Background The heights of water flowing fractured zones represent a key concern in the prevention and control of water disasters occurring in mining face roofs and water resource protection of coal mines. Varying lithologies and structures of the overburden are identified as primary factors governing the height and characteristic differences of water flowing fractured zones.
Methods Against the engineering background of a mining face with 10 m super-large mining height in the Caojiatan Coal Mine of Shaanxi Province, this study investigated the differences in the mining-induced responses of the soil-bedrock-type overburden using numerical simulations of stress-seepage coupling and measured heights of water flowing fractured zones in the overburden. Furthermore, this study proposed a water-controlled mining strategy in the presence of composite water bodies in the roof and analyzed the performance of mining using this strategy.
Results and Conclusions The results indicate that the roof of the mining face with 10 m super high mining height represents a typical overburden structure of the soil-bedrock type. The laterites in the overburden enable fracture healing, resulting in repeat water resistance and thus inhibiting mining-induced fractures. Accordingly, the fractured zone/mining height ratio of the mining face is 22.56, and mining-induced fractures largely propagate below the laterites. Although very few fractures extend to laterites, the overall water resistance of the laterites remains. In this case, the bedrock and laterites exhibit the variation pattern of traditional water flowing fractured zones. Based on the analysis of the evolution of mining-induced failures in the overburden and the water filling pattern of the roof aquifer, this study proposed a water-controlled mining strategy consisting of the precise drainage of static reserves, increased discharge and water diversion for dynamic supply, full-space flow field monitoring, and the prevention of local roof cutting and leakage. A comprehensive analysis of multiple factors, including water levels in long-term hydrological observation holes, water inflow along the mining face, and hydrochemistry during the mining process, reveals that the mining-induced fractures only propagated to bedrock fissures and the aquifer in the weathering zone, while the Quaternary aquifer was unaffected by mining. These contribute to the safe and efficient water-controlled mining of the mining face with a super-large mining height. The results of this study can provide a basis for the prevention and control of the overburden failure and water disasters, as well as water resources protection, in mining with super-large mining heights and high mining intensity in China.
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