## 5 Results and Analysis
### The Impact on the Total Displacement of the Selected Cross-Section of the Tunnel  
The excavation of the foundation pit induces combined horizontal and vertical displacements at various points on the tunnel cross-section. The change in the total displacements of the selected cross-section (absolute values) for each node under the three excavation sequencing plans is illustrated in Figure 13.  
Overall, the trends in the total displacement of the selected cross-section changes align with those of vertical displacement, indicating that total displacement changes are predominantly driven by vertical displacements, with a relatively minor influence from horizontal displacements. This observation emphasizes the crucial impact of vertical displacement (uplift). At the beginning of the construction period, total displacements exhibit a decreasing trend, attributed to the higher density of the diaphragm wall compared to the original soil. The construction of the diaphragm wall induces a significant displacement in the surrounding strata, resulting in an initially large value for total displacement, primarily manifested as vertical settlement. As each excavation plan progresses, the excavation of soil on one side of the pit causes an overall uplift of the tunnel. The total displacements under all plans gradually increase. Similar to the vertical displacement pattern, sequential excavation (Plan 1) demonstrates lower vertical displacement in the first half of the construction period. In the latter half, increased soil volume leads to an increase in vertical displacement, but the overall displacement remains relatively low. Simultaneous excavation (Plan 2) maintains a relatively higher total displacement throughout the excavation period. Comprehensive excavation (Plan 3), combining features of the first two plans, initially resembles simultaneous excavation and then switches to sequential excavation. Figure 13: Comparison chart of total displacement variation at various nodes for different excavation sequence scenarios. (**a**) Node: 61174, (**b**) Node: 5792, (**c**) Node: 59140, (**d**) Node: 7569. By transforming the global coordinate system to the position of the tunnel cross-section, a two-dimensional polar coordinate graph depicting the movement trend of the tunnel cross-section is presented in Figure 14. This figure illustrates the movement trend of the tunnel cross-section under the comprehensive excavation plan, with the movement distances magnified by a factor of 5E3 for better visualization. The figure shows the initial state of the tunnel (Condition 0) located at the coordinate axis's endpoint. After the construction of the diaphragm wall in preparation for excavation (Condition 4), the tunnel exhibits an overall trend toward the excavation pit and a slight sinking tendency. The tunnel structure's out-of-roundness is relatively small during this process because the overall vertical and horizontal displacements are approximately equal, as indicated by Figures 11 and 12. After excavation, the tunnel position continuously uplifts towards the excavation pit until the soil excavation is complete. Figure 15 demonstrates that the initial movement trend of the tunnel is dominated by vertical and horizontal displacement in the early stages. As soil excavation commences, the increase in vertical uplift becomes more pronounced than the horizontal movement. In the polar coordinate graph, this is reflected by a more noticeable vertical uplift, highlighting the dominant role of vertical displacement in the later stages of excavation. The differing magnitudes of vertical and horizontal increases during soil excavation contribute to an increasing out-of-roundness in the tunnel structure. During the initial and first soil excavation step (Condition 4), the overall out-of-roundness of the tunnel structure is relatively small.