## 4 Numerical Simulation of Water-Flowing Fracture Zone in the Working Face  
As can be seen from the simulation results of the above five schemes, the development of separation layer in the working face is basically lower than KS4. Accordingly, in order to analyze further the development of water-flowing fracture zone in the working face, all the rock formations above KS4 are ignored, and all the rock formations between the coal seam and KS4 are modeled with actual lithology based on the original model, and a uniform load of 11.2 MPa is loaded on KS4. The length and width of the model is 1600 m and 800 m, respectively, and the height is equal to that of KS4. In order to be consistent with the actual mining conditions of the working face, the mining height of the model is set to be 5 m, and the mining width is 300 m.  
[PERSON] conducted a three-dimensional numerical simulation on the overburden failure in the working face and found that when the shear stress reaches its peak value and exceeds the maximum shear strength of the rock mass, fractures will be generated in the rock mass [22]. With reference to this finding, this study attempted to use the shear displacement in the simulation process to visually represent the mining-induced fractures. In order to simulate the development of the water-flowing fracture zone after mining and quantitatively grasp its development height, the joint shear displacement in 3 DEC software was used to represent the fracture. After the excavation of the model, the element block is hidden by setting parameters, and only the joint shear displacement in the model  
Figure 14: Variation curves of separation layer at different mining heights and widths: (**a**) Variation curves of separation layer at different mining heights; (**b**) Variation curves of separation layer at different mining widths. Figure 15: Stress concentration coefficient and subsidence curves at different mining heights and widths: (**a**) Different mining heights; (**b**) Different mining widths. is displayed, and the corresponding displacement cloud diagram is obtained (shown in Figure 16). Due to the influence of mining, the penetration height of joint shear displacement in each model is different under different excavation conditions. By comparing the joint shear displacement cloud diagrams under various conditions, the maximum penetration height of the joint shear displacement in the cloud diagram is measured. Then, with the thickness of coal seam and floor in the model subtracted, the development height of the water-flowing fracture zone can be obtained (Equation (1)). The measurements are conducted three times, and the calculation results are averaged. In this way, the height of the water-flowing fracture zone of the model can be roughly obtained. \[H_{w}=MAX\{h_{i}\}+\Delta h-h_{c}-h_{f} \tag{1}\]  
where \(H_{w}\) denotes the height of water-flowing fracture zone, m; \(h_{i}\) refers to the measurement height of joint shear displacement under certain mining condition; \(i\) represents some certain mining condition (the working face is excavated for \(i\) m), and its value is 0, 50, 100,..., and its unit is m. \(\Delta h\) denotes the possible penetration fracture thickness between overlying strata with a height lager than \(h_{i}\) in the goat area behind the working face, and its unit is m. \(h_{c}\) denotes the thickness of coal seam in the model, and its unit is m. \(h_{f}\) represents the thickness of coal seam floor, and its unit is m as well. The simulation of water-flowing fracture zone under different advancing states of working face is shown in Figure 17.  
Through observation, it is found that when the model is excavated to 700 m, the sufficient conditions for mining in the working face are satisfied, and the water-flowing fracture development is clear and remarkable. The cloud diagram of the strike of the water-flowing fracture zone under this advancing distance is selected (Figure 18), and the maximum height of the water-flowing fracture zone of the model is calculated in combination with Equation (1).