Experimental and Numerical Studies on Dynamic Response and Fracture Characteristic of Sandstone with Multiple Defects

Abstract Geological discontinuities (e.g., cracks, joints, faults, and cavities) fundamentally alter the integrity and mechanical behavior of rock masses. Under dynamic loading, such discontinuities induce stress concentration, disturb stress-wave propagation, and govern crack evolution, thereby acting as critical triggers for dynamic hazards in underground engineering. This study systematically investigates the dynamic response of sandstone containing multiple interacting defects, including intact, hole, flaw, intersected hole–flaw, and independent hole–flaw configurations. A combined experimental–numerical approach is employed, integrating triaxial Hopkinson bar (Tri-HB) expriment with quantitatively validated continuum-discrete coupling simulation. The results show that distinct dynamic stress–strain responses and fracture characteristics are governed by multiple interacting defects. Holes predominantly induce radial cracks and arching effects, while flaw tips cause strong directional stress concentration, with the inclination angle controlling crack propagation and seismic isolation. Hole–flaw intersected structures significantly accelerate crack coalescence, whereas hole–flaw independent structures exhibit pronounced energy dissipation and seismic isolation. At the mesoscale, failure evolution follows a sequence: shear triggering, tensile propagation, global instability. Force chain disturbance governs crack initiation direction, and local vortex-like velocity fields emerge near discontinuity intersections, promoting crack connectivity and dynamic instability. Energy partitioning analysis demonstrates that linear strain energy remains the dominant storage pathway, while complex discontinuities weaken storage capacity and markedly enhance frictional sliding, damping dissipation, and fragment motion, thereby enhancing energy dissipation and reducing energy storage capacity. These findings offer theoretical insights into the dynamic failure mechanisms of rock masses containing multiple discontinuities and guidance for hazard prevention in underground engineering.