Reconstruction of karst aquifer system beneath lower coal group and source-specific prevention and control technology for karst water disaster in Huainan Coalfield

The Huainan Coalfield boasts abundant coal resources, with an annual coal production of 80 million tons in 2022, making it one of China's major coal-producing regions in eastern China. The lower coal group in the Huainan Coalfield is characterized by large thickness, high coal quality, abundant reserves, and favorable occurrence conditions. However, the limestone beneath the lower coal group exhibits significant thickness, high confining pressure, strong water yield property, and uneven karst development, posing critical threats to mining operations. Based on the hydrogeological characteristics beneath the lower coal group, this study re-recognizes and reconstructs the karst aquifer system and proposes "source-specific prevention and control" technologies for karst water disasters. The research findings are as follows: The karst aquifer system beneath the lower coal group in the Huainan Coalfield, from top to bottom, consists of C₃Ⅰ aquifer, upper aquiclude of Taiyuan Formation, C₃Ⅱ aquifer, lower aquiclude of Taiyuan Formation, C₃Ⅲ aquifer, Benxi Formation aquiclude, and Ordovician limestone aquifer. Among them, the upper aquiclude of Taiyuan Formation and the Benxi Formation aquiclude are characterized by limited thickness and moderate impermeability, while the lower aquiclude of Taiyuan Formation exhibit significant thickness, superior impermeability and high compressive strength. The hydraulic connection between C₃I and C₃II aquifers is close, while the hydraulic connection between C₃III and Ordovician karst aquifers is close. Based on the impermeability of aquiclude and the water yield property, permeability, drainability, and hydraulic connection of the aquifer, the karst aquifer system beneath the lower coal group is reconstructed to form a ternary karst aquifer system consisting of the C₃Ⅰ—C₃Ⅱ aquifer, the lower aquiclude of Taiyuan Formation, and the C₃Ⅲ—Ordovician aquifer. The C₃Ⅰ—C₃Ⅱ aquifer is drainable, and dewatering and depressurization serves as an effective method for prevention and control karst water disaster, whereas the C₃Ⅲ—Ordovician aquifer, characterized by abundant recharge and low drainability, requires ground regional treatment engineering for karst water disaster prevention and control. The C₃Ⅱ limestone serves as a favorable stratum for ground regional treatment engineering to prevent and control karst water disasters in the C₃Ⅲ—Ordovician aquifer. By investigating and treating the vertical water-conducting channels within the C₃Ⅱ limestone, the water-inrush pathways from the C₃Ⅲ—Ordovician aquifer can be effectively blocked, thereby decoupling the engineering treatment stratum (C₃Ⅱ) from the prevention target stratum (C₃Ⅲ—Ordovician). Based on the barrier effect of the lower aquiclude of Taiyuan Formation, a “source-specific prevention and control” system for karst water disasters is established: Using the lower aquiclude of Taiyuan Formation as an isolation stratum, dewatering and depressurization is applied to the upper composite aquifer (C₃Ⅰ—C₃Ⅱ aquifer), while ground regional treatment engineering is prioritized for the lower composite aquifer (C₃Ⅲ—Ordovician aquifer).