Abstract: In order to explore the difference in dynamic response of gas-bearing coal under impact loading, an observable gas-bearing coal split Hopkinson pressure bar (SHPB) test system was used to conduct uniaxial impact tests on coal bodies with different initial gas pressures. The energy dissipation law of the coal under different gas occurrence states was analyzed, and with the help of ultra-high-speed camera and digital image correlation (DIC) technology, the evolution characteristics of cracks on the surface of gas-bearing coal during the impact process were demonstrated. Combined with fractal theory, the influence of gas pressure on the fractal characteristics of crushed coal was obtained, and the intrinsic relationship between gas occurrence state and the characteristic size of crushed coal was revealed. The results show that under the impact loading, the stress-strain curve of the gas-bearing coal could be roughly divided into four stages based on the energy dissipation law. The deterioration effect of gas on the coal body was significant, and the crushing energy dissipation and crushing energy dissipation density function decreased exponentially with the increase of the initial gas pressure. Under the gas wedge effect, the evolution of the strain field of the gas-bearing coal subjected to the impact loading was more complicated, and the coal body damage gradually evolved from the transverse splitting failure to the composite transverse splitting-longitudinal splitting failure. Under the action of gas pressure, the internal damage of the coal body was intensified. After the failure, the average particle size and fragmented block size of the fragmented coal body gradually decreased with the increase in initial gas pressure. However, the fractal dimension increased exponentially, and the degree of coal body crushing was more intense. A multi-dimensional dynamic gas-bearing coal crushing model based on the conservation of energy consumption in the coal body crushing process was constructed, and combined with experimental data, the model was validated and it could better describe the characteristic dimensions of fragmented coal samples under the influence of gas. The research results have important theoretical significance and certain application prospects for the prevention and control of dynamic disasters in gas-bearing coal mines.

Key words: gas-bearing coal, impact loading, energy dissipation, digital image correlation (DIC), fractal characteristics, crushing model