Experimental research into the dynamic damage characteristics and failure behavior of rock subjected to incremental repeated impact loads

The damage to rocks caused by frequent disturbance loads is a major issue in rock engineering. Understanding the failure behaviors and establishing the dynamic energy-damage model of rock under constant and incremental repeated impact loads are key to the structural safety and stability design of rock mass engineering works. In this work, the split Hopkinson pressure bar (SHPB) system and an ultrasonic measuring system were used to test constant and incremental repeated impact loads on red sandstone. The damage evolution of red sandstone was revealed under constant and incremental repeated impact loads, the energy-damage model of constant and incremental repeated impact loads was established, the crack expansion pattern and fatigue failure properties were studied, and the changing trend of the critical damage amount and the fractal characteristics of block after fatigue failure were investigated. The experimental results show that: the dynamic strength of red sandstone shows an overall decreasing trend with the impact velocity and the number of impacts under constant repeated impact loads. The damage evolution of the specimens follows an inverted S-shaped pattern of development. The critical damage amount is negatively correlated with the impact velocity. As the impact velocity is increased, the crack expansion velocity and main-body block size of the specimens after destruction increase. Under incremental repeated impact loads, the dynamic strength of red sandstone increases with the velocity incremental gradient and the number of impacts, and the damage to the specimens shows an accelerated upwardly concave trend. The critical damage amount and the incremental gradient demonstrate an alternating trend of negative-positive correlations. The crack expansion velocity is gradually accelerated, and the main-body block size of specimens after destruction displays a trend of growing and then reducing with the incremental gradient.