DEM-Based Investigation of Joint Effects on Projectile Penetration in Rock Mass

Abstract Understanding the dynamic interaction between high-velocity projectiles and jointed rock masses is essential for assessing impact resistance in geotechnical, mining, and defense engineering. This study employs a three-dimensional discrete element method (DEM) to investigate projectile penetration into jointed and intact rock analogs, with model calibration verified against published experimental results. A comprehensive parametric analysis was performed to examine the influence of joint orientation, spacing, stiffness, and projectile velocity on penetration response. The evolution of displacement and damage patterns revealed that joints with low loading angles promote deep, shear-dominated deformation zones, whereas joints with high loading angles constrain motion and enhance lateral energy dispersion. A new parameter, the critical loading angle, was identified to characterize the transition from joint-dominated to matrix-dominated penetration behavior. The critical angle decreases with increasing velocity, converging to approximately 35°–40°, indicating a velocity-dependent shift in governing failure mechanisms. In addition, joint stiffness was shown to significantly affect penetration resistance, with more compliant joints facilitating deeper penetration due to enhanced interfacial deformation. Comparison with existing empirical formulations demonstrates that joint orientation introduces anisotropic effects overlooked by conventional rock quality classifications. This study advances the mechanistic understanding of impact behavior in jointed rock masses and provides essential insights for the design of protective barriers and underground structures in fractured rock masses.