## 2 Background Overview
### Monitoring Results and Analysis  
According to the similarity laws, relevant site parameters were converted, resulting in an equivalent tunnel radius of \(\alpha\) = 0.0342 m and an initial ground stress of \(P_{0}\) = 156 kPa. Mechanical tests on the similar materials for coal yielded an elastic modulus E = 3.21 GPa, a Poisson's ratio of 0.35, an expansion coefficient of the fracture zone of 1.4, an internal friction angle of 27.83\({}^{\circ}\), and a residual cohesion of 0.624 MPa. These parameters were substituted into theoretical formulas for calculations, and the radial strain at the boundary between the elastic and plastic zones of the section coal pillar was determined to be 560 \(\mu\)e, while the radial strain at the boundary between the fracture zone and the plastic zone was determined to be 1040 \(\mu\)e. These values served as reference points for analyzing the distribution characteristics of the elastic-plastic regions of the coal pillar strain monitored by the Fiber Bragg Gratings (FBGs). \[\begin{cases}\mu_{e}=\frac{1+\mu}{E}\Big{[}(1-2\mu)P_{0}r+(P_{0}-\sigma_{r} \Big{|}r=R_{s})\frac{R_{s}^{2}}{r}\Big{]}\\ \varepsilon_{re}=\frac{1+\mu}{E}\Big{[}(1-2\mu)P_{0}-(P_{0}-\sigma_{r}\Big{|  
\[ \begin{cases}\varepsilon_{rb}=-\frac{1+\mu}{E}(P_{0}-\sigma_{r}|r=R_{s})\,\eta_{b} \Big{[}\frac{\eta_{s}-1}{\eta_{s}+1}-\frac{2}{\eta_{s}+1}(\frac{R_{s}}{R_{b}})^{ 1+\eta_{s}}\Big{]}(\frac{R_{b}}{r})^{1+\eta_{s}}\\ \varepsilon_{gb}=\frac{1+\mu}{E}(P_{0}-\sigma_{r}|r=R_{b})\,\Big{[}\frac{\eta_ {s}-1}{\eta_{s}+1}-\frac{2}{\eta_{s}+1}(\frac{R_{s}}{R_{b}})^{1+\eta_{s}}\Big{]} (\frac{R_{b}}{r})^{1+\eta_{s}}\end{cases}  \tag{3}\]  
Figure 6 shows the deformation monitoring results of the 5-1# section coal pillar from 9 July to 29 July, based on monitoring points 1-9 from five FBG boreholes. The strain variation curve at monitoring points 1-9 in borehole 1 shows that with the advancement of the working face, the strain near the 22,208 working face rapidly increased due to the impact of mining stress on the underlying coal seam working face. The stress concentration effect gradually increased within about 10 m in front of the working face. Subsequently, the strain curve quickly decreased, indicating that the 5-1# section coal pillar was affected by the concentrated stress of the overlying oblique residual coal pillars. The deformation influence range was from the monitoring points 5 to 9 on the left side at 12.5 m, while there was almost no noticeable change in the range from monitoring points 1 to 4, differing from the strain variation patterns under vertical or parallel conditions of the overlying and underlying coal pillars. The strain variation curve at monitoring points 1-9 in borehole 2 showed a steep increase in strain with the advancement of the working face. However, due to issues arising during actual construction, the monitoring point in borehole 2 broke about 5 m before the 22,208 working face reached the borehole opening, resulting in abnormal data collection. Given the bell-shaped load distribution of the 5-1# section coal pillar, the strain variation trend at borehole 4, which symmetrically aligns with borehole 2, was used for reference. Figure 6: _Cont._  
As the 22,208 working face advanced, the 5-1# section coal pillar was influenced by the advanced support pressure and lateral support pressure. The strain curves measured by the nine monitoring points in borehole 5 showed a sharp increase approximately 100 m from the coal wall. Using the theoretical values to analyze the elastic-plastic zoning range within the coal pillar width, the monitoring points 8 and 9 reached the plastic zone approximately 178 m from the borehole opening.