## 4 Study on Mining Layout Pattern Based on Numerical Simulation
### Unloading and Prevention of Rockburst Measures  
In response to the limited isolation effect of the panel-isolated coal pillar in the current layout pattern of a small panel and a large coal pillar, unloading and prevention of rockburst measures are implemented in the return airway of working face 301 (LW301) in the third panel. The pressure relief is carried out by roof deep hole blasting and large-diameter drilling in the return airway of working face 301 (LW301). The roof deep hole blasting can destroy the structural integrity of the roof above the return airway along the trough side of working face 301 (LW301), preventing the occurrence of large area roof suspension and reducing the lateral abutment pressure exerted on the panel-isolated coal pillar by working face 301 (LW301). The large-diameter drilling in the coal seam causes the coal on both sides of the return airway to break, transferring stress to the deeper part of the surrounding rock of the roadway, reducing the stress concentration in the panel-isolated coal pillar area, ultimately improving the stability of the panel-isolated coal pillar, and further reducing the risk of rockburst [28].  
Figure 15: Plane distribution of microseismic events in the panel-isolated coal pillar area.  
Two blasting hole schemes are used for unloading in the roof above the return airway in working face 301 (LW301): a fan-shaped roof hole in the working face and a down-groove cutting roof hole. For the fan-shaped hole blasting in the working face, a set of three holes (1#, 2#, 3#) is arranged, with hole positions at the shoulder recess on the production side; the distance between blasting holes is 15 or 20 m, the hole diameter is 85 mm, and the sealing length is not less than 15 m. For the cutting roof hole along the groove, a set of two holes (4#, 5#) is arranged; the opening position is the middle part of the roadway roof, the distance between the blasting holes is 5 m, the hole diameter is 85 mm, and the sealing length is not less than 15 m [29]. The specific blasting parameters are shown in Table 2 and Figure 16.  
Large-diameter drilling is arranged in the vertical side of the LW301 return airway, with a hole depth of 30 m, a hole diameter of 150 mm, a sealing length of 3 m, and a hole spacing of 1 m or 2 m, with a distance of 1.2-1.5 m from the floor [30]. The layout of large-diameter coal seam drilling is shown in Figure 17.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Drilling Number** & **Drilling Elevation Angle/(c)** & **Blast Hole Depth/m** &
\begin{tabular}{c} **Explosive** \\ **Dosage/kg** \\ \end{tabular} & **End Hole Position** \\ \hline
1\# & 60 & 62 & 60 & Coarse grain sandstone \\
2\# & 50 & 44 & 40 & Medium grain sandstone \\
3\# & 40 & 32 & 40 & Fine grain sandstone \\
4\# & 60 & 62 & 60 & Coarse grain sandstone \\
5\# & 60 & 38 & 40 & Medium grain sandstone \\ \hline \hline \end{tabular}
\end{table}
Table 2: Roof deep hole blasting parameters.  
Figure 16: Schematic diagram of the layout of the roof deep hole blasting. (**a**) Drill hole layout plan. (**b**) Schematic diagram of I-I section. (**c**) Schematic diagram of II-II section.  
Figure 17: Schematic diagram of the layout of the large-diameter drilling in the coal seam. (**a**) Section diagram. (**b**) Plane diagram.