Long-Term Longitudinal Deformation Characteristics of Metro Lines in Soft Soil Area

Metro lines buried in soft soil in coastal regions will inevitably suffer long-term uneven deformation during operation. In this study, the long-term deformation characteristics of metro lines in Shanghai soft deposits are analyzed based on extensive field data of four metro lines, i.e.,Shanghai metro lines (SMLs) 1-4. Settlement processes of complete lines and typical sections including both the tunnel and the station are illustrated. The cumulative longitudinal settlements of the four lines in 2008 and 2015 are presented and comparatively analyzed. The bending deformation process is analyzed and severe bending deformation is examined using the curvature radius and the relative deflection. All the extensive field data indicate that (1)SML 1 had the largest cumulative settlement and SML 4 showed the smallest cumulative settlement. The cumulative settlement is closely related to the time when the metro line was built. SMLs 1-4 settled before 2008 and uplifted entirely and slightly since then. (2)The deformation of the metro tunnel was gentle, whereas the deformation of the elevated metro line showed periodic fluctuations. (3)The bending deformation was more severe in the elevated metro line than those in the metro tunnel, although SML 3 was built later than SML 1. (4)Severe bending deformation appeared at the connections among the station and tunnel, tunnel entrance or exit, and side passageway. (5)The curvature radius was more suitable for examining the severe bending deformation of the elevated metro and the relative deflection was more suitable for examining that of the metro tunnel.