Research on force chain transfer law of overlying rock and strong mining pressure control under the collaborative breaking effect of double key layers

The mechanism of strong mining pressure of thick coal seam under dual key strata conditions mining is unclear, making the prediction of weighting intervals and disaster control difficult. Taking the 11223 working face in the Huainan mining area as an engineering case, the overburden migration patterns and dynamic force chain transfer mechanism under synergistic fracture of dual key strata were investigated by integrating discrete element numerical simulation, theoretical analysis and field practice. A support-surrounding rock bearing model for dual key strata fracture was established. The results demonstrate that the lower key stratum I, directly affected by mining disturbances, exhibits periodic fracturing with an average interval of 25 m, forming a "cantilever-step rock beam" composite structure that triggers minor periodic weighting. In contrast, the upper key stratum II, influenced by stress transfer hysteresis, breaks at an interval of 40 m with a fracture angle of 73°. Its instability induces transfer amplitude of kinetic energy up to 4.2 times the initial value, causing the peak abutment stress to surge to 48 MPa (28% exceeding the rated support resistance), which is identified as the primary cause of major periodic intense mining pressure. The fracture of dual key strata governs stress field evolution through force chain network reconstruction. Fracture of key stratum I forms a localized "pressure arch" structure, while fracture of key stratum II triggers asymmetric tension-compression alternation, driving the stress field through a three-stage evolution of "local unloading, regional transfer, and global reconstruction". A deep-hole pre-splitting blasting weakening scheme was proposed based on dynamic load superposition mechanisms. After field implementation, periodic weighting intervals decreased from 25 m to 16 m, the dynamic load coefficient of supports decreased from 1.5 to 1.3, and the peak roof pressure recuded by 46.7%. These findings provide theoretical and practical insights strong mining pressure control in deep multi-key strata coal mines.