## 4 Analysis, Results, and Discussion
### Displacement Analysis
#### 4.1.2 Tunnel-Surrounding Rock Deformation  
The surrounding rock displacement can directly reflect the main parts and changing trends of tunnel failure deformation. Thus, it is an important index for determining the stability of the surrounding rock and supporting structure. The displacement contour and the vertical displacement curve of each monitoring point after tunnel excavation are shown in Figures 8 and 9, respectively. Figure 8: Contours of the tunnel displacement: (**a**) excavation of the left tunnel; and (**b**) excavation of the right tunnel. As shown in Figures 8 and 9, at the end of the left tunnel excavation, the tunnel exhibited asymmetry in the surrounding rock deformation. The maximum subsidence value was 14.314 mm on the right arch shoulder due to the right thickness and left thinness of the overlying terrain. The tunnel was affected by eccentric pressure. Therefore, in the construction process, the surrounding rock stress and lining deformation of the right arch shoulder should be monitored emphatically; the surrounding rock of the arch bottom uplifted, and the maximum uplift value was 12.539 mm at the center of the inverted arch. Due to the timely initial support of the excavation position, the deformation of the tunnel top in the early stage was small, and the maximum settlement value was limited to 5.238 mm. With the gradual excavation, the cumulative deformation value gradually increased. However, the deformation trend was reduced until the excavation face was advanced to 25 m, and the deformation of the top surrounding rock tended to be stable. At the early stage of excavation, the arch bottom was not excavated and the inverted arch  
Figure 9: Vertical displacement curve of the inner contour monitoring point: (a) the left tunnel; and (b) the right tunnel. could not be applied. Thus, the deformation increment of the arch bottom was larger than that of the arch top, and the maximum bulge value was 6.415 mm until the deformation of the arch bottom stabilized after the excavation surface advanced to 30 m.  
At the end of the right tunnel excavation, the surrounding rock deformation was symmetrically distributed, indicating that it was not affected by the eccentric pressure, and the excavation of the right tunnel had little effect on the deformation of the surrounding rock of the left tunnel. As the overlying rock layer of the right tunnel was thick, the settlement and uplift values were greater than those of the left tunnel. The maximum settlement value was found as 17.952 mm, and the maximum uplift value was 16.748 mm, appearing in the arch crown and the center of the inverted arch, respectively. As shown in Figure 9b, the short-term displacement of the surrounding rock changed significantly after each step of rock and soil excavation. Most of the surrounding rock deformation reached stability when the excavation reached 20 m. After the tunnel excavation was completed, vertical displacement contours were intercepted vertically at the center of each tunnel along the tunnel axis direction. Five monitoring points were arranged along the axial direction at the arch bottom of each tunnel, and the change curve of vertical displacement of each monitoring point was obtained, as shown in Figures 10 and 11. As shown in Figures 10 and 11, from the stratigraphic distribution, due to the tunnel passing through a rock stratum with a different weakening degree, although the deformation at the top of the surrounding rock is the same, the uplift area at the bottom of the surrounding rock is not unevenly distributed along the axis, and the uplift value gradually decreases. From the changes of the curves, it can be seen that the uplift value of the arch bottom had a similar trend and tended to stabilize after the excavation surface advanced 20-25 m. The uplift value of the tunnel front-end was larger than the tunnel back-end. Due to the greater burial depth of the right tunnel, the uplift value of the right tunnel was larger than that of the left tunnel.