## 3 Results
### Analyzing Development and Evolution of Caving and Fracture due to Overburden
#### 3.1.2 Analyzing Development and Evolution of Mining Fractures  
During the mining of the face along the uphill direction, the body of the slope was subjected to the actions of mining and stretching, and cracks appeared on its surface. With the advancement of the working face, fractures between the strata of the main roof gradually developed to the surface of the slope. The evolution of the fracture with the advance of the working face is shown in Figure 14.  
When the working face had advanced 64 m, longitudinal tension-induced fractures appeared ahead of the face and above the open-off cut. Three fractures R1, R2, and R3 are analyzed. The angle between R1 and the coal pillar was 62.6\({}^{\circ}\), the horizontal distance between R2 and the side of the open-off cut was 28.9 m, the boundary angle between R2 and the advancing side was 74.9\({}^{\circ}\), the distance between them was 22.7 m, the angle of fracture R3 was 66.2\({}^{\circ}\), and the crack advanced by 40.3 m.  
When the working face had advanced 104 m, the body of the slope produced fracture R4 with a fracture angle of 70.3\({}^{\circ}\), and an advance fracture distance of 37.7 m. Fractures R2 and R3 developed deep. With the advancement of the working face, fractures formed by mining in the overlying rock became arched. When the working face was pushed to 128 m, the vault of the crack developed to the surface, and then, fracture development was no longer arched. Fracture R4 developed from rock formation S4 to S3, extending from 63.1 to 87.7 m with a width of 8.2 m.  
When the working face had advanced 144 m, the first periodic weighting of the main roof occurred, and mining-induced fractures appeared in the body of the slope periodically. Due to the subsidence of the two strata of the main roof, the width of fractures R2 and R3 increased, and rock mass on both sides of R4 formed a step with a height of 6.9 m.  
When the working face had advanced 172 m, fractures R2, R3, and R4 began to close, and the coal panel was critical (the ratio of width to depth was 1.06). The vertical fracture R5 was produced above the working face, and the angle between R5 and the boundary of the panel was 88.6\({}^{\circ}\), horizontal distance was 3.1 m from the boundary of the panel, and the width of the fissure was 4.5 m.  
When the working face had advanced 188 m, the second periodic weighting of the main roof occurred, R2, R3, and R4 were closed, and R5 widened to 8.7 m. Fracture R6 formed above the working face with a crack angle of 70.3\({}^{\circ}\) and advancing crack distance of 47.3 m.  
When the working face had advanced 212 m, the third periodic weighting of the main roof occurred, and fracture R5 was closed. The depth of R6 increased to 97.1 m and its width to 8 m.  
When the working face had advanced 236 m, the fourth periodic weighting of the main roof occurred, and the surface was characterized by three distinctly fractured rock columns. When the working face had advanced 252 m, the fracture R6 stopped developing. The entire fissure ran through the surface to the bottom of the coal seam, and a new fissure R7 appeared above the working face (top of the slope); the crack angle was 60\({}^{\circ}\), and the advancing crack distance was 85.9 m.  
When the working face had advanced 268 m, the fracture R6 gradually closed, and the width of fracture R7 developed to 2.7 m and its depth to 81.5 m. Because the advance distance was closer to the top of the slope, it intensified the movement of the previously formed step toward the panel, and tensile stress between the step rock mass and the top fracture produced a new vertical fissure R8--its width was 4 m and length was 79.9 m.  
When the working face had advanced 276 m, the mining was stopped and the fractures stopped developing, R8 became 2.8 m wide and 86 m deep, and R7 grew to 5.5 m wide and 106.3 m deep. Finally, the boundary of the panel formed a permanent crack, and the surface of the body of the slope formed a step. Figure 14: Dynamic development of fractures caused by mining.