New insights into the dynamic mechanical behavior and fracture mechanisms of randomly jointed rock under impact loading

Abstract The extensively developed joint structures in natural rock masses exert a profound influence on their dynamic response and failure behavior under impact loading. In particular, the structural complexity of random joint networks poses a potential threat to the stability of rock engineering. To elucidate the mechanical response and crack evolution behavior of randomly jointed rock masses subjected to impact loading, this study conducts a systematic investigation by integrating laboratory experiments with numerical simulations. Randomly jointed specimens with varying joint numbers and lengths were prepared using a cement-casting method. The Split Hopkinson Pressure Bar (SHPB) system was employed to obtain stress–strain curves, energy distribution characteristics, and fragment size distributions. Furthermore, an innovative joint-modeling procedure was developed to construct a three-dimensional finite element model consistent with the laboratory specimens, enabling detailed exploration of the effects of joint geometry on stress propagation and damage evolution. The results indicate that joint geometry exerts a significant influence on the peak strength, peak strain, and energy transmission pathways of the rock, with the maximum peak strength decreasing by approximately 36%. The average fragment size decreases from 21.32 mm to 14.45 mm with increasing joint number, and from 23.38 mm to 10.12 mm as joint length increases. Meanwhile, the failure mode transitions progressively from tension-dominated cracking to shear-dominated coplanar fracture propagation. The findings of this study provide valuable insights for dynamic disaster prevention and engineering design in jointed rock masses.