## 4 Simulation of the Reinforcement Effect of Isolation Piles
### Influence of Different Factors on the Control Effect of Isolation Piles  
#### 4.2.1 Analysis of the Control Effect on Isolation Piles under Different Pile Lengths  
It can be seen from Figure 10 that under the same pile length condition, the farther the isolation pile is from the east line of Line 5 and the closer it is to the shield tunnel, the smaller the maximum displacement of the Line 5 segment, and the better the support effect. Due to the application of the isolation pile, the overall displacement direction of the Line 5 segment is deflected, and its deflection angle is related to the distance between the isolation pile and the east line of Line 5. This shows that the isolation pile can effectively reduce the sinking of Line 5.  
Figure 9: Schematic diagram of the spatial distribution of the isolation pile position.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Model Name**} & \multirow{2}{*}{
\begin{tabular}{c} **Pile Length** \\ **H/m** \\ \end{tabular} } & \multicolumn{3}{c}{**The Distance between the Isolation Pile and the Outer**} \\ \cline{3-6}  & & & **Diameter of the East Line of Line 5 S/m** \\ \hline \multirow{2}{*}{NS2-1} & \multirow{2}{*}{28} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 5 & 6 & 7 & \\ \hline \multirow{2}{*}{NS2-2} & \multirow{2}{*}{36} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 1 & 2 & 3 & 4 \\ \hline \multirow{2}{*}{NS2-3} & \multirow{2}{*}{44} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 5 & 6 & 7 & \\ \hline \multirow{2}{*}{NS2-4} & \multirow{2}{*}{52} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 5 & 6 & 7 & \\ \hline \multirow{2}{*}{NS2-5} & \multirow{2}{*}{60} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 5 & 6 & 7 & \\ \hline \multirow{2}{*}{NS2-6} & \multirow{2}{*}{68} & 1 & 2 & 3 & 4 \\ \cline{3-6}  & & 5 & 6 & 7 & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Isolation pile simulation scheme.  
2.2 Analysis of the Control Effect of Isolation Piles under Different Horizontal Distances between the Isolation Pile and the Outer Diameter of the East Line of Line 5  
As shown in Figure 11, with the same horizontal distance between the isolation pile and the outer diameter of the east line of Line 5, the maximum displacement of the Line 5 segment decreases as the pile length increases. However, when the pile reaches a certain length, the maximum displacement of the Line 5 segment gradually increases, and the pile length at the inflection point is 52 m. The simulation results show that when the pile length is 52 m, the maximum displacement of the Line 5 segment is the smallest, which is 5.75 mm. Moreover, the displacement direction of Line 5 is deflected counterclockwise, and the longer the pile length is, the more obvious the deflection angle, indicating that the segment displacement of Line 5 can be reasonably controlled according to the length of the isolated pile within the effective pile length of the isolation pile.  
Figure 11: Variation in the maximum displacement of the Line 5 segment, with the pile length at a different horizontal distance between the isolation pile and the outer diameter of the east line of Line 5.  
Figure 10: Change in the maximum displacement of Line 5, with a horizontal distance between the isolation pile and the outer diameter of the east line of Line 5 under different pile lengths.  
Comparing the supporting situation and unsupported conditions in Figures 10 and 11 shows that the displacement of the Line 5 segment is significantly reduced after the application of the isolation pile, indicating that the isolation pile is very effective in the isolation of the shield excavation from the existing Line 5.