Evolution Analysis of Thick and Hard Overburden Strata and Water-Conducting Fractured Zone in Fully Mechanized Top Coal Caving Working Face

According to the caving law of thick and hard overlying strata and the evolution characteristics of water-conducting fracture zone, comprehensive analysis of the collapse characteristics of the thick and hard overburden in the fully mechanized caving face, the information on the internal structure of the overburden strata and the development of the "two zones" of the overburden strata after the coal seam in the working face was carried out using methods of similar simulation experiment, microseismic monitoring system, numerical simulation, theoretical analysis and engineering practice combined research methods. Comprehensive analysis of the collapse characteristics of the thick and hard overburden strata in the fully mechanized caving face, the information on the internal structure of the overburden and the development of the "two zones" of the overburden strata after the coal seam in the working face. The results show that: the height of the overburden collapse envelope increases with the advancement of the working face. When fully mined, the collapse height of the overburden is stable, and the height of the water-conducting fracture zone ranges from 100m to 120m. The height is consistent with the overburden collapse envelope. Most of the microseismic events occur near the water-conducting fracture zone, where the energy density is concentrated to form the water-conducting fracture zone. In the numerical simulation, the concentrated distribution area of the fissure field presents a "bridge arch" type of distribution. The fissure development model in the middle of the goaf is higher than the ends of the working face, and the roof rock formation is obviously deformed. When the energy value of the microseismic event reaches 108.708J, a crack will occur, and the crack will gradually penetrate to form a water-conducting fracture zone. Engineering practice verifies that the height range of the water-conducting fissure zone is determined to be 98m-123m. The caving of the thick hard overburden strata and the evolution of the water-conducting fissure zone provide a scientific basis for the prevention and control of water in the working face.