Dynamic mechanical characteristics and fracture mechanism of gas-bearing coal based on SHPB experiments

To investigate the dynamic characteristics and fracture mechanisms of gas-bearing coal samples, a split Hopkinson pressure bar experimental system (SHPB-GAS) was built, using which dynamic impact experiments of gas-bearing coal were performed. Stress wave signals were collected and processed to analyze changes in strain characteristics with time. Relationships between dynamic strength, failure strain, and various factors such as axial static load, confining pressure, gas pressure, and impact load were analyzed. Our results show that dynamic strength and failure strain increased with the increase of confining pressure and impact load, but decreased with the increase of axial static load and gas pressure. Furthermore, evolution of dynamic cracks and failure mode of gas-bearing coal were analyzed, with the results indicating that samples presented axial tension fracture under the combination loading (axial static load, confining pressure, gas pressure and impact load). The effects of these four factors on the fracture evolution in coal samples were then discussed. Under these conditions, the fracture mechanism of gas-bearing coal was investigated and the effects of shear stress and normal stress on the fracture surface were illustrated. Our findings show that gas flow over the coal surface will increase shear stress along the fracture surface, in turn inducing coal fracture.