## 2 Experimental Outline
### Experimental Scheme  
The design of the model test study program takes into account the tunnel burial depth and the lateral pressure coefficient, which are significant parameters that impact the stress and deformation time-dependent characteristics of the surrounding rock and lining structure. Based on the investigation and design data of the dependent project, the burial depth and lateral pressure coefficient values were determined for the test. Table 4 illustrates how the test conditions are set up. Three conditions for the tunnel burial depth--15, 30, and 45 m--and two types of coefficients for the lateral pressure coefficient--0.3 and 0.5--are chosen.  
Figure 3: Layout of the data acquisition system.  
The lateral pressure is maintained constant in working conditions 1-3, and a graded loading mode is used to mimic the variation in tunnel burial depth by varying the loading in the vertical direction. This allows for the study of the impact of burial depth on the time-dependent characteristics of surrounding rock and lining stress and deformation. To study the influence of the lateral pressure coefficient on the time-dependent characteristics of surrounding rock and lining stress and deformation, working conditions 4 and 5 are established, and the graded loading mode is used to simulate the change in lateral pressure coefficient by varying the loading load in the horizontal direction. The loading cycle of each stage of the graded loading mode is set to 8 days because pre-experimental data indicate that the changes in stress and deformation characteristics of the surrounding rock and lining structure after 8 days of loading are very minimal.  
The main test steps are as follows: (1) calculating and evaluating the quality of each component material, mixing the materials, and placing the resulting surrounding rock-like material in the model box; (2) creating the tunnel lining structure and burying it as indicated in Figure 4 when the test filler reaches the tunnel's height; (3) installing the data acquisition system in accordance with the test program; (4) waiting for the model to finish laying the overall model before performing the overall maintenance; and (5) following the completion of the maintenance, executing the constant pressure loading test in accordance with the predetermined test program.  
The weak surrounding rock creates a creep effect under environmental pressures during the long-term operation of tunnels, which impacts the long-term operating safety of tunnels by resulting in complicated time-dependent evolutionary patterns of stress and deformation in the surrounding rock and lining. Test group 1 was initially chosen to track changes in the stress of the surrounding rock, the internal force and displacement of the lining structure, and the contact force between the surrounding rock and lining structure in order to analyze the time-dependent evolutionary patterns of stress and deformation of the surrounding rock and lining structure.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Condition** & **Simulated** & **Vertical** & **Lateral Pressure** & **Lateral** \\
**Number** & **Burial Depth/m** & **Load/kPa** & **Coefficient** & **Load/kPa** \\ \hline
1 & 15 & 17 & 0.3 & 5.1 \\
2 & 30 & 31 & 0.3 & 9.3 \\
3 & 45 & 45 & 0.3 & 13.5 \\
4 & 15 & 17 & 0.5 & 8.5 \\
5 & 30 & 31 & 0.5 & 15.5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Test conditions.  
Figure 4: Pre-embedding of tunnel lining structure.