# Seismic Resilience Evolution of Shield Tunnel with Structure Degradation
## 5 Evolution of Tunnel Seismic Resilience
### Performance of Tunnel Lining
Residual deformation can be considered as structural plastic deformation caused by tunnel segments, joint plasticity, and internal force redistribution in the tunnel structure. Figure 12 shows the recovery rate of tunnel ellipticity caused by the recovery phase after the shield tunnel ellipticity reaches its peak during the seismic load process. As the peak acceleration of the earthquake increases, the recovery rate here is not only related to the stability value at the end of the recovery period but also closely related to the overall deformation of the structure during the loading process. Specifically, when the peak acceleration changes from 0.1 g to 0.3 g, the structure undergoes greater deformation under larger loads, resulting in a larger proportion of its recovery value during the recovery phase. When the seismic acceleration changes from 0.3 g to 0.5 g, the recovery rate decreases. The reason is that as the peak acceleration of the applied seismic load increases, the structure undergoes a certain degree of plastic irreversible deformation. And when a certain limit of plastic deformation is reached, the proportion of irreparable deformation in the overall deformation of the structure is increasing. It was found from Figure 12 that the difference in recovery rates between different degrees of loss gradually decreased during the change of peak acceleration from 0.1 g to 0.3 g. The recovery rate decreased more significantly at 0.5 g when the preload was completely lost compared to other situations. Therefore, it can be concluded that the preload not only has a significant constraint effect on the overall deformation of the structure but also has a significant optimization effect on increasing the structural resilience and reducing the proportion of plastic deformation in the overall deformation during the recovery stage. Figure 11: Time–history of changes in ellipticity. 2. Deformation on Segment Joints  
The radial displacement of the observation points at the adjacent segment joints on the S4 outer arc surface of the segment joint at the arch bottom is selected to obtain the segment joint opening time curve under the seismic load, as shown in Figure 13. The fluctuation trend of segment opening under various working conditions is basically consistent with the application of seismic loads. But, as the peak acceleration increases, the amplitude of the fluctuation significantly increases. When there is no loss of preload, the maximum opening amount at a peak acceleration of 0.1 g is 1.5 \(\times\) 10\({}^{-4}\) mm, 0.309 mm at 0.3 g, and 2.118 mm at 0.5 g. When the preload is completely lost, the maximum opening amount under the action of 0.1 g peak acceleration is 5.5 \(\times\) 10\({}^{-4}\) mm, 1.128 mm at 0.3 g, 2.963 mm at 0.5 g.  
The recovery rate of the segment joint opening under different degrees of lining performance loss under different peak acceleration seismic loads is shown in Figure 14. It  
Figure 12: Recovery rate of ellipticity with the loss of preload. Figure 13: Segment joint opening time curve under seismic load. can be seen from the figure that the difference in recovery rates between different degrees of loss gradually decreases as the peak acceleration of seismic load changes from 0.1 g to 0.5 g. And the difference in segment joint opening under different degrees of preload loss gradually increases with the peak acceleration increases.