Mining-induced void distribution and application in the hydro-thermal investigation and control of an underground coal fire: A case study

• Void rate distribution models of mining-induced voids were proposed.
• Longwall coal mining-induced voids present a “fractured dome” distribution.
• A correlation between surface anomaly and fire source behavior was expressed.
• A new PDCA cycle with FAHP and AHP embedded was applied to fire-fighting engineering.
• An approximately 115,200 m2 fire zone was successfully controlled.

Mining-induced voids are a necessary factor triggering underground coal fires that endanger the underground and atmospheric environment. On the other hand, voids provide channels for underground fluid and fire-fighting material migration. A series of void rate models were proposed to determine the three-dimensional heterogeneous distribution of the mining-induced voids in the disturbed strata. The void rate distribution map of horizontal voids presents a reversed “quadripod-type” shape in the strata plane, the void rate of vertical voids has a shape similar to two “basins” of different sizes and contrasting opening directions nested together, and the void rate of isotropic pores presents a “basin-type”. It can be deduced from the distribution maps that were calculated by theoretical and numerical models that the voids present a “fractured dome” distribution and that the void rate gradually decreases from foot to crown of the dome. It was ascertained from the application of void rate models in the hydro-thermal investigation of an underground coal fire that the correlation between heat production and ground surface temperature presents a linear function, while that between outflow velocity and fire source temperature has a negative-exponential-power relationship. Additionally, a new Plan-Do-Check-Adjust cycle was established for the management of fire-fighting engineering, which includes the delineation of fire zones, the evaluation of fire behavior, the optimization of fire-fighting measures, the performance of the fire-fighting plan, and the assessment of control results to determine whether the fire-fighting plan should be reformulated or improved. After five control cycles lasting nine months, an approximately 115,200 m2 fire zone was controlled.

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