Evolution and Control of Overburden Fracture in Extra-Thick Coal Seam Mining with Hard Roofs: Ground Grouting Sealing and Case Study

In the process of coal mining, the original state of rock strata is seriously damaged and a large number of fractures are produced. If the fracture is connected to the overlying natural water body, leakage of surface water and ground water will cause serious mine water damage and lack of regional water resources. If the fracture is connected with gob water containing harmful gases and substances, in addition to the occurrence of mine water damage, it will pollute the water body. In the process of mining extra-thick coal seams, water inrush accidents caused by the development of large-space overburden fracture are more frequent, which causes more serious loss and pollution of water, and even desertification of land. In this paper, digital panoramic imaging technology is used to monitor the movement of overburden rock during the mining process. A reasonable time for fracture grouting sealing was proposed based on the similar simulation experiment and the evolution characteristics of fracture fractal dimension and a reasonable ground grouting sealing scheme was designed. The field monitoring results show the grouting effectively seals the fractures and reduce air leakage and solve the risk of gob water leakage above the working face. The research in this paper reveals the evolution characteristics of large-space overburden fractures in extra-thick coal seam mining with hard roofs. It shows that ground grouting sealing is an effective means to reduce the secondary disasters of fracture development, which has practical value and practical significance for environmental protection and coal safety development.