## 6 Conclusions  
FLAC3D numerical simulation was used to study the influence of vertical stress, deformation, and support structure under different parameters of variable diameter pressure relief boreholes, and the following main conclusions were drawn:  
1. Shallow borehole diameter has less influence on stress transfer and more influence on roadway deformation and support structure. When the shallow borehole diameter increases, the deformation of the roadway becomes larger, and the effective binding force of the anchor decreases, which is easy to cause the de-anchoring phenomenon. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Measuring Point Depth** & **Warning Level** & **Warning Value** \\ \hline Shallow hole (8 m) & Intermediate warning & 10–12 MPa \\ Advanced warning & \(\geq\)12 MPa \\ \hline Deep hole (15 m) & Intermediate warning & 12–14 MPa \\ Advanced warning & \(\geq\)14 MPa \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Stress online monitoring and early warning criteria. Figure 17: Stress change curve of 19,111 auxiliary roadway. 2. The deep borehole diameter has a greater influence on stress transfer and a smaller influence on roadway deformation and support structure. The larger the deep borehole diameter, the smaller the change of surrounding rock stress and effective binding force of the anchor, but the pressure relief zone formed in the deep part of the borehole continues to increase. And the effect of roadway stress transfer is better. 3. The influence of variable borehole diameter position on stress transfer, roadway deformation, and anchor support is larger. With variable aperture position in the anchorage area, the stress transfer effect is better, but the roadway deformation is larger, and the effective binding force of the anchor is smaller. With variable aperture position between the anchorage area and the peak stress position of the roadway side, the stress transfer effect is better, and the deformation of the roadway is smaller, the effective binding force of the anchor is reduced to a lesser extent. With variable aperture position outside the peak stress position of the roadway side, although the deformation of the roadway is reduced, the effective binding force of the anchor is also small, but the stress transfer effect is better. Although the deformation of the roadway is reduced, the change of the effective binding force of the anchors is also small, but the effect of stress transfer is poor. 4. Borehole spacing has a significant effect on the stress transfer to the surrounding rock, the deformation of the roadway, and the impact of anchor support. When the borehole spacing is larger than 2.0 m, the effect of vertical stress transfer is poor. When the borehole spacing is between 1.0 m and 2.0 m, the vertical stress begins to transfer to the depth of the surrounding rock, the deformation of the roadway is small, and the effective constraint force of the anchors can be maintained at the normal level. When the borehole spacing is smaller than 1.0 m, the deformation of the roadway is larger, and the effective binding force of the anchors decreases sharply. 5. The variable diameter drilling program is given, and variable diameter boreholes are constructed within 200 m of the working face. The boreholes are arranged in a single row, 1.5 m away from the floor, with a spacing of 2.0 m. The depth of the holes on the coal wall side is 16 m, the depth of the holes on the coal pillar side is 12 m, the diameter of the shallow boreholes is 100 mm, and the diameter of the deep boreholes is 250 mm; the position of the variable diameter boreholes is located in the place of 4 m away from roadway side. The industrial test was carried out in the 19,111 auxiliary transport roadway of the Pingshuo No.1 Coal Mine. Through the method of drilling bits and the monitoring of the drilling stress gauge, the stress concentration of the surrounding rock in the roadway is reduced, which proves that the variable diameter drilling pressure relief program is reasonable and feasible. L.T.