Dynamic Load Mechanical Properties and Energy Characteristics of Rock–Coal Combination With Different Lithologies: A Laboratory Investigation

To address the substantial mining pressure from unstable rock formations, impact compression tests were performed on coal–rock combination specimens of varying strengths using a split Hopkinson pressure bar (SHPB). The dynamic mechanical properties, energy dissipation patterns, and failure modes of the specimens were systematically analyzed, illuminating the mechanical behavior and energy conversion mechanisms of coal–rock combination under both dynamic and static loading conditions. The findings reveal a positive correlation between the proportion and strength of rocks within the coal–rock combination and its compressive strength as well as elastic modulus. From an energy perspective, at impact velocities below 10 m/s, the energy consumption due to the fragmentation of coal–rock combination of varying strengths rises significantly, ranging from 0.15 to 0.30. The greater the height and strength of the rocks within the coal–rock combination, the more pronounced the dynamic phenomena observed following the failure and instability of the coal–rock mass. The existence of a hard roof serves as a critical driving force for dynamic coal–rock disasters. For coal seams with identical strength, an increase in rock strength leads to greater energy expenditure in crushing the coal and rock mass under dynamic loading conditions. In engineering practice, coal seams beneath a hard roof are more susceptible to severe crushing under dynamic loading, thereby, increasing the likelihood of strong ground pressure events.