Dynamic behavior of coal under true triaxial prestressed by using a Hopkinson bar

Deep mining is faced with severe rock dynamic problems. Coal bears high-strength static load in the deep and is prone to impact under the influence of dynamic load disturbance such as roof breaking. The true triaxial Hopkinson pressure bar system is used to conduct dynamic load impact tests on coal specimens under different triaxial prestressing forces to simulate the bearing characteristics of coal under different engineering conditions. The results show that the dynamic mechanical characteristics of coal are confinement-dependent under the same dynamic load, and the energy transmission of each component are significantly different, which is obviously different from that under static load; Furthermore, the influence range of intermediate principal stress on dynamic characteristics of coal specimen is 6~8 MPa. Based on the failure characteristics, the enhancement of the intermediate principal stress will increase the integrity and the internal damage of a coal specimen after failure; It should be noted that the strain signals obtained in the Y/Z axis direction are mainly the response to the triaxial prestress, and the stress wave of coal specimen is mainly influenced in the impact direction. In underground coal mining, by changing the triaxial prestressed state of coal, the buffering effect of stress wave is improved, and the damage of coal caused by the impact is reduced.