Accuracy Analysis of Convergence Monitoring in Twin-tube Shield Tunnels Using Mobile Laser Scanning

[Objective] Mobile 3D laser scanning technology is widely applied in single-tube tunnel monitoring due to its excellent measurement efficiency and high accuracy. However, the application of this technology for deformation monitoring in twin-tube shield tunnels is rare, necessitating analysis of the mobile 3D laser scanning accuracy for twin-tube shield tunnel deformation convergence monitoring. [Method] The feasibility of using this technology for convergence deformation monitoring in twin-tube shield tunnels is verified through accuracy validation. Point cloud data collected via mobile 3D laser scanning are processed using software parameter settings and segment ring correction to obtain convergence values, which are then compared with the convergence values measured by manual total station, thereby validating the accuracy of the mobile 3D laser scanning system. In addition, tunnel defects are analyzed by generating an unwrapped elevation view of the twin-tube shield tunnel. [Result & Conclusion] Based on a comparative analysis of 1 178 rings of measured data from a twin-tube shield tunnel on a rail transit line interval in Shanghai, it is found that: in both the first half and the second half of 2022, 90.66% of convergence changes in the twin-tube shield tunnel fell within the range of -1.0 to 1.0 mm, and 99.24% fell within -2.0 to 2.0 mm. The accuracy of the FARO S350 laser scanner in the twin-tube shield tunnel interval is 92.86% within -2.0 to 2.0 mm, and 99.58% within -3.0 to 3,0 mm. The field-measured data verifies the reliability of the mobile 3D laser scanning technology.