Rotation movement law of overburden structure and design of reasonable stopping caving parameter during end-mining of fully mechanized caving in close-distance coal seams

During the end-mining stage of a longwall top coal caving face in closely spaced coal seams, load transfer from overlying remnant coal pillars can significantly affect the surrounding rock. The prolonged equipment withdrawal process further aggravates rock deformation and failure. To clarify how end-mining parameters control surrounding-rock stability, this study takes the N0381 working face of Yanzishan Coal Mine as the engineering background. Field monitoring, theoretical analysis, and numerical simulation are combined to investigate the rotational behavior of key blocks in the main-roof under non-uniform loading from a remnant coal pillar. The corresponding control mechanism of surrounding-rock stability is also examined. A prevention and control strategy is proposed by coordinating three factors: the overburden conditions during end-mining, the top-coal stopping-caving distance, and the position of the main-roof fracture line. The strategy was subsequently applied to guide production at the N0383 working face. The results show that the overlying remnant coal pillar changes the load distribution on the main key stratum of the lower coal seam during the end-mining stage. It also affects the rotational response of the key block. The retracement channel should avoid the abrupt load-transition zone near the remnant coal pillar. It should preferably be arranged in an area with a relatively stable load distribution. The top-coal stopping-caving distance affects strata-pressure behavior during end-mining by regulating the rotation angle and angular velocity of the key block. A Type II stopping distance can provide a balance between surrounding-rock stability and the top coal recovery rate. The position of the main-roof fracture line also has a significant influence on roof deformation and stress distribution around the retracement channel. When the fracture line is located directly above the retracement channel, the risk of surrounding-rock instability increases. Field application at the N0383 working face showed that the retracement channel could be safely arranged beneath the goaf with a top-coal stopping-caving distance of 18 m. Under these conditions, surrounding-rock deformation met the requirements for safe equipment withdrawal.