# Centrifuge Modelling of the Impact of Excavation with Partition Piles on Adjacent Existing Tunnel
## 2 Design of the Centrifuge Modelling
### Model Preparation
#### 2.2.2 Arrangement of Structural Components  
In the model, all structural members of the test were embedded in the soil layer during the preparation of the foundation and were organized along the width bearing of the model box to more fully simulate the two-dimensional state. To ensure the precision of the verticality of the retaining walls and partition walls, the corresponding wall support structure was used during the foundation preparation process. After the walls were fixed, the preparation of the sand soil foundation was carried out in sections. To minimize friction, EVA sponge tape was attached, and Vaseline was applied along the edges of the structure on both sides. For the materials used in the experiment, the structural components were made of innovative magnesium-aluminum alloy material. The material density was 1.78 g/cm\({}^{3}\). And its elastic modulus was approximately 40 GPa, which was very close to the elastic modulus of actual concrete materials [41]. Therefore, the dimensions of the structural components in the model could be determined based on the geometric similarity ratio. During the trial, a partition wall was utilized to mimic the piles, and the methodology for assessing wall thickness was derived from considerations of equivalent bending stiffness. Furthermore, the experimental setup incorporated substantial modifications to the partition wall configurations, introducing a distinctive dimension to the overall procedure. The partition piles had a diameter of 8 mm (prototype: 400 mm), and their spacing was 12 mm (prototype: 600 mm). By calculating the equivalent bending stiffness, the thickness of the partition wall was 6 mm (prototype: 300 mm). Furthermore, the specific geometric parameters of the partition wall, retaining wall, and tunnel structure are shown in Table 3.  
\begin{table}
\begin{tabular}{c c c} \hline
**Test Number** & **Length of Pile (L)/m** & **Top Burial Depth of Pile (h)/m** \\ \hline
1 (Control group) & 0 & 0 \\ \hline
2 & 8 & 0 \\ \hline
3 & 12 & 0 \\ \hline
4 & 16 & 0 \\ \hline
5 & 16 & 4 \\ \hline
6 & 16 & 8 \\ \hline \end{tabular}
\end{table}
Table 1: Experimental design scheme.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Symbol** & **Dimension** & **Similarity Ratio** \\ \hline Gravitational acceleration & \(g\) & L-T\({}^{-2}\) & 50 \\ Geometric dimension & \(L\) & L & 1/50 \\ Displacement & \(D\) & L & 1/50 \\ Density & \(\rho\) & M-L\({}^{-3}\) & 1 \\ Time & \(T\) & T & 1/50\({}^{2}\) \\ Strain & \(\epsilon\) & - & 1 \\ Stress & \(\sigma\) & M-T\({}^{-2}\).L\({}^{-1}\) & 1 \\ Elastic modulus & \(E\) & M-T\({}^{-2}\).L\({}^{-1}\) & 1 \\ Bending stiffness & \(EI\) & M-T\({}^{-2}\).L\({}^{3}\) & 1/50\({}^{4}\) \\ Bending stiffness per unit length & \(EI\) & M-T\({}^{-2}\).L\({}^{2}\) & 1/50\({}^{3}\) \\ Bending moment & \(M\) & M-T\({}^{-2}\).L\({}^{2}\) & 1/50\({}^{3}\) \\ Bending moment per unit length & \(M\) & M-T\({}^{-2}\).L & 1/50\({}^{2}\) \\ \hline \end{tabular}
\end{table}
Table 2: Centrifuge modelling parameter similarity ratio (model/prototype).