Dynamic damage characteristics of shallow-buried rock mass under cyclic impact

To elucidate how cyclic blasting load parameters affect the mechanical properties of differentiated granite surrounding rock in tunnel construction, this study conducted dynamic impact tests on slightly weathered granite samples at varying impact velocities and cycles. Post-impact damage, these granite samples were subjected to mercury injection pore method tests and longitudinal wave velocity tests. The findings indicate that granite specimens exhibit a strain rate effect under impact loading, with dynamic peak strength and peak strain escalating as impact velocity rises. Under cyclic impact loading, the dynamic peak strength of the samples progressively diminishes, while maximum strain ascends. At a constant impact velocity, with incident energy held steady, transmitted energy declines over successive impacts, whereas reflection and absorption energies trend upward. Similarly, at a constant impact velocity, longitudinal wave velocity decreases as the number of cyclic impacts increases, signifying that sample damage intensifies with more cyclic impacts, a conclusion corroborated by the rising trend of internal pores within the samples. These research conclusions offer a more scientific theoretical foundation for the parameter design of the drilling and blasting method for shallow-buried, large-span, thin-rock roof stations, thereby enhancing construction safety.