Investigating deformation along metro lines in coastal cities considering different structures with InSAR and SBM analyses

The metro system solves traffic congestion in urban transportation while bringing potential deformation risks, especially in tunnels built in typical soft deposits in coastal cities. Time-series Synthetic Aperture Radar Interferometry (TS-InSAR) is an effective tool for monitoring land subsidence in urban areas. However, the different structures of metro lines, such as elevated tracks, ground lines, and tunnels, were often neglected in previous studies. Here, we introduced a Station Based Monitoring (SBM) method combined with InSAR analyses for metro safety monitoring. TS-InSAR provided the measurements along the elevated rails and ground lines. For tunnels, the TS-InSAR and SBM were jointly performed to deduct partial deformation under tunnels caused by land subsidence. The proposed metro system monitoring strategy was demonstrated and validated over the Shanghai Metro and Tianjin Rail Transit in the coastal cities of China. The results show that most deformed sections are located on the metro network's periphery, with velocities around −5 mm/year in Shanghai and −25 mm/year in Tianjin. The spatial distribution and temporal evolution of deformation characteristics along the two cases were then explored and compared. The proposed hazard matrix combining geological conditions and passenger density provided a more comprehensive assessment of potential hazards. The study highlights that InSAR and SBM analyses could be potentially applied to monitoring metro systems considering different structures