Analysis of the Dynamic Impact Mechanical Characteristics of Prestressed Saturated Fractured Coal and Rock

The natural and water-saturated states of coal samples under static and static-dynamic loads were tested using the Split-Hopkinson pressure bar (SHPB) method and RMT-150 system, respectively. The differences in the strength reduction coefficient and elastic modulus reduction coefficient of water-saturated coal samples under static and static-dynamic loads were discussed. The experimental results for coal were compared with the corresponding characteristics of typical sandstone samples under static and static-dynamic loads. Furthermore, a fracture model of a hydrous wing branch fracture under static-dynamic loading was established based on the theory of fracture damage mechanics. The difference in dynamic strength between coal and sandstone samples for both the natural state and water-saturated state was analyzed. On this basis, the effect of water on the fracture surface of coal and the tensile strength and shear strength of the branch fracture surface were fully considered. In addition, criteria of the branch fracture surface for crack initiation and crack arrest were also established. Finally, the phenomenon of increasing elastic modulus in saturated coal samples was explained with this criterion