Experimental research on coal and rock strength deterioration under combined static and dynamic triaxial loading

Based on the servo-triaxial compression test system of coal and rock mechanics, supplemented by acoustic emission detection, a dynamic load test of coal and rock under high stress at different frequencies in Binchang mining area was carried out to study the failure mechanism and strength degradation law of coal and rock induced by dynamic load. The results show that the strength of coal and rock is obviously degraded after dynamic load disturbance. The peak strength and strain are negatively correlated with the dynamic load frequency; after the dynamic load disturbance, the internal cracks in the coal and rock further develop and enter the yield deformation ahead of time; the failure of coal and rock first starts from the inside and gradually extend to the surface, the failure mode changes from shear failure to transverse tensile failure. Acoustic emission positioning points extend from the center to the outside and are distributed in large numbers on the surface of coal and rock, which are basically consistent with the development area of coal and rock fissures and the main failure directions; acoustic emission energy events mainly occur in the initial stage and peak stage of dynamic load loading and reach the maximum in the peak stage, the energy value is positively correlated with the stress level of coal and rock, and the energy drops rapidly after failure. After the coal dynamic loading is over, the silent emission energy event occurs before the static load continues to the maximum stress stage of the dynamic load, and the obvious Kaiser phenomenon occurs; the acoustic emission energy drops rapidly near the peak failure stage, this feature can be used as a precursor to predict coal and rock failure.