Failure characteristics of high stress rock induced by impact disturbance under confining pressure unloading

The failure characteristics under coupled static and dynamic loading were investigated by the improved split Hopkinson pressure bar (SHPB) with axial pre-pressure and confining pressure. The results show that the stress-strain curve of the rock under static-dynamic coupled loading is a typical class I curve when the dynamic load is comparatively high; With the decrease of the dynamic load, the stress-strain curve transforms to a typical class II curve. The dynamic failure process was recorded by high-speed photography. Analyses of fracture surface morphology show that the failure modes of specimens are tensile failure or combined shear failure when the impact load energy is low, but the failure modes of specimens become tensile failure when the impact load energy is high. The results of fractal dimension show that the elastic potential energy release leads to increase in the degree of crushing of samples when the energy of impact load is low under coupled static and dynamic loads with high stress.