## 6 Conclusions  
In this study, the SSD coupling method was adopted. The canal \"lining-foundation\" is considered a whole coupled system. The concrete lining's damage and the foundation's seepage damage were linked together, and long-term effects were introduced for numerical simulation and analysis of the canal lining structure. The conclusion is summarized as follows:  
1. The applicability of the SSD coupling method to the SNWDP in China: The long-term settlement of the canal and the modification of the seepage field were investigated by using a constitutive coupled plastic damage model of nonlinear dynamic damage of concrete, which is used in the numerical simulation of the coupled seepage-stress model. After five years of operation through modeling, the maximum settlement of the deep excavated canal in the SNWDP Xichuan Section is 4151 mm, which is consistent with the monitoring data, thus verifying the rationality of the numerical simulation method.
2. Prediction on the settlement of the canal after long-term operation: Through the numerical simulation of the settlement after 10 years of operation, it is found that the maximum settlement is 5.128 mm, and the canal settlement mainly occurred in the first two years. Numerical simulations were used to obtain the settlement  
Figure 20: Damage-distribution cloud diagram after 50 years.  
nephograms after 20 and 50 years of operation. It is evident from the nephograms that the settlement finally remains the same.
3. The damage evolution process of the canal after long-term operation: Judging by the overall damage of the lining plates on the canal of the SNWDP, the lining plate on the left bank was damaged first, and the damage was concentrated near the water level. After a long-term operation, the lining structure of the deep excavated canal in the SNWDP Xichuan Section is still safe, and there is no apparent damage.
4. Causes of the damage and limitations of this study: The deep excavated canal in the SNWDP Xichuan Section is destroyed from the water surface, mainly due to the seepage of the high underground water. The damage spreads gradually from the local area, eventually leading to failure of the concrete lining plate. However, this study was limited by the environment, climate, and rainfall intensity. Therefore, more other influencing factors need to be studied further.  
Conceptualization, X.X. and W.X.; methodology, C.X.; software, C.X.; validation, W.X. and C.X.; formal analysis, W.X.; investigation, W.X.; resources, X.X.; data curation, X.X.; writing--original draft preparation, W.X.; writing--review and editing, W.X. and M.Y.A.K.; visualization, W.X.; supervision, X.X.; project administration, X.X.; funding acquisition, X.X. All authors have read and agreed to the published version of the manuscript.  
This study was supported by the National Key Research and Development Program of China (Grant No. 2018 YFC0406901), the National Natural Science Foundation of China (Grant No. 51979109), Henan Science and Technology Innovation Talent Program (Grant No. 174200510020), and Henan Province University Science and Technology Innovation Team Support Plan (Grant No. 19 IRTSTHN030). These supports are gratefully acknowledged and greatly appreciated.  
Not applicable.  
The authors declare no conflict of interest.