Fracture Development Mechanism of Water‐Isolating Soil Layers During Downward Mining of Shallow‐Buried Coal Seam Groups

ABSTRACT

Roof water inrush induced by fracture development in water‐isolating soil layers poses a severe hazard during the downward mining of shallow‐buried coal seam groups. Using Hanjiawan Coal Mine as the engineering case, this study systematically investigates fracture evolution mechanisms under the coupled effects of repeated mining and groundwater seepage through theoretical analysis, physical similarity simulation, and numerical modeling. The results reveal that the water‐isolating soil layer exhibits depth‐dependent “state anisotropy,” with a boundary at approximately 23 m separating a plastic upper layer (core fracture zone) from a bedrock‐like lower layer. Fracture propagation in the upper layer is governed by mining‐induced stress redistribution and groundwater seepage and is characterized by point‐source and line‐source infiltration. Fractures exhibit healing behavior under the combined effects of stress recovery and water‐induced clay expansion, resulting in the formation of a central compaction zone. A fracture propagation–healing mechanical model indicates that the maximum fracture depth is 17.98 m. This value agrees well with the results of physical similarity simulation (17.10 m) and numerical simulation (17.35 m), with deviations of less than 5%. This study elucidates the dynamic evolution of fractures under mining–seepage coupling and provides a theoretical foundation for evaluating the stability of water‐isolating strata and preventing roof water inrush during water‐preserving mining.