## 5 Experimental Data Analysis
### Bottom Pressure Sensor Data Analysis  
The model's base is equipped with 24 pressure sensors, numbered sequentially from right to left as 1, 2, 3, \(\ldots\), 23, and 24. Each sensor measures 5 cm in width, effectively covering the entire bottom of the model. Using the 108-channel pressure data acquisition system, data from the bottom sensors were recorded before and after loading the model. After analyzing the data following 20 loading cycles, pressure variation curves for the sensors were plotted, as shown in Figure 11.  
From the above Figure 11, it can be observed that the pressure changes were greatest at Sensor 5, located 37.5 cm from the centerline on the left side, with a variation of 184.16 kPa, and at Sensor 20, located the same distance from the centerline on the right side, with a change of 176.52 kPa, as shown in Table 4. In contrast, the pressure variation was minimal at Sensor 13, situated at the center, which decreased by only 7.772 kPa. This indicates that the peak pressure support area for the opening cut is located 16 cm from each side, where the surrounding rock is particularly susceptible to failure, potentially leading to spalling of the opening cut. This observation aligns with the significant damage observed at the sides of the model, where the loosened areas reached 9.3 cm and 8.1 cm, respectively. The peak pressure support area, located 16 cm from each side, highlights the regions most susceptible to failure. These findings are crucial for optimizing support designs to target high-stress areas.  
To analyze the variation in individual sensors, representative pressure variation values from the right-side Sensors 5, 8, 9, and 13 were selected. The pressure change curves for each loading cycle are plotted in Figure 12.  
Analysis of Figure 12 reveals that the pressure on Sensor 5, located 37.5 cm from the centerline, is significantly greater than that of the other three sensors. In contrast, the pressure recorded by Sensor 9, located beneath the opening cut, is noticeably lower than that of Sensor 8, which is situated beneath the left side of the opening cut. The sensor directly under the center of the opening cut experiences the least pressure. During the  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline Sensor number & 5 & 8 & 9 & 13 & 16 & 17 & 20 \\ \hline Distance from centerline/cm & 1.12 & 0.693 & 0.663 & \(-2.83\) & \(-2.12\) & \(-0.56\) & 0.92 \\ \hline Pressure variation/kPa & 184.16 & 50.23 & 33.01 & \(-7.771\) & 18.28 & 37.57 & 176.52 \\ \hline \end{tabular}
\end{table}
Table 4: Main pressure variation values of bottom sensors.  
Figure 11: Twenty-four bottom pressure sensors’ variation curves during loading.  
Figure 12: Main pressure sensor variation curves.  
first 13 loading cycles, the pressure changes for Sensors 5, 8, and 9 exhibit a gradual and linear increase. However, after the 14 th loading cycle, the deterioration of the coal walls on both sides of the opening cut accelerates, leading to an increase in the loosened area. As a result, the pressure variations for Sensors 8 and 9 decrease with continued loading, while the pressure variation for Sensor 5 increases. This change occurs because the coal walls near the opening cut become damaged and loose, losing their ability to support the overlying rock layers. Consequently, the rock mass farther from the coal walls starts to take on the main load-bearing role. As loading increases, this further expands the loosened area of the coal walls, ultimately leading to widespread spalling.