Dynamic response and failure mechanism of hydrostatically pressurized rocks subjected to high loading rate impacting

Abstract

In the deep underground, rocks are likely to subject to hydrostatic confining pressure by in-situ stresses and dynamic loading from earthquakes, blasts and impacts. Understanding the dynamic behaviors of rocks under coupled hydrostatic confining pressure and dynamic loading is thus crucial for disaster prevention and mitigation of deep underground engineering. Via the modified split Hopkinson pressure bar (SHPB) system, dynamic tests are conducted on hydrostatically pressurized sandstone specimens, with four confinements varying from 7 to 28 MPa and loading rates in the range of 1000–5000 GPa/s. Our results show that the dynamic strength of hydrostatically pressurized rocks is proportional to the loading rates and hydrostatic confinements, while the loading rate dependence of dynamic strength decreases as the hydrostatic confining pressure increases. The dynamic Young's modulus of rocks increases with increasing confinement, and it is independent of dynamic loading rate. Rocks are more fragmented under lower hydrostatic confinement or higher dynamic loading rate. Post-mortem examination of recovered specimens reveals that the failure pattern of hydrostatically pressurized rocks changes from the tensile-dominated failure to the shear-dominated failure with increasing confinement. Energy analysis indicates that more energy is needed to fracture the rocks under higher confinement or loading rate, while the energy utilization ratio of hydrostatically pressurized rocks reaches the maximum at certain intermediate loading rate.