Failure Mechanisms and Energy Evolution of Jointed Rock-Like Materials under Triaxial Compression: Experimental and Numerical Simulation Study

Joint properties strongly influence the mechanical behavior of jointed rock masses. To clarify the influence mechanism under triaxial conditions, triaxial compression tests were performed on rock-like jointed specimens with different joint roughnesses and dip angles under various confining pressures. Mechanical properties and failure mechanisms were examined via mechanical parameters, energy analysis, mesoscopic damage evolution, and mechanical modeling by combining laboratory experiments, numerical simulations, and theoretical analysis. Results show three dominant failure modes: Matrix Failure, Combination Failure, and Joint Shear Failure, among which the dip angle produces decisive anisotropy. As joint roughness increased from 5 to 15, the extreme value of the anisotropy index decreased from 74% to 58%. From an energy perspective, joint-surface characteristics significantly affected key energy components, including elastic energy and dissipated energy, and a critical energy value of 4.2 was proposed to distinguish the brittleness–ductility transition. Using particle flow code, the failure evolution of jointed specimens was further explored at the mesoscale, revealing damage initiation, crack propagation, and progressive failure. Finally, a jointed rock model incorporating joint roughness and dip angle was established to interpret and explain the observed failure mechanisms.