## 2 Transparent Geotechnical Test
### Test Schemes and Process  
In this test, the thickness of the soil interlayer between the new tunnel and the two existing tunnels was chosen as the primary influencing factor, while also considering the tunnel footage for the model test of transparent geotechnical tunnel excavation. The test was conducted on three groups of models under different operating conditions. By adjusting the placement of the existing tunnels and varying the thickness of the soil interlayer, the impact of the new tunnel excavation on the rock surrounding the two adjacent existing tunnels was examined. The specific conditions for the model tests are detailed in Table 2.  
The test process is as follows:  
1. Specim Preparation: A transparent solution of mineral oil was formulated by mixing liquid paraffin and n-tridecane in a weight ratio of 1:0.835. Simultaneously, a certain amount of silica gel powder was prepared. The mixture was then vacuumed to achieve a transparent state.
2. Tunnel Simulation: Two Uli hoses were buried in predetermined positions to represent the existing tunnels.
3. Consolidation: The prepared specimens were consolidated. Once consolidation was complete, weights were applied to simulate the upper load.
4. Photography Setup: A CCD camera was used to capture images. To ensure optimal shooting conditions, lights were arranged next to the camera, and both the lighting and camera focus were adjusted.
5. Excavation: The handle was rotated to simulate the excavation process.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Physical Quantity** & **Value for Silitsone** & **Value for Transparent Material** \\ \hline Gravity \(\gamma\) (kN/m3) & 25.7 & 10.2 \\ Compressive strength \(\sigma_{c}\) (MPa) & 18.5 & 0.037 \\ Internal friction \(\varphi\) (\({}^{\circ}\)) & 34.2 & 0.0684 \\ Cohesion \(c\) (kPa) & 800 & 1.6 \\ Modulus of elasticity \(E\) (MPa) & 2100 & 4.2 \\ Poisson’s ratio \(\mu\) & 0.25 & 0.25 \\ Tensile strength \(\sigma_{t}\) (kPa) & 160 & 0.32 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic physical and mechanical parameters of the material.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Case Number**} & \multicolumn{2}{c}{**Thickness of Interbedded Soil**} & **Excavation** \\ \cline{2-4}  & **Existing Tunnel a (\(I_{1}\))** & **Existing Tunnel b (\(I_{2}\))** & **Footage** \\ \hline
1 & 0.3\(D\) & 0.7\(D\) & 1.9\(D\) \\
2 & 0.3\(D\) & 0.7\(D\) & 2.2\(D\) \\
3 & 0.3\(D\) & 0.7\(D\) & 2.5\(D\) \\
4 & 0.3\(D\) & 0.3\(D\) & 1.9\(D\) \\
5 & 0.3\(D\) & 0.3\(D\) & 2.2\(D\) \\
6 & 0.3\(D\) & 0.3\(D\) & 2.5\(D\) \\
7 & 0.7\(D\) & 0.3\(D\) & 1.9\(D\) \\
8 & 0.7\(D\) & 0.3\(D\) & 2.2\(D\) \\
9 & 0.7\(D\) & 0.3\(D\) & 2.5\(D\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Test schemes.  
This setup allowed for the observation and analysis of the effects of new tunnel excavation on the surrounding rock and existing tunnels.  
The test process is as follows: specimen preparation with liquid paraffin and n-tridecane according to the weight ratio of 1:0.835 formulated into a transparent solution of mineral oil, and at the same time preparing a certain amount of silica gel powder, mixing it, and using a vacuum to achieve a transparent state. In addition, two Uli hoses are buried in an established position in advance to represent the existing tunnel. The configured specimens are consolidated, and after the consolidation is completed, the upper load is applied with weights. The CCD camera is used to take pictures, and in order to achieve the best shooting effect, lights are arranged next to the camera; the light and camera focus are adjusted, and the handle is rotated for excavation.