Study on the Failure and Instability Mechanism of Coal–Rock Parting–Coal Structures under Unloading

Rockburst with structural instability is prone to occur during mining and excavation in the bifurcation area of coal seam. It is crucial to explore the failure and instability characteristics and mechanism of coal–rock parting–coal structure (CRCS) in order to prevent rockburst occurrences. The following four points are addressed: (1) The failure and instability of the CRCS involve slip and fracture characteristics, which are influenced by factors such as the strength of the coal and rock parting, inclination angle, friction coefficient, and surrounding rock pressure. (2) The failure and instability of the CRCS encompass fracture instability (FI), single and double contact surface slip and fracture instability (SSI and DSI). Rockburst manifests as strain instability in the form of FI, along with structural instability in the form of SSI and DSI. (3) Crack development is primarily characterized by shear cracks supplemented by tensile cracks. However, it is the connecting effect of tensile cracks that serves as a primary cause for macro-instability within the CRCS. (4) A larger inclination angle on the contact surface results in more pronounced slip phenomena, leading to greater energy release. This demonstrates low strength but high release energy characteristics, making it difficult to predict rockburst occurrences. The research results have important theoretical significance for preventing rockburst in the bifurcation area of coal seam.