Characteristic stress response law and fracture precursor of granite under different dynamic disturbance damage conditions

Based on a series of cyclic impact and uniaxial compression tests, this study investigates the effects of prior dynamic damage on the mechanical behavior of granite specimens and their damage precursor characteristics. The results indicate that the primary wave (P-wave) velocity of granite specimens decreases as the number of cyclic impacts increases, while their internal damage variable gradually increases. Additionally, as the number of cyclic impacts rises, the ratio of crack closure stress to strength increases, while the ratio of crack initiation stress to strength and the ratio of damage stress to strength decrease for granite specimens. In order to investigate the evolution process of microcracks in different stress stages of granite specimens under different damage conditions, the acoustic emission (AE) event rate of granite specimens during deformation and failure under different dynamic damage states was statistically analyzed. Moreover, the main-frequency of AE signals from granite specimens during deformation and damage exhibits clear fractal characteristics over time. When the main-frequency fractal dimension of the AE signal before peak damage decreases to a minimum value, it is considered to be a precursor feature of critical damage of granite specimens in different damage states. These research findings offer a theoretical foundation for evaluating stability and designing support systems for tunnel surrounding rock under the influence of multiple blasting events.