Gas gushing and the co-mining of coal and gas outbursts are common disasters in coal mines. The weakening of thick–hard main roof fracturing can effectively alleviate the gas overrun in the initial mining stage. Four numerical simulation schemes were designed to determine the optimal fracturing treatment scheme for the gas overrun problem in the initial mining stage of the 6505# working face in the Huanghou Coal Mine. Compared with the scheme of the non-fracturing main roof, the weakening of the main roof fracturing could alleviate the concentration of advanced abutment stress. The fissure ratio of the overburden was solved by the binary method, and the dominant channels of gas migration and their morphological evolution under different fracturing schemes were obtained. On this basis, the permeability model of “permeability–fissure ratio–fractal dimension” was established. The results show that the overburden fracture network of the horizontal fracturing scheme has a larger fractal dimension, indicating that the overburden fracture under the scheme is more fully developed and more conducive to gas migration. The research results provide valuable reference for the design of the gas extraction scheme.

In China, groundwater loss caused by underground coal mining is becoming increasingly serious. The key to groundwater restoration is to repair mining-induced water-conducting fractures (WCFs) in the overlying strata. In this study, the adsorption–consolidation sealing characteristics of chemical precipitates were used to conduct permeability reduction (PR) experiments, including adding mixed CaCO₃ and Fe(OH)₃ to a sandstone specimen with a single fracture at room temperature. An aqueous solution of Na₂CO₃ was used as the simulated groundwater, and a solution of mixed CaCl₂ and FeCl₂ was used as the repair reagent to simulate the water seepage conditions of a fractured rock mass. The two aqueous solutions were simultaneously injected into a single-fractured rock specimen at a constant flow rate. The experimental results show that the Fe(OH)₃ colloid encapsulated CaCO₃ crystals in a mixed precipitate, reducing the overall structural stability of the mixed precipitate and restricting repair and PR efficiency. However, the Fe(OH)₃ precipitate had better PR efficiency in the initial stage of the experiment. Therefore, a better scheme was put forward to repair the WCF, utilizing a mixed Fe(OH)₃ and CaCO₃ precipitate with a molar ratio close to 1:4 in the early stage and a single CaCO₃ precipitate in the later stage.