Experimental investigation of failure mechanisms of granites with prefabricated cracks induced by cyclic-impact disturbances

Engineering rock mass is normally subject to cyclic−dynamic disturbances from excavation, blasting, drilling, and earthquakes. Natural fractures in rock masses can be reactivated and propagated under dynamic and static loadings, which affects the stability of rock mass engineering. However, fractured rock mass failure induced by cyclic-impact disturbances is far from clear, especially considering varying angles between the rock mass and the direction of impact loadings. This work investigated rock deformation and failure characteristics through cyclic impact tests on granite samples with cracks of different angles. A Hopkinson bar was employed for uniaxial cyclic impact tests on granite samples with the crack inclination angles of 0−90°. The magnetic resonance imaging technique was used to determine rocks’ porosity after cyclic impacts. The stress−strain curves, porosity, strength, deformation modulus, failure modes, and energy density of samples were obtained and discussed. Results showed that the crack inclination angles significantly affected the damage evolution and crack morphology of rocks. Under the constant cyclic impact, the dynamic deformation modulus and dynamic strength of rock samples first increased and then decreased with the increase in crack inclination angle. The failures of granite samples for inclination angles of 0 and 90° were dominated by tensile cracking, while those for the inclination angles of 30−60° were dominated by shear cracking. The energy density per unit time gradually decreased with the increase in impact cycles. The results can provide references for the stability analysis and cyclic-impact-induced failure prediction of fractured rock masses.