Overburden breakage and surface damage evolution under high-intensity mining of shallow coal seams: evidence from Shendong mining area.

During high-intensity mining of shallow coal seams, severe overburden movement and surface subsidence can lead to geological hazards like ground fissures. This study investigates these phenomena at a representative working face in the Shendong mining area. Numerical simulations were conducted to analyze overburden displacement, stress distribution, fracture evolution, breakage characteristics, and surface subsidence under varying mining advance distances. A theoretical model of overburden breakage and surface subsidence was developed, revealing the key mechanisms involved. Results indicate that overburden breakage and collapse occur in distinct stages. The presence of key strata is essential for maintaining the rock layer stability and controlling surface subsidence. Initial roof breakage occurs at an advance distance of 80 m, with periodic intervals of 40 to 60 m. Stress distribution evolves through three stages: overall pressure relief, single-peak stress concentration, and double-peak stress concentration. Fractures propagate through the overburden, ultimately reaching the key strata and surface. Once the key strata are fractured, a "voussoir arch" structure suppresses further fracture expansion. The theoretical model and simulations align closely with field data, providing a scientific basis and technical support for controlling subsidence and facilitating surface ecological restoration during high-intensity mining.