Dynamic mechanical behaviors of single-jointed rock mass under cyclic impact loadings

In practical engineering, rock frequently suffers from recurrent dynamic disturbances, posing serious threats to engineering safety. To investigate the dynamic mechanical behavior of jointed rock under cyclic dynamic disturbances, cyclic impact tests of single-jointed gabbro (SJG) were conducted using a split Hopkinson pressure bar (SHPB) test system. The stress equilibrium during the tests was verified using the three-wave method and the force balance coefficient method. The dynamic mechanical behavior of the specimens was comprehensively analyzed in terms of impact resistance, stress-strain relationships, energy and damage evolution, as well as dynamic failure mechanisms. The results show that single-jointed rock specimens can achieve stress equilibrium under cyclic impact conditions. The failure mode of the specimens under cyclic impacts is splitting, and the joint inclination angle significantly influences the impact resistance of the specimens. As the joint inclination angle increases, the impact resistance of the specimens also increases. During the cyclic impact process, strain rebound occurs in all specimens, and their mechanical properties do not monotonically degrade with an increasing number of impacts. The peak stress of the specimens generally exhibits a decreasing trend with the number of impacts. The cumulative damage coefficient, represented by dissipated energy, increases approximately linearly with the number of impacts, while the increase rate decreases with larger joint inclination angles. Under low-stress impact loading, the compressive-shear stress within single-jointed specimens is insufficient to generate shear cracks. The failure of specimens primarily results from the progressive propagation of tensile cracks induced by tensile stress, which eventually coalesce with the joint. The failure mechanism of multi-jointed rock masses resembles that of single-jointed rock masses. During cyclic impact loading, both compaction of micro-defects and initiation of micro-cracks at joints occur simultaneously. However, the impact resistance of multi-jointed specimens depends on whether the cracks can interconnect the joints. For intact rock specimens, the failure process initially involves compaction of micro-defects, followed by probabilistic activation of micro-cracks, ultimately leading to specimen failure.