## 4 Monitoring Results and Analysis  
Analysis of Deformation Observation Results in the Implementation Stage of Slight-Disturbance Protection Scheme  
The relation curve of level gauge deformation with the implementation time of the protection scheme at each site is shown in Figure 9. The demolition of the existing downlink splayed wall at Site 1. follows the completion of the uplink culvert extension structure construction. The analysis shows that the level gauge deformation increases with the implementation time during the construction of steel sheet piles on the uplink and downlink. The deformation of the level gauge decreases when the I-beam support is installed, among  
Figure 8: Concrete pouring construction drawing. Figure 7: Diagram of the construction sequence of high-pressure rotary piles in the culvert extension section. which the deformation of the level gauge on the upper side of the culvert is 0.139-0.264 mm, while the deformation of the level gauge in the transition section is smaller (<0.1 mm). When the existing splayed wall is chiseled, the deformation of the level gauge on this side has a greater impact, the deformation of the level gauge on the upper side of the culvert tends to decrease, and the level gauge at the transition section tends to increase. For Sites 1 and 2, the deformation amplitude of the level gauges W1-W4 all appear in the steel sheet pile construction stage. These are 0.085, 0.145, 0.364, 0.371, 0.136, 0.197, 0.424, and 0.481 mm, respectively, illustrating that the implementation of the slight disturbance protection scheme has little influence on the existing line. The variations in the above data are the result of composite action during the construction of steel sheet piles, in which lateral force is generated on the existing subgrade structure. While the phenomenon is more obvious in the high-density coarse granule subgrade filler, it plays a role in constraining the lateral deformation of the existing subgrade when the splayed wall is chiseled [20]. The self-weight of the I-beam support structure acts directly on the culvert structure, which has a greater impact on the vertical deformation of the culvert structure, whereby the anti-deformation capability of the culvert structure can be simultaneously improved in the later stage. The demolition of the existing splayed wall reduces the self-weight as well as the constraint effect on the existing line subgrade. Analysis of Deformation Observation Results in the Construction Stage of the Culvert Extension Structure  
The relation curve of level gauge deformation with the construction time of each stage at Site 1 is shown in Figure 10. The composite foundation treatment time of the uplink side was from June 15 to 18, 2021, and the composite foundation treatment time of the downlink side was from July 20 to 24, 2021. The analysis shows that when the composite foundation is under treatment on the uplink side, the deformation of level gauges W-2 and W-3 on the uplink side increases and then decreases with the construction and interval of everyday foundation treatment. The deformation of W-2 on the top of the culvert shows an overall increasing trend with the composite foundation treatment time, while the deformation of W-3 on the transition section is only obvious during the construction of P1 and P3 piles and then shows a decreasing trend. After the completion of composite foundation construction on the uplink side, the bulge deformation of W-2 and W-3 is 0.597 and 0.317 mm, respectively, while the deformation of level gauges W-1 and W-4 is smaller on the downlink side. When the culvert extension structure is under construction on the uplink side, the deformation of level gauges W-2 and W-3 on the uplink side decreases abruptly at the pouring stage of the bottom plate, side plate, top plate, and  
Figure 9: Relation curve of level gauge deformation with the implementation time of the scheme: (a) Site 1; (b) Site 2.  
splayed wall.