element Method (DEM), and CNS shear tests were carried out considering varying roughness grades and normal stiffness (Kn). The test results were analyzed to explore the differences in shear mechanical characteristics of rock fractures having the identical roughness index, such as stress, deformation and failure. Additionally, the stress features of local asperities on fractures were examined to elucidate the role of roughness in resisting external loads. It was found that local asperity distribution is an important factor contributing to the discrete shear behavior of rough rock fractures, recommending its inclusion in roughness evaluation methods.