# Centrifuge Modelling of the Impact of Excavation with Partition Piles on Adjacent Existing Tunnel
## 3 Results and Discussion
### Displacement of Tunnel  
The primary emphasis in this centrifuge modelling was on the displacement of the tunnel. As illustrated in Figures 10 and 11, the overall deformation of the tunnel took on an approximately ellipsoidal form in the horizontal direction. The maximum horizontal displacement occurred at the tunnel's right shoulder, while the maximum vertical displacement was observed at the right arch. In the control group, the maximum horizontal and vertical displacements constituted around 0.3% and 0.17% of the excavation depth, respectively. [PERSON] et al. [37] obtained a maximum tunnel heave of approximately 0.024% of the excavation depth through centrifuge modelling, while [PERSON] et al. [10] measured the maximum tunnel settlement of 0.014% of the excavation depth in their experiments. Due to limitations in the size of the model box, the tunnel depth in this experiment was relatively shallow and closer to the excavation. Therefore, the final tunnel displacement was somewhat larger compared to the values obtained in the previous literature. Through the comparison within the pile length group, it could be seen that the short partition piles  
Figure 9: Ground surface settlement behind retaining wall, and A and B respectively refer to the number in parentheses in the figure. (**a**) Comparison group of pile length. (**b**) Comparison group of pile length.  
in test 2 had the best control effect on tunnel displacement, with a reduction of 36.7% in the maximum horizontal displacement and 31.8% in the maximum vertical displacement. However, as the pile length increased, the control effect of the partition piles deteriorated, and it even increased the tunnel's displacement. This was because the increase in the pile length led to an increase in its traction effect, resulting in a weakening of the control effect and even a negative effect.  
Through a comparison analysis of the group of top burial depth of pile, it could be observed that, compared to test 4, the top burial depth of pile in tests 5 and 6 had improved the effect of the partition piles. In test 5, the improvement of the top burial depth of the pile in maximum horizontal displacement and vertical displacement reached 46.6% and 23.3%, respectively. However, when compared to the control group, the improvement effect was still insufficient, and the partition piles continued to increase tunnel displacement. Furthermore, when the top burial depth of the pile was too deep and exceeded its critical value, the improvement effect on the partition piles deteriorated. Through analysis, it could be concluded that there was a certain dividing point along the length of the partition pile concerning its displacement control effect on the adjacent tunnel. Below this dividing point, the portion of the pile exhibited a barrier effect on the tunnel displacement caused by excavation. Conversely, above the dividing point, the pile exhibited a traction effect on the tunnel. Therefore, moderately incorporating the top burial depth of the pile weakened the traction effect, thereby improving the displacement control effect of the partition pile.  
Figure 10: Horizontal displacement of the tunnel, and A and B respectively refer to the number in parentheses in the figure. (**a**) Comparison group of pile length. (**b**) Comparison group of pile length.  
However, when the top burial depth of the pile increased to below the dividing point, the barrier effect of the lower part of the partition pile also decreased, and the improvement effect of it on the partition piles deteriorated.