## 5 Test Results
### Internal Force of Secondary Lining
#### 5.2.2 Sidewall Sections 7-10 in Cases 2 and 4  
Figure 18 shows the internal force curve of Sections 7-10 of the sidewall in the unilateral slide surface immersion cases (cases 2 and 4). The sections 7-10 are the monitor sections in tunnel sidewall, as shown in Figure 13a. Figure 18a,b illustrates the axial force and bending moment curve of the four sections of sidewall under the unilateral arch foot slide surface immersion case (case 2), respectively. It can be seen in Figure 18a that the lining sidewall was compressed during the test. The axial force of Sections 8 and 10 on the side of the immersion slide surface was more significant than that of Sections 7 and 9 on the other side. The axial force of Sections 9 and 10 near the arch foot was greater than that of the Sections 7 and 8 on the upper side. The bending moment variation curve also showed the same law. At the loading step 16, the crack 2 passed through the strain gauge at Section 8. The strain gauge failed, and the strain data overflowed. The external surface of the sidewall cracked, and the axial force of Section 8 increased suddenly. The axial force trends at other locations did not change. It can be seen from Figure 18b that Sections 9 and 10 always bent inward, and Sections 7 and 8 always bent outward, before the lining lost stability. At the loading step 16, the bending moment of Section 7 began to decrease and finally changed from bending outward to bending inward.  
Figure 17: Internal force curves of the arch Sections 1–6: (**a**) axial force in case 1, (**b**) bending moment in case 1, (**c**) axial force in case 3, and (**d**) bending moment in case 3.  
Figure 18c,d show the axial force and bending moment curve of the four sections of sidewall under the unilateral arch waist slide surface immersion case (case 4) respectively. It can be seen from Figure 18c that the lining sidewall was compressed during the test. The axial force of Sections 8 and 10 on the side of the immersion slide surface was greater than that of Sections 7 and 9 on the other side, respectively. The axial force of Sections 9 and 10 near the arch foot was smaller than that of the Sections 7 and 8 on the upper side. The bending moment variation curve showed the same law. During the second loading stage (loading step 10-15), the axial force of Sections 7 and 8 in the upper side increased slowly, while that of Sections 9 and 10 in the lower side did not change much. When the immersion width reached 4 m (loading step 14), the No. 2 crack appeared on the sidewall of the immersion sliding surface side, but the changing trend of the axial force of the sidewall did not changed. Compared with Figure 18a,b, the axial force of sidewall under case 4 was generally smaller than that of sidewall under case 2. It can be seen from Figure 18d that Sections 7 and 8 at the upper side of the sidewall always bent to the outside, and Sections 9 and 10 at the lower side of the sidewall always bent to the inside. After the No. 2 crack of the sidewall in the immersion slide surface side appeared, the bending moment of Sections 7 and 8 stopped increasing and became stable, while the bending moment of Sections 9 and 10 continued to increase.  
Comparing the values of internal force under the four cases, the lining bending moment under the unilateral slide surface immersion cases was significantly higher than that under the bilateral slide surface immersion cases, while the axial force of most sections unilateral slide surface immersion cases was less than that under the bilateral slide surface immersion cases. The immersion of bilateral or  
Figure 18: Internal force curves of the sidewall Sections 7–10: (**a**) axial force in case 2, (**b**) bending moment in case 2, (**c**) axial force in case 4, and (**d**) bending moment in case 4.  
unilateral slide surface determined the magnitude of the bending moment of the lining. The influence of lining cracking on the lining bending moment was more significant than that on the axial force.