Experimental and numerical investigation on the mechanical responses and cracking mechanism of 3D confined single-flawed rocks under dynamic loading

Accurately characterizing the mechanical responses and cracking mechanism of three-dimensional confined fractured rocks under coupled static-dynamic loading is of paramount importance for underground engineering construction. Using a modified split Hopkinson pressure bar (SHPB) system, five groups of single-flawed specimens with the axial prestress ratio from 0 to 0.8 are tested at the strain rates in the range of 65–205 s−1 under a fixed radial prestress. Our results indicate that both the dynamic strength and total strength show significant positive linear correlations with the strain rate, and the dynamic strength shows more strain rate sensitivity under higher axial prestress. The dynamic strength and corresponding failure strain decrease with increasing axial prestress, while the total strength is barely affected by the axial prestress. The dynamic elastic modulus initially increases before the axial prestress ratio reaches 0.6 and then decreases. The failure pattern of tested specimens changes from single diagonal failure to an "X" shaped conjugated failure as axial prestress increases. Furthermore, the progressive cracking processes of confined single-flawed specimens under different axial prestresses are numerically visualized by the discrete element method (DEM). Based on the displacement trend lines on both sides of cracking surface, five crack types are identified and classified in our simulation. The displacement field distributions of the DEM models reveal that the macroscopic single diagonal failure under lower axial prestress is mainly controlled by mixed tensile-shear cracks, while the "X" shaped conjugated failure under higher axial prestress is shear dominated.