# Seismic Resilience Evolution of Shield Tunnel with Structure Degradation
## 6 Conclusions  
This study proposes performance indicators for shield tunnel lining under seismic loads. The structural response and resilience evolution under different initial performance losses and peak acceleration seismic loads were analyzed using a three-dimensional refined finite element model. The main conclusions obtained are as follows:  
(1) Lining performance indicators were established considering the maximum deformation in history, including ellipticity performance indicators that consider the overall deformation of the lining structure and opening quantity indicators that mainly consider the performance of segment joints.  
(2) The structural recovery ability after seismic load is related to the structural lining performance at the initial moment of load action and the lining loss. The smaller the degree of lining loss, the recovery ability is stronger during the recovery stage.  
(3) The deformation of the tunnel structure cannot be fully restored after seismic load. The residual deformation increases with the increase in the initial lining performance loss at the time of seismic load and also increases with the increase in peak acceleration of seismic load.  
This study mainly focuses on the influence of the degree of different initial performance loss degrees of lining on the seismic resilience of shield tunnels. Different degrees of preload loss are used as characterization methods for different degrees of lining loss. As is well known, resilience is a very broad concept in engineering [38; 39; 40]. This study uses two parameters, structural and mechanical performance as well as structural deformation, during seismic loading to reflect the changes in structural performance level during the loading process and then evaluates the resilience of the structure. However, the influence of groundwater was not considered in this study, so formation liquefaction will also be a part of our future research [41; 42; 43; 44]. Overall, this study can provide valuable insights for the early seismic design and later operation and maintenance of shield tunnels, improve the understanding of engineering professionals about the pre-tension in the operation of shield tunnels, and provide a reference for the evaluation of the seismic resilience of shield tunnels [44; 45; 46].  
Conceptualization, H.C., X.B. and X.C.; methodology, H.C., J.S. and R.T.; validation, X.B., Z.H. and T.Q.; formal analysis, X.W. and R.T.; investigation, R.T., T.Q. and Z.H.; data curation, R.T. and X.W.; writing--original draft preparation, R.T. and X.W.; writing--review and editing, J.S. and X.B.; supervision, H.C.; project administration, X.C. and Z.H.; funding acquisition, H.C. and X.C. All authors have read and agreed to the published version of the manuscript.  
This research is fully supported by the National Natural Science Foundation of China (No. 52022060 & 52090084); the National Natural Science Foundation of China (No. 51925804 & 52090084) and the Shenzhen Science and Technology Program (Grant No. KQTD20200909113951005).  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
Author [PERSON] is employed by the China Railway 22 nd Bureau Group Shenzhen Construction Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.