Experimental study on energy dissipation and failure characteristics of rock at depth under non-hydrostatic pressure condition

Deep buried rock is often in a non-hydrostatic initial ground stress field, and the different stress states lead to different rock response under dynamic loading. To study the dynamic behavior of rocks under coupled non-hydrostatic pressure and dynamic loading, the dynamic compression tests under different initial stress are carried out by using the split Hopkinson pressure bar (SHPB) experimental system, and the influence of different non-hydrostatic pressure on energy dissipation and failure characteristics of rock is analyzed. Based on the test results, it is found that both axial and lateral confining pressure have a significant impact on the rock dynamic strength. Taking 8 MPa as the critical point, the rock dynamic strength first increases and then decreases with the increase of axial confining pressure, but the rock dynamic strength will continue to increase with the increase of lateral confining pressure. The rock dissipative energy gradually decreases with the increase of axial confining pressure, but the trend of dissipative energy changes with confining pressure is complicated. When the axial confining pressure is low, the dissipative energy decreases with the increase of the confining pressure, and when the axial confining pressure is high, the dissipative energy shows a characteristic of increasing first and then decreasing with the increase of lateral confining pressure. According to the apparent and internal damage patterns of the specimens, combined with fractal theory and CT scanning technology, the influence of the damage pattern of rocks under different non-hydrostatic pressure conditions is analyzed. It is found that there is a significant correlation between the apparent cracks of rock and the ratio of axial-confining pressure. When the axial confining pressure ratio is low, there are fewer cracks on the side and end faces of rock. With the increase of the axial confining pressure ratio, the number of apparent cracks of rock increases. Through the analysis of the cross-sectional and vertical slices of the rock, it is found that there are circumferential and radial cracks in the rock simultaneously, and the rock failure is controlled by the penetrating shear cracks. It also can be found that the damage of rocks under non-hydrostatic pressure conditions can be divided into two parts: the central spherical rock mass and the peripheral broken rock mass, and the damage degree of rocks increases when the axial pressure increases, while the elevation of the surrounding pressure makes the damage degree of rocks decrease.