Surface subsidence characteristics and controlling effects of overburden structure during deep coal mining in an ecologically fragile region of western China

Deep coal mining in ecologically fragile regions can trigger complex surface subsidence processes and significantly impact the geological environment. In the western Ordos Basin of China, deep coal seams are overlain by thick aeolian sand and multi-layered weakly cemented sandstone, leading to highly variable surface deformation responses to underground mining. However, the coupled effects of mining scale evolution and overburden structural configuration remain poorly constrained. In this study, the Yingpanhao Coal Mine in the Shaanxi–Inner Mongolia border region was investigated using long-term high-precision leveling observations combined with three-dimensional FLAC3D numerical simulations. The spatiotemporal evolution of surface subsidence was analyzed under different mining stages, with particular emphasis on working face geometry, adjacent continuous mining, and typical overburden combination structures. The results show that for a single working face with a width of 300 m, the critical mining length along the strike direction is approximately 1800 m. During adjacent continuous mining, surface deformation exhibits a pronounced stage-transition behavior, with a critical width-to-depth ratio of about 1.22 marking rapid evolution toward full subsidence. The thickness of the aeolian sand layer mainly controls early-stage subsidence development, whereas the thicknesses of the high-level Cretaceous weakly cemented sandstone and the low-level Jurassic Zhiluo Formation sandstone dominate the intensity and spatial continuity of surface movement and deformation. In this fragile aeolian-sand environment, the evolving basin may also disturb the shallow groundwater system—fracture-induced leakage and altered recharge can locally depress the water table, while drainage impedance in the compressed center may promote secondary salinization—such that ecological impacts tend to be zoned between the tensile margins and the basin floor. These findings provide important insights for subsidence prediction and environmental management in deep coal mining areas.