## 4 Results and Discussion
### Analysis of Excavation Sequence
#### 4.1.2 Force Analysis
Figure 12: Stress cloud diagram of support structures under different excavation sequences: (**a**) excavation sequence of “1234”; (**b**) excavation sequence of “1243”; (**c**) excavation sequence of “2134”; (**d**) excavation sequence of “2143”; (**e**) excavation sequence of “3412”; (**f**) excavation sequence of “3421”; (**g**) excavation sequence of “4312”; (**h**) excavation sequence of “4321”. Figure 13: The maximum stress of the left and right lines of the support structure: (**a**) the shallowly buried side; (**b**) the deeply buried tunnel side. (2) Stress analysis of the middle partition wall  
The distribution pattern of the main stresses in the middle partition wall under different excavation sequences was similar. Taking the excavation sequence of \"1234\" as an example, its maximum and minimum principal stresses are shown in Figures 13(a) and 13(b), respectively. It can be seen from Figure 13 that the stress in the middle partition wall on the deep side was greater than that on the shallow side, regardless of the excavation sequence. From the distribution areas of the maximum principal stress and minimum principal stress, the middle partition wall produced a concentrated tensile stress area at its bottom. The compressive stress area of the middle partition wall was mainly concentrated on both sides. Considering the weak tensile properties of concrete, the anchorage at the bottom of the diaphragm wall should have been strengthened in design and construction to prevent its damage due to excessive tensile stresses. Under different excavation sequences, the maximum tensile principal stress of the middle partition wall on the shallowly buried side and deeply buried side is shown in Figures 14(a) and 14(c), respectively. The maximum compressive principal stress on the shallowly buried side and deeply buried side is shown in Figures 14(b) and 14(d), respectively. Considering the weak tensile properties of concrete, it was important to prioritize the reduction of the tensile stresses experienced by the middle partition wall. Figure 14(c) illustrates the maximum tensile stresses in the middle partition wall on the deeply buried  
Figure 13: Principal stress of the central partition wall: (**a**) the tensile principal stress; (**b**) the compressive principal stress. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Excavation Sequence**} & \multirow{2}{*}{**Tunnel 1**} & \multirow{2}{*}{**Tunnel 2**} & \multicolumn{2}{c}{**The Larger between**} & \multicolumn{2}{c}{**The Larger**} \\  & & & **Tunnel 1 and** & **Tunnel 3** & **Tunnel 4** & **between Tunnel 3** \\  & & **(MPa)** & **(MPa)** & **(MPa)** & **(MPa)** & **and Tunnel 4** \\  & & & **(MPa)** & & **(MPa)** \\ \hline
1234 & 5.227 & 5.106 & 5.23 & 10.140 & 5.544 & 10.14 \\
1243 & 5.262 & 5.145 & 5.26 & 5.330 & 10.750 & 10.75  
side under different excavation sequences. Among the four excavation sequences of \"1234\", \"2134\", \"3412\", and \"3421\", better results were achieved, and they were organized into set E. Regarding the maximum tensile stress of the middle partition wall on the shallowly buried side, as shown in Figure 15a, the four excavation sequences of \"1234\", \"1243\", \"3412\", and \"4312\" achieved better results and were organized into set F. By taking the intersection of set E and set F, it was determined that the two excavation sequences \"1234\" and \"3412\" were the best in terms of reducing the tensile stresses on the middle partition wall. This finding aligned with the excavation order obtained after analyzing the force state of the support structure.