###### Abstract  
To study the cavity of thick hard overburdens and evolution of water-conducting fracture zones in fully mechanized top-coal cavity faces of gently inclined extra-thick coal seams, we comprehensively analyzed the 8103 working face of the Beixinyao Coal Mine. We investigated to the saving characteristics of thick hard overburden in fully mechanized top-coal caving faces, fracture information of the internal structure of overburden, and development heights of the \"two zones\" of overburden after coal mining. Our research methods included those of similarity simulation experiments, such as the use of microseismic monitoring systems, numerical simulations, theoretical analysis, and engineering practice. The results showed that the overlying strata generally experienced stages of roof caving, crack formation, delamination, crack development, and surface subsidence. Due to the influence of overlying strata movement and mining, the separation layer experienced an evolution process called \"emergence-development-closure\", where the height of the overlying strata caving envelope increases with the advancing of the working face. When full mining was achieved, the overlying strata caving height was stable, and the height development range of the water-conducting fracture zone was 100-120 m, which is consistent with the height of the overlying strata caving envelope. Most microseismic events occurred near the water-conducting fracture zone, and the water-conducting fracture zone was formed in an area with concentrated energy density. In our numerical simulation, the concentrated distribution area of the fracture field was characterized by a \"bridge arch\". The fracture development model in the middle of the goat was higher than at both ends of the working face, and roof strata deformation was obvious. When the energy value of microseismic event reaches 108.708 J, cracks are produced, and these cracks gradually penetrate to form water-conducting fracture zones. Engineering practice showed that the height range of the water-conducting fracture zone was 98-123 m, and caving of the thick hard overburden and evolution of the water-conducting fracture zone in a fully mechanized top-coal cavity face provide a scientific basis for water prevention and control. overlying strata caving; microseismic monitoring; water-conducting fracture zone; numerical simulation +
Footnote †: journal: Applied Sciences  
of the overburden under specific mining conditions. [PERSON] et al. [11] analyzed the relationship between the height of water-conducting fracture zone development and various influencing factors. [PERSON] et al. [12] argued that different structural stabilities of the main key stratum would lead to different forms of water-conducting fractures in the upper part of the main key stratum. [PERSON] et al. [13] investigated the development of water-conducting fracture zones using borehole TV combined with a simple hydrological observation method. [PERSON] et al. [14] observed the development of water-conducting fracture zones by combining theoretical calculations with field measurements. [PERSON] [15] measured the characteristics of water conduction in overlying strata fissures and fissures in the working face through the changes of overlying strata in fully mechanized top-coal caving mining. Many scholars have studied the laws of fracture development caused by coal seam mining and other influencing factors. However, the existing research focuses on theoretical analysis. We use various methods of physical and numerical simulations for a comprehensive understanding of the development of overlying rock fractures and conduct field verification. A water-conducting fracture zone is formed due to a water inrush phenomenon caused by the collapse of overlying strata in the mining face [16]. The height of the water-conducting fracture zone is affected by many factors, including coal seam buried depth, coal seam dip angle, working face width, coal seam thickness, physical and mechanical properties of coal rock, etc.