## 5 Analysis of the Numerical Results
### Transverse Settlement of the Ground Surface  
#### 5.2.1 When C/H = 0.764  
According to the findings of similar surface settlement studies, the maximum settlements resulting from a single-cavern excavation are almost all located at the tunnel axis position. Thus, to better reflect the relevant influence characteristics of intersecting tunnels on the surface deformation, this section continued to analyze the lateral settlement law of the ground surface. As shown in Figure 7, a settlement research line was arranged at 30 m intervals from the excavation direction. The three lines separately corresponded to three special spatial locations: the sites of critical separation, and the short-distance and long-distance separations of the new tunnel from the existing tunnel. First, it is clear from Figure 11 that the increase in the surface load also caused greater settlement, and that the settlement trough shapes of the curves are distinct. According to Figure 11a, the backfilling of the existing tunnel was markedly influential on the surface settlement at this time. The maximum settlement was about 11.6 mm in the absence of backfilling, while it was only 8.3 mm in the presence of backfilling, showing a decrease of approximately 28.4%. At line 2, the difference in settlement attributed to the existing tunnel backfilling was reduced to about 20%, while at line 3, such a difference was already inconspicuous. This fully explained why the distance from the existing tunnel to the new tunnel was also a sensitive factor affecting the surface settlement. Additionally, as the centerline of new tunnel coincided with the centerline of the overlying road at D/W = 0.378, the symmetry axis of the settlement trough curve coincided with the tunnel and road centerlines in the \"hty\" condition. Furthermore, in the \"htt\" condition, the symmetry axis of the settlement trough curve shifted toward the existing tunnel direction. This kind of phenomena has also been studied by many scholars. With the continuous separation of the new tunnel from the existing tunnel, the corresponding surface settlement continued to decrease as well. Eventually, the maximum settlement at line 3 was approximately 7.6 mm, and the symmetry axes of all settlement curves coincided. Figure 11: Longitudinal surface settlement of model A-A with D/W = 0.378. Figure 12 also reflects a relevant law. The maximum settlements at lines 2 and 3 changed insignificantly compared to Figure 13, although the maximum settlement corresponding to the \"htm\" condition shown in Figure 14a was close to 14 mm. This again explained why the intersection (line 1) between the new and existing tunnels was a sensitive zone that affected the change of the surface settlement at a constant C/H ratio of 0.764. Furthermore, a comparison of Figures 11a and 12a shows that the D/W reduction affected the settlement in the \"htm\" condition only. The root cause was an inconsistency of the effective tunnel span at line 1 in the \"htm\" condition. Thus, \"htm\" was a sensitive factor influencing settlement at this time. When D/W = 0.251, lines 1 and 2 were deviated from the tunnel axis such that the symmetry axis of the settlement curve was biased to the left of the road centerline in the \"hty\" condition. In contrast, in the \"htm\" condition, the symmetry axis of the settlement curve was biased to the right of the road centerline. Moreover, in view of the far smaller sectional size of the existing tunnel than the new tunnel, the eccentricity of the settlement curve symmetry axis in the \"htm\" condition was significantly lower than that in the \"hty\" condition. On the other hand, the symmetry axes of all the settlement curves for line 3 shown in Figure 12c coincided with the tunnel center, which were still located on the left side of road centerline as well. The settlement value was affected only by the surface load magnitude. The settlement law presented in Figure 13 differs from that in Figures 11 and 12, and the cause of such a difference has been explained earlier.