Comparative 2D and 3D peridynamic modeling of frictional failure in jointed rocks with a unified interface-orientation identification method

The frictional behavior along rock joints is a fundamental mechanism governing slope stability and failure. In 3D engineering applications, accurate modeling of this behavior requires a computationally efficient determination of interface orientations. This study introduces a unified orientation-based method, derived from the divergence theorem, to compute unit normal and tangential vectors on arbitrarily shaped interfaces in both 2D and 3D within a meshfree formulation. Integrated into a peridynamic frictional contact model, the method is verified against the Hertzian solution under normal loading and validated through laboratory shear tests on rock joints with varied surface geometries. Applied to a 3D jointed rock slope, the model reproduces a progressive failure sequence that initiates at the joint tip and propagates toward the crest, successively involving frictional degradation, intact-block disintegration, tensile-cracking transition, and crest compaction. Comparative 2D and 3D contact analyses reveal that out-of-plane geometric variations, with the associated kinematic constraints, govern stress localization and damage evolution in 3D, thereby highlighting the limitations of 2D approximations.