## 2 Monitoring Program and Result Analysis
### Analysis of Monitoring Results of Vertical Deformation of the Pier and Track
Five representative bridge piers were chosen for vertical deformation measurements due to their abundance of measurement locations. QD5-2 and QD13-2 are located in close proximity to the road foundation pit. QD10 is situated near the road foundation pit and features a continuous-beam upper-bridge structure. QD7-2 and QD12-2 are positioned at the location of the pile foundation underpinning. Figure 9a displays the time history diagram of vertical deformation at the measurement points of a typical pier. The vertical deformation of QD5-2, QD10, and QD13-2 exhibits a consistent downward tendency throughout the entire process of piling foundation underpinning. However, the settlement range is minimal, with vertical deformation ranging from 0 mm to 0.5 mm. The vertical displacement of QD7-2 and QD12-2 exhibited a declining pattern throughout the construction of the pile foundation, excavation of the foundation pit, and cutting of the piles. The rate of vertical deformation is gradual during pile foundation construction, whereas it is comparatively rapid during foundation pit excavation and pile cutting. Based on the analysis, it can be inferred that the construction of the pile foundation has minimal impact on the vertical deformation of the pier at the location where the pile foundation is supported. However, the excavation of the abument foundation pit and the cutting of the pile have a slightly more significant effect. The vertical deformation of pier measuring points QD7-2 and QD12-2, located at the position of the pile foundation underpinning, exhibited an upward trend during the jacking operation. Eventually, the deformation stabilized. This can be attributed to the influence of the jacking action exerted by the jacking operation. The stabilization indicates the completion of the jacking operation and the commencement of the static observation period. Upon comparison, it is evident that there is a significant disparity in vertical deformation between the pier located at the pile foundation underpinning location and the pier adjacent to the road foundation pit during the jacking operation. The vertical deformation of the former had experienced the most substantial alteration with the greatest velocity during the jacking operation. Hence, it is crucial to prioritize the vertical deformation of the pier at the location of the pile foundation underpinning while performing the jacking operation. Selection of monitoring data from the downstream track vertical deformation measurement point directly above the bridge abument. A time history diagram illustrating the vertical deformation at typical measurement points is depicted in Figure 9b. There is a minor degree of settlement deformation observed at GCS-2, GC10, and GC13-2 during the pile foundation underpinning stage. Settlement deformation is observed in the vertical displacement of GC7-2 and GC12-2 during the construction of pile foundations, excavation of foundation pits for abutments, and cutting of piles. Additionally, upward uplift deformation occurs in the track structure during jacking operations. This deformation corresponds to the vertical displacement trend of bridge piers due to pile foundation underpinning and is caused by the jacking action. During the pile-cutting process, the vertical deformation measuring point located directly above the bridge pier at the position of the pile foundation underpinning shows settlement deformation. However, there is no notable change in the vertical deformation of the track measuring point located directly above the bridge pier near the road foundation pit. This suggests that the process of cutting the pile has a more significant effect on the vertical displacement of the track directly above the pier at the pile foundation underpinning location compared with the track directly above the pier near the road foundation pit.