## 3 Analysis of Pressure Relief Effect of Cutting Top Parameters
### Pressure Relief Effect of Different Top Cutting Parameters
#### 3.2.2 Pressure Relief Effect of Roof-Cutting Angle  
The roof-cutting height was controlled to 9 m, the roof-cutting angle parameters were increased to 70\({}^{\circ}\) and 90\({}^{\circ}\), respectively, and the pressure relief effect of the left roadway roof was analyzed under different roof-cutting angles. The distribution of maximum and minimum principal stresses at 9 m of the roadway roof under different cutting angles is shown in Figure 6.  
Under different roof-cutting angles, the distribution of maximum principal stress on the roof of the advanced working face roadway showed little variation, indicating that the pressure relief effect was not significant under different roof-cutting angles, as shown in Figure 6a. The variation pattern of the maximum principal stress on the top plate of the roadway with different top-cutting angles in the lagging working face was similar, and the difference was significant. At a distance of 60 m from the lagging working  
Figure 5: Variation curve of stress of the roadway roof: (**a**) Maximum principal stress of the roadway roof. (**b**) Minimum principal stress of the roadway roof.  
Figure 6: Distribution curve of stress of the roadway strike roof: (**a**) Maximum principal stress of the roadway roof. (**b**) Minimum principal stress of the roadway roof.  
face, the maximum principal stress at a roof-cutting angle of 80\({}^{\circ}\) was 3.3 MPa, which was 0.5 MPa and 1.9 MPa lower than the 3.8 MPa and 5.2 MPa at a roof-cutting angle of 70\({}^{\circ}\) and 90\({}^{\circ}\), respectively.  
Figure 6b reflects the minimum principal stress distribution of the roof of the roadway with different cutting angles in front of the working face. The influence of different roof-cutting angles on the distribution of minimum principal stress in the advanced working face was relatively small, whereas the variation of minimum principal stress in the lagging working face was relatively large. This is manifested in the range of 10 m to 60 m in the lagging working face. The minimum principal stress in the roof plate of the retained roadway at different roof-cutting angles showed a fluctuating pattern. When the roof cutting angle was 80\({}^{\circ}\), the minimum principal stress in the roof plate of the retained roadway was 12.8 MPa, which was 2.2 MPa and 3.7 MPa lower than that at 70\({}^{\circ}\) and 90\({}^{\circ}\), respectively.  
Based on the distribution patterns of maximum and minimum principal stresses on the roof of the retained roadway under different cutting heights and angles, it can be concluded that when the cutting angle is 80\({}^{\circ}\), the pressure relief effect of the retained roadway roof is significantly better than that of the cutting angles of 70\({}^{\circ}\) and 90\({}^{\circ}\). The quality of the pressure relief effect directly affects the difficulty of maintaining the roadway roof. Taking the 7135 working face of Qidong Coal Mine as the engineering background, when the cutting height is 9 m and the cutting angle is 80 \({}^{\circ}\), the pressure relief effect of the roadway roof is most obvious, and the concentration of mining stress on the left roadway roof is the smallest, which is more conducive to the maintenance of the roadway roof.