Experimental study on dynamic mechanical characteristics of coal body under dynamic–static combination loading

The mechanical response characteristics of the coal body in deep coal mining faced under dynamic loading impact are significantly different from those under static conditions, which leads to an increase in the frequency and intensity of dynamic disasters in deep coal bodies. For this reason, a separated Hopkinson compression bar test system with a high-speed camera and axial and confining pressure loading systems was utilized to study the dynamic mechanical characteristics of the coal body under combined dynamic and static loading. The test shows the following results. (1) The stress–strain curve of the coal body under uniaxial dynamic–static combined loading conditions can be divided into elastic stage, crack extension stage, rapid extension stage of crack instability, post-peak stage, and rebound stage, while the stress–strain curve of the coal body under triaxial dynamic–static combined loading conditions can be divided into compaction stage, elastic deformation stage, plastic deformation stage, and unloading stage. (2) The dynamic strength of the coal body under uniaxial dynamic–static combined loading conditions increases and then decreases with the increase in static axial pressure; the impact velocity and confining pressure under triaxial dynamic-static combined loading have obvious reinforcing effects on the dynamic strength of the coal body. (3) The degree of coal body crushing increases with the increase in impact velocity, but the larger the confining pressure is, the lower the degree of destruction of the specimen is. The research results provide theoretical support for revealing the dynamic destabilization mechanism of deep coal and rock bodies.