## 4 Results and Discussion
### Illustration of Controversies Regarding Effects of Isolation Piles on Tunnel Deformation
Firstly, with regard to the variation patterns, it is clear in Figures 13-15 that as the isolation pile moved closer to the excavation, the trends in both the horizontal and vertical control efficiencies of the isolation pile were generally consistent, both exhibiting a downward trend. However, as the isolation pile approached the tunnel, the variation trends for the two efficiencies diverged, particularly when the pile length and pile head depth were small. This behavior can be attributed to the mechanism by which the isolation pile controls tunnel deformation, which has been discussed in the previous section and will not be reiterated here. Secondly, regarding the relative magnitudes of the two deformations, when the isolation pile was 2 m away from the excavation and its head depth was less than the tunnel depth (approximately 15 m), the vertical control efficiency of the isolation pile exceeded \begin{table}
\begin{tabular}{l l l l l} \hline \hline
**Pile Head Depth (m)** & \(\leq\)**20** & **25–30** & **35** & **40** \\ \hline \(\leq\)5 & Decrease & First increase, then decrease & First decrease, then increase & First increase, then decrease \\ \(>\)5 & Increase & Increase & & \\ \hline \end{tabular}
\end{table} 
Table 6: The relationships between the variation trends and pile head depth as well as pile length. \begin{table}
\begin{tabular}{l c c c} \hline \hline  & **Close to Pit** & **Middle Part** & **Close to Tunnel** \\ \hline Transition point in & 0.4 & 0.6 & 0.4 \\ length ratio between & 0.8 & 0.8 & 0.8 \\ isolation piles and & 1 & 1.2 & 1.4 \\ retaining piles & 1.4 & 1.4 & \\ \hline \end{tabular}
\end{table} 
Table 5: Transition points of the horizontal control efficiency of isolation piles at different locations. its horizontal control efficiency (Figure 13). Conversely, when the pile head depth exceeded the tunnel depth, the situation reversed. This phenomenon can be explained by the mechanism proposed in this study. Specifically, when the vertical control efficiency of the isolation pile was greater than the horizontal control efficiency, tunnel deformation was primarily influenced by the maximum deformation in the vertical plane of the isolation pile. In contrast, when the horizontal control efficiency was higher, the deformation was predominantly governed by changes in the surrounding soil displacement field around the tunnel. This conclusion is further corroborated by Figure 15, where it can be seen that when the isolation pile was 9 m from the excavation pit and has a shallow head depth, the vertical control efficiency was lower than the horizontal control efficiency. This is consistent with the earlier conclusions from the mechanism section: as the isolation pile approached the tunnel, its blocking effect on tunnel deformation is primarily reflected in the alteration of the surrounding soil displacement field. Finally, regarding whether the isolation piles have a positive effect, for the case where the isolation pile was located 2 m from the excavation and its head depth is shallow, the isolation pile exerted a positive control on both the horizontal and vertical displacements of the tunnel. As the pile moved closer to the tunnel, a shallow pile still positively controlled vertical deformation of the tunnel, while a deeper pile exerted a positive effect on horizontal deformation. Based on the above analysis, the findings can be applied in practical engineering to prioritize the protection of either vertical or horizontal tunnel deformation and to rationally adjust the location and depth of the isolation piles.