## 4 Field Measurement and Verification of Large Diameter Adjacent Shield Tunnelling Bridge Piles
### Analysis of In-Site Monitoring Results  
Figure 12 shows the vertical displacement of #2 and #3 bridge piles during the shield crossing of No. 1 bridge of Hongling Interchange. The monitoring value 30 m before shield crossing was taken as the initial value to analyze the impact on bridge piles during shield crossing. Before the shield passed through the bridge pile, the maximum vertical displacement of the bridge pile was \(-\)0.84 mm. Before the shield cutter head was driven from the bridge pile to the corresponding segment out of the shield tail, the slurry pressure and synchronous grouting pressure slightly higher than the theoretical value caused the bridge pile to float temporarily. After the shield tail passed through, the bridge pile saw about 1 mm. Through the secondary supplementary grouting measures, the bridge pile floated again. After the grouting was stopped, the monitoring value of the bridge pile had a cumulative settlement of 5 mm until the cutter head was 80 m away from the monitoring point. The maximum vertical displacement during excavation was \(-\)1.48 mm, which is less than the value of numerical simulation analysis to achieve a good reinforcement effect.  
Figure 13 shows the surface settlements of different chainages at the position of the excavation surface during the period from 30 m in front of the No. 1 bridge of Hongling Interchange to 80 m after the shield crossing. Pile #3 of No. 1 bridge of Hongling Interchange is located at ZK0 + 890, and the corresponding chainage of pile #2 is ZK0 + 875. Within 30 m before the cutter head crossed, the surface settlement value of the upper part of the tunnel fluctuated slightly. With the continuous advancement of the shield machine, the ground surface was slightly uplifted. At this time, the pressure at the top of the slurry sum was 1.14-1.16 bar. When the shield cutter head was driven below the monitoring point, the ground surface sank slightly; the settlement value was 0.5 mm, and the corresponding pressure at the top of the slurry silo was 1.18 bar. When the segment below the monitoring point was out of the shield tail, a large settlement occurred at the surface monitoring points near the two bridge piles, and the average synchronous grouting amount in this process  
Figure 11: Layout of monitoring points.  
was 100%. With the continuous tunnelling of the shield, the surface settlement gradually stabilised; the maximum settlement was ZK0 + 895, and the settlement was 35 mm. The ZK0 + 890-900 surface had a significant degree of settlement compared with the surface within the scope of bridge pile reinforcement, indicating that bridge pile reinforcement reduced the disturbance impact of shield construction on the soil. Compared with the numerical simulation value, the on-site monitoring value was smaller, mainly because the grouting measures could be controlled according to the real-time settlement during the construction process to control the pile deformation effectively.  
Figure 14 shows the vertical displacement change of the tunnel vault after the shield passes. After the last section, the supporting trolley started to monitor the displacement of the arch crown after crossing through and stopped monitoring after the shield was  
Figure 12: Vertical displacement of bridge piles.  
Figure 13: Surface settlements of different chainages.  
advanced by 350 m. The maximum displacement of the arch crown was \(-\)2.6 mm and finally stabilized at about \(-\)1.3 mm.