5.2.1. Jacking Stage of Underpinning Pile

As shown in Figure 11, during the jacking process of C15, both the pier and the underpinning beam experience upward displacement within the control range under the action of jacking force. When the jacking is completed, the change of displacement gradually becomes stable without significant fluctuation. The maximum change rate of the pier displacement is −0.25 mm/h, and the cumulative change is 0.23 mm. The maximum change rate of the underpinning beam displacement is 1.28 mm/h, and the cumulative change is 1.32 mm. The maximum change rate of the pier inclination is 0.006◦/h, the cumulative change value is 0.016◦. During the jacking process, the displacement and inclination of the piers are all within the normal range. Among them, the measured value of seven measuring points (new piles near the F ramp) exceeds the control value after the completion of the 7th level of loading, but after the completion of the 10th level of loading, the differential settlement of the new piles is 1.74 mm, and other monitoring items have no abnormality. According to the monitoring results after reaching the jacking design load for 30 h, it is shown that the monitoring data are gradually stable, the final differential settlement of the new pile is 1.66 mm, and the overall monitoring cumulative value and change rate are both small. In the jacking stage, although the settlement of the new pile exceeds the control value, the deformation of the superstructure is stable, which is also the same as the conclusion of the numerical simulation, indicating that the design of the jacking force is reasonable, and the construction plan is feasible.

**Figure 10.** Layout of the monitoring points during underpinning construction (**left**) and the field monitoring (**right**).
