Stability and ground pressure behavior of key layers during shallow close-distance coal seam mining through coal pillars

To address the problems of key layer instability and intense ground pressure during mining under overlying concentrated coal pillars in shallow buried close-distance coal seams, this study takes the 12,101 working face of Halaigou Coal Mine as the research object. By comprehensively adopting methods such as theoretical analysis, similarity simulation experiments, numerical simulation, and field monitoring, it reveals the stability evolution law of the key layer and the characteristics of ground pressure manifestation during the coal pillar crossing stage. The research indicates that the overlying coal pillar causes stress concentration in the hinged structure of the key layer, and its rotational instability is the main cause of inducing dynamic ground pressure. During the entry stage into the coal pillar, the main key layer block is subjected to horizontal thrust and shear force; when the rotation angle exceeds the critical value, structural instability triggers roof slippage. During the exit stage from the coal pillar, the sub-key layer fractures and rotates due to disturbance from empty roadways, leading to intensified periodic weighting. Similarity simulation experiments based on fiber Bragg grating monitoring show that the overlying strata collapse exhibits a concave Brillouin frequency shift characteristic, with the peak frequency shift coinciding with the fracture line location and the strata subsidence reaching 48.3 mm. Numerical simulations indicate that the vertical stress concentration factor during the coal pillar crossing stage is as high as 3.21, and the plastic zone of the coal pillar is dominated by shear failure. Field monitoring verifies that the dynamic load factor during the entry stage into the coal pillar reaches 1.62, the peak support resistance reaches 9,672 kN, and the weighting duration increases significantly. The research results provide theoretical support and technical guidance for the safe and efficient mining of shallow buried coal seams.