Analysis of the development height of the “two zones” and separation layers in overburden strata under repeated mining of close distance coal seams

Regarding the failure of overburden strata and the development height of the “two zones” under repeated mining in close-distance coal seams, and to prevent various safety incidents such as roof water inrush and spontaneous combustion in goafs caused by water-conducting and air-leakage channels during face extraction, this study takes a mine in the Ordos region as the engineering background. By employing empirical formula prediction, drilling fluid loss measurement, borehole televising, numerical simulation, and intelligent prediction methods, the impact of repeated mining on the development patterns of the “two zones” in overburden strata and the evolution of separation spaces was analyzed. The research indicates that repeated mining in close-distance coal seams significantly increases the development height of the “two zones” in the overburden strata. The development height of the “two zones” far exceeds that resulting from the extraction of the upper coal seam, exhibiting a step-like increase with abrupt jumps between stages. The development characteristics of separations follow the sequence: “development of low-position separations → closure of separations → development of high-position separations → closure of high-position separations”. The error between the predicted value from the empirical formula and the field-measured value was considerable, whereas the relative errors compared with the numerical simulation and intelligent prediction values were only 1% and 3%, respectively, verifying the prediction accuracy. The findings can provide references for mining operations in similar working faces and analogous engineering contexts.