Research on the strata movement laws of deep multi-seam mining in super-thick and weak cementation overburden

Taking the Yingpanhao Coal Mine as the geological prototype, a FLAC-PFC coupled numerical model was established based on measured mechanical parameters. The model was calibrated and validated using field leveling data, and both macroscopic movement patterns and microscopic failure processes were analyzed in combination. This approach was applied to investigate in depth the influence of interlayer spacing and pillar offset on the strata movement mechanism during deep multi-seam mining under extremely thick and weakly cemented overburden. Results demonstrate a strong correlation between pillar offset and surface movement parameters. Increasing the offset reduces the maximum subsidence angle. As extraction progresses, the stress arch evolves from a single to a multi-arch structure, with surface subsidence following a Boltzmann function. An offset ≥45 m promotes a stable masonry beam structure that effectively controls subsidence, whereas a 30 m offset causes stress concentration and roof cutting. The optimal offset is determined to be 45 m, balancing pressure relief and settlement control. During repeated mining, a decreasing depth-to-thickness ratio enhances the load-bearing capacity of middle strata; however, at a ratio of 11, overall bending induces a sharp settlement increase. These findings provide theoretical and practical guidance for repeated mining under similar geological conditions..