Peak impact stress and porosity response features of cemented tailings backfill under repeated dynamic loading

Cemented tailings backfill is subjected to repeated dynamic disturbances in underground mines. This study investigated the effects of curing age, impact energy, and number of impacts on the dynamic mechanical response and microstructural evolution of cemented tailings backfill using drop-weight impact tests and scanning electron microscopy. Peak impact stress increased exponentially with curing age and impact energy. Its dependence on the number of impacts was energy dependent: at 6J, peak impact stress increased exponentially, whereas at 8–12J, it initially increased and then decreased, reaching a maximum at the second impact. Microstructural analysis showed that impact energy and number of impacts jointly governed pore compaction and damage accumulation. Peak impact stress was exponentially negatively correlated with apparent porosity and positively correlated with mean gray value. These findings clarify the macro–micro response mechanism of cemented tailings backfill under repeated impacts and support stability assessment under dynamic mining disturbances.