Study on Deformation Control during Shield Tunnel Construction Beneath Existing Tunnels

This study is based on the background that the tunnel of Ningbo Metro Line 8 passes beneath the tunnel of Line 1. A three-dimensional numerical model was developed using Midas to simulate the deformation induced by the construction of the new Line 8 tunnel beneath the existing Line 1 tunnel. The results show that the maximum lateral horizontal deformation, longitudinal horizontal deformation, and vertical deformation of the Line 1 tunnel occur after the excavation of the Line 8 tunnel is completed. Notably, all deformations comply with the settlement control standards for existing tunnels in urban rail transit systems in China. After the excavation of the Line 8 tunnel is completed, the maximum surface settlement is less than the settlement control value, indicating that the excavation of Line 8 tunnel has less additional impact on the Line 1 tunnel. It is recommended that, during the construction of the new tunnel, intensive monitoring of the existing tunnel is implemented, particularly focusing on settlement in the central section, to mitigate the risk of structural damage due to excessive deformation.