## 4 Analysis of On-Site Monitoring Results of Shield Tunneling under High-Speed Railway Bridges
### Analysis of Monitoring Results
#### 4.2.2 Analysis of Stress Monitoring Results for Pipe Segments  
This article conducts stress monitoring on rings 532 and 534, located under segment numbers, respectively. The two ring pipe segments are located directly below the elevated bridge, and reinforcement meters are arranged for the circumferential and longitudinal steel bars on the outer and inner sides, respectively, to measure stress. Its position is close to the inner and outer curved surfaces of the pipe segment, located in the middle of the steel cage on the inner and outer curved surfaces of the pipe segment. The stress situation between the two ring segments is basically the same. Below, we choose to analyze the data from ring 534, where the positive and negative stress values represent the direction, and the positive value represents the stress pointing from the soil towards the pipe segment.  
As shown in Figures 15 and 16, the initial stress of the circumferential steel bars inside this ring fluctuates within the range of 4 MPa. Subsequently, the overall trend showed a relatively uniform downward fluctuation, and the later stage remained stable within the  
Figure 14: Final surface settlement of the shield tunneling along the right line.  
Figure 13: Final surface settlement of the shield tunnel crossing along the left line.  
range of \(-2\) MPa. During the final monitoring period, there were small-scale fluctuations in the growth rate. The overall fluctuation range of stress remains within (-6, 8) MPa, and the stress of steel bars basically meets the allowable value. The stress of the outer circumferential steel bar is similar to that of the inner circumferential steel bar and fluctuates at higher stress positions in the initial stage. The highest value is close to 9 MPa, slightly higher than the peak stress on the inner side. Subsequently, there was also a relatively uniform downward trend of fluctuations, with stable fluctuations maintained at \(-2\) MPa in the later stage. Similarly, during the final monitoring period, there was a small range of amplitude fluctuations, and the overall stress remained within the range of (-4, 9). The stress of the steel bars basically met the allowable value.  
As shown in Figures 17 and 18, there is a significant stress peak in the longitudinal reinforcement on the inner side of this ring at the initial entry position. The highest value reached 16 MPa, but only appeared once. Subsequently, the overall trend showed a relatively stable downward fluctuation, and the stress in the later stage remained stable within the range of 0 MPa, fluctuating and changing. The overall fluctuation range of longitudinal steel bar stress is within the range of (\(-5\), 15) MPa. The stress of steel bars basically meets the allowable value. The stress variation trend of the outer longitudinal steel bars is relatively close to that of the inner side. However, the time of peak stress occurrence has shifted backwards, and the overall fluctuation amplitude is greater, with the stress significantly higher than the inner side. The overall fluctuation range is within the range of (\(-3\), 17) MPa, and the stress of the steel bars basically meets the allowable value.  
Figure 16: Stress on the outer side of ring 534.  
Figure 15: Stress on the inner side of ring 534.