## 3 Test Results and Analyses
### Influence of the Interface Form on the Load-Bearing Performance of Rehabilitated Pipes
#### 3.3.1 Damage Form  
The damage form of specimen S-1 (naturally bonded interface) is shown in Figure 8, and the crack width is shown in Figure 9. At the initial stage of loading, there was no damage to the specimen. When the displacement reached 2.30 mm, penetrating cracks occurred at the top and bottom of the pipes. The crack at the top of the tube is shown in Figure 9a, and the crack width was 0.29 mm. Subsequently, cracks appeared above the arching line on both sides of the pipe sections and the load was 11.40 kN. When the displacement reached 2.95 mm, the load increased to an ultimate load of 11.70 kN. With the increasing load, a crack developed along the interface. The interface peeled off when the displacement reached 3.24 mm, as shown in Figure 9b. At this time, the crack width was 0.60 mm and the load value was 11.31 kN. During the later stage of loading, the specimen no longer produced new cracks; the cracks at the top of the pipes expanded rapidly and the specimen failed. The cracks at the top and bottom of the tube are shown in Figure 9c,d, and the crack widths were 4.96 and 1.25 mm, respectively. Figure 8: Damage form of a pipe section with a naturally bonded interface: (**a**) Cracking; (**b**) stripping of the interface; (**c**) sabotage. Figure 9: Schematic diagram of the crack width of pipe sections with a naturally bonded interface: (**a**) Top pipe cracking; (**b**) stripping of the interface; (**c**) top pipe crack at the time of damage; (**d**) bottom pipe crack at the time of damage. The damage form of specimen S-2 (interfacial pegging) is shown in Figure 10, and the crack width is shown in Figure 11. From Figure 10, it can be seen that when the displacement reached 2.60 mm, penetrating cracks occurred at the top and bottom of the pipes. As shown in Figure 11a,b, the crack widths were 0.35 and 0.21 mm, respectively. Moreover, two center-symmetric cracks appeared near the arch line of the pipe sections, and the load at this time was 20.83 kN. When the displacement reached 2.95 mm, the load increased to 21.96 kN. With further increases in the load, the cracks continued to expand. However, unlike those pipe sections with a naturally bonded interface, there was no interfacial peeling between the pipe and the lining within the pipe sections where the interface was pinned. The nailed pipe sections at the interface only led to failure of the specimen due to excessive cracks. The cracks at the top and bottom of the pipes at the time of damage are shown in Figure 11c,d, with crack widths of 2.73 and 2.33 mm, respectively. The failure mode of specimen S-3 (bonded plastic film) is shown in Figure 12, and the crack width is shown in Figure 13. In Figure 12, it can be seen that when the displacement reached 1.32 mm, the load reached 10.71 kN. At this time, cracks appeared on top and the left arch line of the pipe, while two cracks appeared approximately 135\({}^{\circ}\) clockwise from the  
Figure 11: Schematic diagram of the crack width of interfacial nail-implanted pipe sections: (**a**) Top pipe cracking; (**b**) bottom pipe cracking; (**c**) top pipe crack at the time of damage; (**d**) bottom pipe crack at the time of damage. Figure 10: Damage form of an interfacial nail-implanted pipe section: (**a**) Cracking; (**b**) sabotage. top of the pipe. At the same time, the left and right interfaces peeled off and the cracks were measured, as shown in Figure 13a,b. The crack widths were 0.61 and 0.38 mm, respectively, and the interfacial bonding effect failed. At this time, the ultimate load was reached. As shown in Figure 13a-d, the crack widths on both sides of the pipe sections were 0.88 and 0.55 mm, respectively, when the ultimate load was reached. Because the interface peeled off at this time, the crack propagation speed was slow and its width was small. Due to the failure of the interfacial bonding, the lining layer could not play a bearing role, resulting in a lack of further improvement of the bearing capacity during the later stage of loading, and the cracks continued to expand.