Mechanical characteristics of unloading rock under coupled dynamic and static loads

In order to study the mechanical behaviors of the surrounding rock of underground projects subjected to dynamic disturbance after excavation, sandstone specimens are loaded, unloaded, secondarily loaded and impacted by use of the coupled dynamic and static loading split hopkinson pressure bar (SHPB) system. Firstly, the sandstone specimens are loaded with different triaxial compressions, confining stresses of 2, 4, 6, 8 MPa, and axial compression stress of 95% of the corresponding triaxial static compressive strength. Secondly, they are unloaded to 20%, 30%, 60%, 70%, 80% and 90% of the corresponding triaxial static compressive strengths. Finally, the impact loading tests with the same amplitude along the axial direction are carried out. From the experimental results, when loading and unloading to 90% of the corresponding triaxial static compressive strengths, the rock homogenization hypothesis is not applicable. The compressive strength of rock increases with the confining pressure when loaded under coupled dynamic and static stresses. When the confining pressure is constant and the axial static pressure increases, the compressive strength of rock increases at first and then decreases. The impactenergy absorbed by rock failure gradually decreases with the increasing axial static pressure and increases with the increasing confining pressure.