## 5 Test Results  
### Deformation and Cracking of Secondary Lining  
Figure 15 shows the deformation development curve of the secondary lining under four test cases, and the values have been converted to the prototype lining result. It can be seen that in different test cases, the sequence of the deformation values of the six monitoring positions is the same. The order from the largest to the smallest are the vault, the arch waist, and the arch foot, and the inverted arch. The deformation amount of the arch foot and the inverted arch is not that different, while the deformation of the lining vault is always the maximum, whose increasing rate is enormous. The sequence of the deformation of the vault from large to small is case 4, case 2, case 3, and case 1. The vaults deformation under the unilateral slide surface immersion cases (cases 2 and 4) is higher than that of the bilateral slide surface immersion cases (cases 1 and 3). The loading step from 10 to 15 is the loading stage of slide surface immersion simulation, where no matter on what side the slide surface is immersed, the deformation of the vault always increased at the maximum speed, and the deformation of the arch foot and inverted arch changed little. In bilateral slide surface immersion cases (cases 1 and 3), the deformation of the arch waist on both sides of the lining had little difference. In contrast, in unilateral slide surface immersion cases (cases 2 and 4), the deformation of the arch waist on both sides of the lining showed a difference, which increased rapidly in the next loading stage (after loading step 15). Generally speaking, the immersion of the slide surface had the most significant effect on the deformation of the lining vault and arch waist. The numbers in Figure 15 are the lining cracks numbers, and the points indicated by the arrows are the deformation monitoring points closer to the crack, whose corresponding load step is the cracking time. The occurrence of the cracks can be considered as the result of the large deformation of the lining. From the perspective of the effect of the cracks on the deformation, after No. 1 cracks in the inverted arch, Nos. 2, 3, and 4 cracks in the arch foot in Figure 15a; Nos. 1 and 4 cracks in the inverted arch, and Nos. 2 and 5 cracks in the arch foot in Figure 15c appears, where the trend of the deformation curve of the arch foot and the inverted arch was unchanged. Therefore, the lining cracking at the arch \begin{table}
\begin{tabular}{c c c} \hline \hline
**Loading Stage** & **Loading Scheme** & **Load Steps** \\ \hline First: non-immersed simulation & Non-immersed load divided into 10 equal parts to load step by step. & 1–10 \\ Second: immersing simulation & Load value in 1–5 m width immersion is divided into five times to load. & 11–15 \\ Third: instability simulation & Load difference between the immersion width of 4 m and 5 m is loaded step by step. & 16 instability \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Loading scheme. foot and the inverted arch is less relevant to the deformation. However, in the lining vault and the arch waist, there is an individual relationship between the lining cracking and the sudden increase of deformation. Some cracks appeared at the inflection point of the curve trend, such as the No. 5 crack in the right arch waist in case 1, the No. 3 crack in the vault in case 3, the No. 2 crack in the left arch waist in case 2, and the No. 2 crack in the right arch waist in case 4. Figure 16 shows the distribution of the secondary lining cracks under the four test cases as well as the cracking sequence with the number in the figure. It can be seen that the lining cracks are symmetrically distributed in the bilateral slide surface immersion cases (cases 1 and 3) except for the inner surface of lining under case 3 (Figure 16a,c). In the cases of unilateral side sliding surface immersion (cases 2 and 4), the cracks are concentrated on the immersion side of the slide surface (Figure 16b,d).