Confinement effect of dynamic failure of red sandstone under impact

In order to study the disturbance caused by blasting in the surrounding rock of the deep tunnel during the tunneling process, it is urgent to understand the mechanical response, failure mode and energy dissipation characteristics of the surrounding rock under dynamic load. In this study, the dynamic compression test of red sandstone samples under confining pressure was carried out by using the self-developed Hopkinson pressu re bar (SHPB) test system equipped with active confining pressure control device to explore the dynamic mechanical response, failure mode and energy dissipation mechanism of red sandstone under blasting impact load. The test results show that the dynamic stress-strain curve of the rock sample without confining pressure shows the characteristics of "two-stage" change, while the "three-stage" evolution law is obvious under confining pressure. The confining pressure significantly increases the dynamic compressive strength and peak strain of red sandstone, and the two show obvious strain rate and confining effects. In terms of failure mode and energy dissipation, when there is no confining pressure, the rock specimens undergo crushing failure under the action of higher strain rate. Under the confining pressure condition, the damage degree of the specimen was significantly reduced, and finally the compression and shear failure mode was reduced. At the same time, under the same strain rate, the energy absorption capacity of the confining pressure specimen is significantly higher than that without confining pressure. When the incident energy is similar, the specific energy absorption value (SEA) of red sandstone increases with the increase of confining pressure level.