A study on overburden movement and the "Three Zones" in a composite goaf of closely-spaced shallow coal seams

• Surface subsidence in overlapping mining areas was twice that of single-seam mining. • A unique overburden movement pattern was found in shallow, closely-spaced coal seams. • Key airflow paths leading to spontaneous combustion hotspots in mined areas were identified. Repeated mining in shallow-buried, closely-spaced multi-seam groups induces complex cascading hazards, including secondary surface subsidence and increased goaf fire risks. To systematically investigate the distribution patterns of overburden movement, surface subsidence, and spontaneous combustion risk zones under such conditions, this study examines the composite goaf formed by Panels 12204 and 22206 in the Huojitu Mine using an integrated approach of numerical simulation, theoretical analysis, and field measurements. The results indicate that multi-seam interaction induces secondary compressive deformation in the overburden, reducing the caving angle by 9°. The magnitude of secondary subsidence in the overlapping goaf area is approximately twice that in the non-overlapping area. The complex three-dimensional fracture network formed by repeated mining significantly enhances air leakage through the surface and interlayer pathways, leading to a notably longer oxidation zone compared to single-seam mining. Furthermore, the upper coal seam exhibits a larger oxidation zone area and consequently a higher risk of spontaneous combustion. Based on these findings, this study provides a theoretical foundation and practical recommendations for the targeted prevention and control of such hazards under similar mining conditions.