## 5 The \"Overall-Local\" Coal Burst Prevention and Control Strategy of Isolated Working Face
### Overall Coal Burst Prevention and Control Strategy  
According to the theory of key strata, the primary reason for the local stability and overall instability of the isolated working face is that, with the continuous mining of the working face, the thick and hard key strata above the working face \"hang and remain\", and the stress does not dissipate but rather transfers. The key strata in the suspended state bear the stress of the initially mined coal, which is transmitted to the lower isolated working face, causing the overall supporting stress of the isolated working face to increase. This creates a condition where the overall working face experiences \(\sigma>R\), while certain areas have \(\sigma_{x}<R_{x}\), thus forming the local stability and overall instability of the isolated working face.  
For coal burst types dominated by overall coal burst, pressure relief measures such as roof pre-splitting are usually adopted [37]. Commonly used methods include roof blasting and hydraulic fracturing. Taking roof blasting as an example, this method uses explosives to detonate in the blast hole. The rock mass within a certain range around the blast hole is strongly compressed and crushed, forming a compressed crushing zone. Radial and annular tangential cracks are formed in the crushing and crack zones, interrupting or weakening the transmission of radial and tangential stresses in the surrounding rock [38]. This reduces the stress in the surrounding rock and the energy accumulation in the roof rock layer, as shown in Figure 11. In the figure, \(\theta\) is the inclination angle of the blasting hole (\({}^{\circ}\)). Ls is the borehole depth (m), L\({}_{I}\) is the sealing section (m), and L\({}_{d}\) is the charging section (m). The position of the borehole hole and the final hole should be determined comprehensively based on field conditions, the position of the key stratum, and the position of the blasting rock stratum. The opening position should be arranged near the shoulder and socket of the roadway.  
The main parameters for roof blasting are shown in Table 5 [39; 40]. In the table, the amount of explosives should be determined based on the blasting rock layer, its thickness, and strength. h\({}_{s}\) represents the height difference between the hole opening position and the final hole position (m), l\({}_{s}\) represents the horizontal distance between the hole opening position and the final hole position (m), Q represents the number of explosives, q is the linear charge density of the explosives, and l\({}_{c}\) is the total length of the charge.  
\begin{table}
\begin{tabular}{c c} \hline
**Parameters** & **Values** \\ \hline Drilling depth L\({}_{b}\) & \(\geq\)15 m \\ Drilling diameter R\({}_{b}\) & 100 mm\(-\)200 mm \\ Drilling spacing d\({}_{b}\) & d\({}_{b}\)= k\({}^{\prime}\)d\(\sqrt{1+\frac{1}{R}}\) \\ Drilling lags behind the distance of working face D\({}_{x}\) & 5 m\(-\)20 m \\ Distance between drilling and floor d\({}_{x}\) & 0.5 m\(-\)1.5 m \\ \hline \end{tabular}
\end{table}
Table 4: Main parameters of drilling pressure relief.  
Figure 11: Roof blasting schematic diagram. (**a**) Before roof blasting, (**b**) after roof blasting.  
The frequency of stress relief blasting is typically adjusted based on site-specific conditions, such as stress accumulation levels and the mining progression rate. This dynamic adjustment ensures that stress concentrations are effectively reduced while minimizing risks associated with coal bursts. Although stress relief blasting was not implemented in this study, this method serves as a reference framework for designing and optimizing stress relief measures in similar engineering projects.