Development of Water-Conducting Fractures in Overlying Strata under Conditions of Thick Unconsolidated Layers and Varying Bedrock Thickness

The Wanfu Coal Mine faces water-sand inrush risks from the Neogene aquifer during coal extraction. This study takes the 1,305 working face as a case and adopts physical modelling and discrete element simulations to investigate overburden fracture development under different geological structures and mining activities. It reveals the critical locations and key periods for preventing water-sand inrush from the aquifer at the bottom of the Neogene system. It was shown that under 20 MPa geostress, as bedrock aquifuge thickness continuously increases, the number of connected fracture zones within the aquifuge gradually decreases, and their locations shift toward the ends of the working face along the strike. The ends of the working face along the strike are critical areas for preventing water-sand inrush. When bedrock aquifuge thickness reaches 24 m, it can block the hydraulic connection between the water-conducting fractures and the Neogene aquifer, suppressing the upward expansion of the water-conducting channels.