Instability mechanism of composite structure involved coal pillar and key strata induced by multi-face mining

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The complex instability mechanism of large-space stope structure formed by multi-face mining poses significant risk of mining-induced seismicity. Aiming at the composite structure of a mine in Shanxi, China, a mechanical model is established and the instability mechanism are investigated. The instability condition was explored, and the instability process was simulated. The theoretical results were verified with the field monitoring, and the main influencing factors of this instability were analyzed. The results indicate that in large-space stope, the coal pillar, which serves as the primary load-bearing structure, interacts with the key strata. Individual instability could induce interactive instability, resulting in the instability of composite structure. The stiffness of coal, the width of coal pillar and the strength of key strata rock mass have significant effects on the stability of composite structure. Taking measures against these factors can prevent the instability of composite structure from the perspective of preventing the instability of coal pillar and reducing the energy release of key strata instability. The results could contribute to the further exploration of the stability of large-space stope.