## 5 Evolution of the Canal's Long-Term Behavior Based on SSD
### Evolution of the Canal's Long-Term Settlements  
In the calculation process, the design water level of the canal, the highest groundwater level of the slope and underground drainage measures are not applicable. The anti-seepage system is damaged, the seepage of the slope is stable, and the interior slope has no boundary flow. Based on the finite element model of the specific cross-section of the deep excavated canal, the characteristic points a, b, c, and d respectively were selected for settlement analysis at the canal bottom, embankment, slope, and top. The water level adopted the canal's design water level, the vehicle load on the first-level bridleway adopted the car-10 level load, the crowd load was 0.3 t/m\({}^{2}\), and the highest groundwater level was 180.218 m.  
The SSD coupling method was used to compute the canal settlements after five years of operation based on the above working conditions. The nephogram of the canal's vertical displacements after a 5-year operation is shown in Figure 12, and the settlement of each distinctive point is shown in Figure 13. The highest vertical displacement of the canal was 4.151 mm, which was within the authorized settlement range, as shown in the figures. The U2 is the vertical component of the total settlement U. Based on the foregoing conclusions, a numerical simulation of the deep excavated canal is carried out, and a nephogram of the canal's settling clouds after ten years of operation is obtained (see Figure 14). According to the nephogram of canal settlements, the settlement curve of each characteristic point was obtained (as shown in Figure 15). It can be seen from the figures that the maximum settlement is 5.128 mm, which represents an increase of 0.977 mm compared to the five years of operation. This change is not significant, so it is believed that the settlement has reached the final settlement. Table 1 shows the settlement rate of the canal top's characteristic point at different times after the 10-year operation. The canal subsides at a decreasing rate after its operation. After 10 years of  
Figure 11: Canal pore pressure contour when t = 20 years. Figure 12: Canal settlement nephogram when t = 5 years. Figure 13: Settlements of each characteristic point when t = 5 years. operation, the canal settlement rate is 0.16 mm/year. Although its absolute number is minimal and may not have much impact, the settlement continues. The numerical simulation is repeated to investigate the deep excavated canal's long-term settlement and deformation to get the nephogram of canal settlements after 20 years of operation, as shown in Figure 16. It is evident from the figure that the maximum settlement is very close to that calculated after 10 years of operation, indicating the deep excavated canal has reached a stable state, as shown in Figure 17. However, in actual operation, the stability of the deep excavated canal is affected by many factors such as complex water distribution conditions and varying environments, and significant settlements can occur locally. As the operating time increases, the canal's settlement becomes smaller, not affecting its operating safety. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Time/Year** & **1** & **2** & **3** & **4** & **5** \\ \hline Rate (mm/year) & 1.38 & 0.98 & 0.64 & 0.5 & 0.4 \\ Time/year & 6 & 7 & 8 & 9 & 10 \\ Rate (mm/year) & 0.24 & 0.18 & 0.17 & 0.165 & 0.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Canal top’s settlement rate. Figure 16: Canal settlement nephogram when t = 20 years. Figure 14: Canal settlement nephogram when t = 10 years. Figure 15: Settlement of each characteristic point when t = 10 years. In this paper, the hypothetical SSD coupling method was used to predict the life and performance of the deep excavated canal in the SNWDP Xichuan Section. The numerical results showed that under normal operating conditions, the canal may only subside a little after 20 years of operation. The numerical simulation in this paper is based on the coupling of the seepage field and the stress field.