Characterizing the dynamic behavior and progressive damage evolution of carbonaceous slate under cyclic impact loading

Drilling and blasting tunneling is a cyclic process in which tunnel rock undergoes repeated blast loading, affecting its dynamic characteristics, energy evolution, and damage progression. To explore the dynamic mechanical properties and damage mechanisms of carbonaceous slate under cyclic impact loads of varying intensities, cyclic dynamic tests are conducted using a triaxial split Hopkinson pressure bar. This study analyzes the stress-strain relationship, energy damage evolution, and macro-to-micro failure characteristics. The results show that peak stress and strain are significantly influenced by impact intensity and the number of impacts. The initial dynamic stress is positively correlated with the impact intensity, but with more impact, the dynamic stress decreases while the peak strain increases. Energy evolution follows a pattern of "slow growth−fluctuating growth−rapid growth," with the crack initiation stress and its proportion decreasing. CT and SEM analyses reveal that as the impact intensity increases, failure becomes more chaotic, the fracture volume increases, and the fracture mode shifts from interlayer and intergranular to through-layer and trans-granular fractures. These findings provide an experimental basis for soft rock tunnel stability analysis.