Dynamic characteristics and energy evolution of granite subjected to coupled static-cyclic impact loading

In many underground rock projects, rock masses are subjected to coupled static-cyclic dynamic loading. In this paper, dynamic tests were carried out on granite specimens using a modified split Hopkinson pressure bar to study the dynamic characteristics and energy evolution of the rock under coupled static-cyclic impact loading. The results show that both the dynamic characteristics and the energy evolution of granite are sensitive to the number of repeated impacts and the confining pressure. Under the same confining pressure, the dynamic increase factor (DIF), dynamic elastic modulus, and transmitted energy ratio decreases, while the cumulative dissipated energy, cumulative specific energy dissipation and dissipated energy density tend to increase as more impact cycles are applied. The effect of confining pressure on enhancing the mechanical property of the rock is pronounced: the peak stress of rocks under confining pressure during cyclic impact is higher than their quasi-static compressive strength, and the DIF increase as the confining pressure increases. However, its effect on the dynamic elastic modulus is fairly insignificant. The confining pressure could change the crack propagation path of the specimens, and the failure mode is mainly a tensile failure, with no obvious axial splitting. By increasing the confining pressure, the energy dissipation capacity of the rock is significantly improved, and its increased rate of internal damage could be slowed down.