Dynamic characteristics and deterioration mechanism of coal under distinct initial gas pressure

Abstract Additional to dynamic and static superimposed loads, gas effects frequently affect coal seams throughout the coal mining process. It is crucial to comprehend coal samples’ mechanical properties and deterioration mechanisms under distinct initial gas pressure conditions. Consequently, the dynamic compression experiment of coal samples was conducted utilizing a self-developed observable combined dynamic and static loading test system of gas-bearing coal (GAS). The mechanical characteristics including failure mode in coal samples under distinct initial gas pressures were studied. Furthermore, the mechanism of gas deteriorated mechanical parameters and aggravated the propagation of cracks when combined with dynamic and static loads was revealed. The conclusions are drawn as follows: The GAS can go through four stages of deformation: elastic stage, elastoplastic stage, plastic stage, and failure stage. Furthermore, the dynamic strength and failure strain deteriorated with increasing gas pressure. Based on computed tomography (CT) technology, it is found that the splitting-spallation composite cracks of impacted samples become more noticeable with rising initial gas pressure, and finally, the two kinds of cracks create a complex reticular crack system. Meanwhile, the crack volume and fractal dimension increase with rising gas pressure, indicating that gas can aggravate the coal’s failure degree. Under combined dynamic and static loads, the deterioration model of mechanical parameters of GAS is obtained, that is, with rising initial gas pressure, the dynamic strength of coal samples reduces and the failure strain rises synchronously. The main reason for the aggravation of compound failure in impacted samples is that the stress intensity factor rises with the rise of gas pressure. These conclusions enrich the basic theories such as the inducing mechanism of dynamic disasters caused by coal-rock-gas compounds and can offer a theoretical foundation for the technology employed in monitoring, early warning, and prevention of dynamic disasters in compounds.