## 4 Settlement Caused by Shield Tunnel Excavation
### Pavement Structure Stress for Different Tunnel Burial Depths  
During the tunnel excavation period, the ground surface settlement and pavement structure stress will change. In this paper, the finite element numerical model was used to investigate the pavement structure stress characteristics caused by the tunnel excavation under different tunnel burial depths. According to the distribution of pavement tensile stress, the pavement vulnerable areas were proposed for reference of pavement maintenance. Case 1: the tunnel buried depth = 46.5 m.  
The stress in the \(x\) direction of the runway in the transverse section when the buried depth = 46.5 m is shown in Figure 15. The pavement within 29.8 m of the shield tunnel axis was subjected to compressive stress. When the pavement was 56.5 m away from the tunnel axis, the stress basically dissipated to 0 kPa and the pavement 29.8-56.5 m away from the shield tunnel axis was subjected to tensile stress; the maximum tensile stress was 6.82 kPa. Case 2: the tunnel buried depth = 43.0 m.  
The stress in the \(x\) direction of the runway in the transverse section when the buried depth = 43.0 m is shown in Figure 16. The pavement within 28.1 m of the shield tunnel axis was subjected to compressive stress. When the pavement was 56.5 m away from the tunnel axis, the stress basically dissipated to 0 kPa and the pavement 28.1-56.5 m away from the shield tunnel axis was subjected to tensile stress; the maximum tensile stress was 8.56 kPa. Case 3: the tunnel buried depth = 30.0 m.  
The stress in the \(x\) direction of the runway in the transverse section when the buried depth = 30.0 m is shown in Figure 17. The pavement within 23.8 m of the shield tunnel axis was subjected to compressive stress. When the pavement was 56.5 m away from the tunnel  
Figure 14: Influence of buried depth on ground surface settlement. (**a**) settlement trough. (**b**) the relationship between maximum settlement and tunnel burial depth. (**c**) settlement development. Figure 15: Stress in \(x\) direction of runway in transverse section (the buried depth = 46.5 m). axis, the stress basically dissipated to 0 kPa and the pavement 23.8-56.5 m away from the shield tunnel axis was subjected to tensile stress; the maximum tensile stress was 76.10 kPa. Case 4: the tunnel buried depth = 22.5 m.  
The stress in the \(x\) direction of the runway in the transverse section when the buried depth = 22.5 m is shown in Figure 18. The pavement within 21.6 m of the shield tunnel axis was subjected to compressive stress. When the pavement was 56.5 m away from the tunnel axis, the stress basically dissipated to 0 kPa and the pavement 21.6-56.5 m away from the shield tunnel axis was subjected to tensile stress; the maximum tensile stress was 89.77 kPa. Case 5: the tunnel buried depth = 15.0 m.  
The stress in the \(x\) direction of the runway in the transverse section when the buried depth = 15.0 m is shown in Figure 19. The pavement within 20 m of the shield tunnel axis was subjected to compressive stress. When the pavement was 56.5 m away from the tunnel axis, the stress basically dissipated to 0 kPa and the pavement 20-56.5 m away from the shield tunnel axis was subjected to tensile stress; the maximum tensile stress was 95.01 kPa. Therefore, in the construction stage, the safety detection of this region should be considered to prevent the occurrence of runway cracks and other hidden dangers. Figure 16: Stress in \(x\) direction of runway in transverse section (the buried depth = 43.0 m). Figure 17: Stress in \(x\) direction of runway in transverse section (the buried depth = 30.0 m). After the completion of the shield tunnel excavation, the uneven settlement of the overlying pavement structure will occur, which will cause sudden changes in the bending tensile stress of the pavement structure, leading to structural damage.