Numerical study on instability characteristics and influencing factors of inclined rock–coal–rock composite structures

Failure and instability of inclined rock–coal–rock composite structures (IRCRS) are critical contributing factors to impact-induced mining disasters, particularly in scoured coal seams. This study utilizes the UDEC numerical modeling approach to investigate the failure mechanisms of IRCRS. Systematically analyzing the failure and instability modes, associated characteristics, and the influence of various parameters. The primary findings are as follows: (1) The failure and instability modes of IRCRS can be classified into three distinct types: Fragmentation instability (FI), single contact surface slip and fragmentation instability (SSI), and double contact surface slip and fragmentation instability (DSI). (2) Although the peak strength of FI exceeds that of slip-induced instability, the extent of fracture damage is more severe during slip instability. In such cases, the composite structures exhibit a characteristic “low stress and high energy release” behavior. (3) As the inclination angle of the contact surfaces, surface roughness, and the mechanical strength of the coal and rock increase, the propensity for slip instability rises, the degree of fracturing diminishes, and the peak stress required to trigger structural failure decreases. These findings contribute to a deeper understanding of failure processes in scoured coal seam mining environments and provide a theoretical foundation for preventing rockburst disasters caused by structural instability.