## 4 Results and Discussion
### Analysis of Excavation Sequence
#### 4.1.1 Deformation Analysis
Similarly, when comparing the excavation sequences \"1234\" and \"2134\" as shown in Figure 9,c, it could be seen that the maximum horizontal displacement of the middle partition wall 1 was smaller in the \"1234\" sequence compared to the \"2134\" sequence. Furthermore, from the overall perspective of Figure 9, the tilting amplitude of the middle partition wall 1 was generally greater than that of the middle partition wall 2. This was due to the way the middle partition wall was subjected to forces, as shown in Figure 10. P4 represented the trapezoidal distributed soil pressure acting on the top of the double-arch tunnel. Due to the different surrounding rock pressures, the magnitude of the forces on the supporting structures on both sides was not the same, resulting in P1 > P2. The difference between the two forces caused the middle partition wall to deflect towards the shallow side. In addition, due to the tilting of the top of the middle partition wall, the rock pressure acting on the top of the wall included not only the vertical pressure P5 but also the lateral pressure P3 in the horizontal direction. The size of the top of the middle partition wall was generally much smaller than its burial depth. According to [PERSON]'s principle, the trapezoidal load acting on the top of the middle partition wall could be equivalent to a uniformly distributed rectangular load. Among them, P5 did not cause the tilting of the middle partition wall, while P3 caused the deflection towards the deep side. This  
Figure 8: Deformation of measurement points with construction steps: (**a**) measurement point A; (**b**) measurement point B; (**c**) measurement point C.  
reduced the tilting amplitude of the middle partition wall towards the shallow side. P3 increased with an increase in burial depth; however, the difference between P2 and P1 did not increase. Therefore, the tilting degree of middle partition wall 1 would be greater than that of middle partition wall 2. The change process of the horizontal deformation of the top of the middle partition walls with the excavation steps under different excavation sequences is shown in Figures 11a and 11b, respectively. The deformation curves of the septum wall fluctuated repeatedly for both the deeply buried side and the shallowly buried side. This indicated that the middle partition walls were subject to frequent disturbances during the construction of the tunnel. First, the horizontal deformation of the top of the partition wall on the shallowly buried side was analyzed, as shown in Figure 11a. It could be seen that the horizontal deformation of \"1234\", \"1243\", \"3412\", and \"4312\" was smaller. These were compiled into  
Figure 10: Diagram of the force on the middle partition wall. Figure 9: Horizontal deformation of the central partition wall under different excavation schemes: (**a**) excavation sequence of “1234”; (**b**) excavation sequence of “1243”; (**c**) excavation sequence of “2134”. set A. Next, the horizontal deformation of the top of the partition wall on the deeply buried side was analyzed, as shown in Figure 11b. It could be seen that \"1234\", \"2134\", \"3412\", and \"3421\" were smaller. These were compiled into set B. The intersection of set A and set B was taken, i.e., \"1234\" and \"3412\", which had the most balanced control effect on the horizontal deformation of middle partition walls.