Experimental investigation of dynamic mechanical characteristics of inhomogeneous composite coal-sandstone combination for coalbed methane development

In deep resource exploitation, the coal seam and the strata are jointly loaded, forming a systematic combined structure that can have a significant effect on coalbed methane (CBM) development. Therefore, to understand the deformation and damage characteristics due to blasting load of the complex and real ground conditions, the 50 mm split Hopkinson pressure bar (SHPB) was used to study the dynamic performance and energy changes of coal-sandstone combination and sandstone-coal combination as inhomogeneous materials. In addition, high-speed photographic equipment was employed to determine the damage failure mechanisms. The results showed that the dynamic compressive strength and failure strains of two combinations showed polynomial relationships with increasing strain rates. The strain rate effects and likenesses of the two combinations' energy and energy rates were substantial. Furthermore, for the coal-sandstone combination, the initial damage fractures occurred at the end face near the bar, and at the interface for the sandstone-coal combination. Eventually, the improved constitutive model based on the ZWT was significantly consistent with the two combinations. The related theory can perform an effective and practical role in the mining of coal rocks under complex ground conditions for CBM development.