*5.2. Monitoring Data Analysis*

During construction, the monitoring in the jacking process is the most critical stage of the project. The underpinning jacking adopts the graded loading, this process is divided into 10 stages, and the interval is 10% of the predetermined limit of loading. Each loading stage is held for 10 min until the tested displacement parameters are stable and meet the limit requirements (controlled by 0.1 mm/h), and then the next stage of loading can be carried out. After the static compression of the new pile is completed (reaching the design control value of the jacking force), the monitorization continues until the settlement is stable (consecutively controlled by 0.1 mm/h for 12 h). During the pile-cutting stage, the settlement of the pier and underpinning beam are continuously monitored (including the difference in settlement change), and sudden displacement of the underpinning structure is not allowed. At the same time, the pier settlement and underpinning beam settlement (including differential settlement changes) are continuously monitored, and sudden displacement of the underpinning structure is not allowed. In order to focus on the study of the deformation law of the main structure in the lower part of the bridge during the three important stages of jacking, unloading and pile cutting in the underpinning project, the change of the monitoring data of the key nodes of the C15 pile foundation construction was analyzed. As shown in Figure 10, the data of monitoring points are the same as that of the extraction points in the numerical simulation. Measuring points 6 and 7 are the new pile settlement monitoring points, and measuring points 8 and 9 are the underpinning beam settlement monitoring points. The inclinometer is placed on the top of the pier column (measurement point 10).
