Field-monitoring and numerical investigation of a super-large-diameter shield tunnel undercrossing existing metro tunnels

Abstract

The Beiheng Expressway in Shanghai was built using a super-large shield with a diameter of 15 m, and its construction impact on adjacent underground structures cannot be overlooked. This newly built tunnel undercrossed Shanghai Metro Line 18 with a minimum distance of 7.86 m. Noticeable additional movements induced by the crossing can be observed in both lines according to in-situ data, initially manifested as slight settlement followed by atypically pronounced heave. The maximum uplifts of the up and down lines reach 7.23 and 5.09 mm, respectively. Subsequently, a numerical study was conducted on this crossing case, and its effectiveness was verified using in-situ data. The results revealed- the soil-structure interactions during the crossing period. The displacement curves in the longitudinal direction of the metro tunnels exhibited asymmetry owing to the oblique crossing, with greater deformation occurring in the region that was crossed earlier than in the region crossed later. Significant heave was also observed for the newly built segmental linings and surrounding ground, indicating pronounced floating induced by large-diameter excavation, which in turn caused the existing metro lines to move upward simultaneously.