Abstract:
As coal resources continue to be depleted, mining faces are gradually extending to deeper levels, where they are confronted with complex geological conditions such as high-pressure confined water and high in-situ stress, leading to an increasing risk of roof water inrush. Water-conducting fractures are among the primary channels through which mining-induced roof water inrush occurs, posing significant threats to the safety of coal mine operations. As a major Carboniferous–Permian coal-bearing area in North China, Hanxing Mining Area is severely affected by Ordovician karst water inrush during deep mining activities. Accurate prediction of the development height of the water-conducting fractured zone (WCFZ) is essential for the prevention and control of roof water disasters in coal seams. Taking the north shaft of Dongpang Mine in Hanxing Mining Area as the study area, a method is proposed based on the variation of permeability coefficient along boreholes to determine the development height of the WCFZ, that is the double-end sealing water injection method is used to reflect the development degree of overburden fractures by observing water loss at different borehole depths, thus allowing for the estimation of the spatial extent of the WCFZ. This method is verified by integrating “borehole camera” observation, theoretical calculation, and numerical simulation to analyze the development characteristics of mining-induced fractures in the No. 9 coal seam and to conduct a prediction of the WCFZ height. The results indicate that the roof strata undergo structural failure under mining-induced disturbance. The fracture development process can be divided into four stages: “initial development, slow growth, rapid expansion, and stable equilibrium”, ultimately forming a stable caving structure. The predicted height of the caving zone ranges from 26 m to 31.91 m, with a caving ratio of 3.84–5.32; the predicted WCFZ height ranges from 82.58 m to 96.52 m, with a fracturing ratio of 13.76–14.26. The permeability coefficients obtained from borehole observations exhibit distinct segmental variations at different depths, which correspond closely to the fracture zones revealed by “borehole camera” inspection. The abrupt changes in permeability are generally consistent with the termination boundaries of the fractures, indicating that this method can effectively reflect the spatial distribution characteristics of the WCFZ.