## 3 Materials and Methodology
### Construction of the Physical Analog Model
#### 3.1.1 Displacement Monitoring Design  
To monitor the displacement of the entire model, MatchID-2D was used, which is a non-contact full-field displacement and strain measurement device. This system consists of a MatchID image capture setup, a 12-megapixel high-resolution camera that measures, in a 2D field of view, the displacement and strain, with a measuring range of 0.01 pixels and 0.001% accurate. To provide a clear background for monitoring, the model's surface was colored white. Afterward, many black spots were drawn on the model's surface to track displacement, as illustrated in Figure 3. MatchID tracked these spots across multiple  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**N**} & \multirow{2}{*}{**Lithology**} & \multicolumn{2}{c}{**Thickness**} & \multicolumn{2}{c}{**Total Dry**} & \multirow{2}{*}{**m1**} & \multirow{2}{*}{**m2**} & \multirow{2}{*}{**m3**} & \multirow{2}{*}{**m4**} \\ \cline{3-3} \cline{5-8}  & & **Real (m)** & **Model (m)** & & & & & \\ \hline
1 & Fine-grained sandstone & 5 & 5 & 67.52 & 57.86 & 6.76 & 2.90 & 7.50 \\ \hline
2 & Mudstone & 4 & 4 & 54 & 47.24 & 4.72 & 2.04 & 6.3 \\ \hline
3 & Sandy mudstone & 5 & 5 & 67.52 & 57.86 & 6.76 & 2.90 & 7.50 \\ \hline
4 & Medium-grained sandstone & 11 & 11 & 162.04 & 129.6 & 22.7 & 9.74 & 18 \\ \hline
5 & Sandy mudstone & 14 & 14 & 189.04 & 151.2 & 26.48 & 11.36 & 21.02 \\ \hline
6 & Medium-grained sandstone & 6 & 6 & 81.02 & 64.80 & 11.35 & 4.87 & 9.00 \\ \hline
7 & Mudstone & 3 & 3 & 40.5 & 35.44 & 3.54 & 1.52 & 4.75 \\ \hline
8 & Medium-grained sandstone & 28 & 28 & 378.08 & 302.4 & 52.96 & 22.72 & 42.04 \\ \hline
9 & Sandy mudstone & 6 & 6 & 81.02 & 64.80 & 11.35 & 4.87 & 9.00 \\ \hline
10 & Fine-grained sandstone & 2 & 2 & 27 & 23.62 & 2.36 & 1.02 & 3.15 \\ \hline
11 & Sandy mudstone & 4 & 4 & 54 & 47.25 & 4.72 & 2.03 & 5.20 \\ \hline
12 & 4 th coal seam & 1.5 & 1.5 & 20.25 & 17.72 & 1.77 & 0.76 & 2.38 \\ \hline
13 & Fine-grained sandstone & 4 & 4 & 54 & 47.25 & 4.72 & 2.03 & 5.20 \\ \hline
14 & Sandy mudstone & 5 & 5 & 67.52 & 57.86 & 6.76 & 2.90 & 7.50 \\ \hline
15 & Fine-grained sandstone & 3 & 3 & 40.5 & 35.44 & 3.54 & 1.52 & 4.75 \\ \hline
16 & Mudstone & 3 & 3 & 40.5 & 35.44 & 3.54 & 1.52 & 4.75 \\ \hline
17 & Fine-grained sandstone & 6 & 6 & 81.02 & 64.80 & 11.35 & 4.87 & 9.00 \\ \hline
18 & Sandstone & 18 & 18 & 242.98 & 208.2 & 24.34 & 10.44 & 27 \\ \hline
19 & Mudstone & 6 & 6 & 81.02 & 64.80 & 11.35 & 4.87 & 9.00 \\ \hline
20 & 5 th coal seam & 2.5 & 2.5 & 33.76 & 28.93 & 3.38 & 1.45 & 3.75 \\ \hline
21 & Mudstone & 2 & 2 & 27 & 23.62 & 2.36 & 1.02 & 3.15 \\ \hline
22 & Fine-grained sandstone & 7 & 7 & 94.52 & 75.60 & 13.24 & 5.68 & 10.51 \\ \hline
23 & Mudstone & 4 & 4 & 54 & 47.24 & 4.72 & 2.04 & 6.3 \\ \hline \hline \end{tabular}  
* NB: m1 represents the mass of river sand, m2 the mass of calcium carbonate, m3 the mass of gypsum, and m4 the mass of water.  
\end{table}
Table 3: Mechanical parameters of the physical simulation model.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Stratum** & **Compressive Stress (MPa)** & **Simulate Stress (KPa)** \\ \hline Medium-grained sandstone & 21 & 93 \\ Fine-grained sandstone & 54 & 162 \\ Sandy mudstone & 25 & 75 \\ Mudstone & 20.27 & 60.87 \\ Sandstone & 17 & 51 \\
5 th coal seam & 9.73 & 29.22 \\ Fine sandstone & 38.91 & 116.85 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The proportions of the materials used for the physical similarity model.  
images to calculate displacements. By analyzing images from the high-resolution camera, MatchID determined the displacements between these marked points. When these spots are too close or connected to each other, it can confuse the software, reduce resolution, and affect the accuracy of the results. Excessive rotation can complicate the tracking and indicate of out-of-plane motion. The spots' deformation can have an impact, emphasizing the importance of accurate calibration, strain measurement, and pattern application.