## 3 Results and Discussion
### Typical Profile Analysis
#### 3.2.3 Characterization of Bottom Plate Measurement Points  
Based on the data of total displacement, the von Mises stress, and the high and low tilt values of the centerline of the bottom plate of the step tunnel at the time of tunnel penetration under different excavation methods, the control effect on the mechanical response of the bottom plate of the existing tunnel is analyzed. Figure 22 shows the total displacement and settlement curves of the existing tunnel base plate under different excavation methods, which shows that the total displacement and settlement of the existing tunnel's base plate under different excavation methods are consistent. Taking the centerline of the left and right tunnels as the axis, the data of the left and right measurement points are symmetrically distributed and the value of the right measurement point is slightly larger than the value of the left measurement point, which is mainly due to the fact that the left tunnel is the first one to be excavated, which is caused by the spatial mechanical effect. The settlement value of the area between the intersection points of the left and right tunnels is the largest, the settlement value gradually decreases to both sides, and, after a certain distance, it is an overall uniform settlement area. In the area between the intersection points, the displacement settlement order is as follows: upper and lower step blasting method excavation settlement value of up to 3.09 mm, upper and lower step static method excavation settlement value of up to 2.64 mm, CD blasting method excavation settlement value of up to 2.35 mm, and CD static method excavation settlement value of up to 1.97 mm; outside the intersection point of the left side of the region, using the upper and lower step blasting method, the upper and lower step static method, and the CD method, the excavation settlement value is similar and greater than that of the CD static method; outside the intersection point of the right area, using the upper and lower step blasting method, the CD blasting method, and the CD static method, the excavation settlement value is similar and less than that of the upper and lower step blasting method. For the location of the settlement sensitive area between measurement points 6 and 16, the distance is 130 m.  
Figure 23 shows the change curve of von Mises stress in the centerline of the existing tunnel base plate after different excavation methods are adopted for the new tunnel, and the change rule is consistent. Taking the left and right tunnel centerline as the axis, the data of left and right measurement points are symmetrically distributed and the values of von Mises stress change in the middle line of the base plate of existing tunnels using the four excavation methods are similar. The left and right intersection area von Mises stress negative change is the largest; for the high decompression area, the upper and lower step blasting method excavation maximum negative value changes to \(-669\) kN, the upper and lower step static method excavation maximum negative value changes to \(-591\) kN, the CD blasting method excavation maximum negative value changes to \(-593\) kN, and the CD static method excavation maximum negative value changes to \(-683\) kN; the center of the lower tunnel link is the medium decompression area and the negative change of the stress  
Figure 22: Total displacement and settlement curve of the base plate of existing tunnels with different methods of excavation.