3D deformation analysis in a metropolitan area during ongoing subway construction using time series InSAR

Unprecedented urban development poses significant subsidence challenges, primarily attributed to underground construction activities. Conventional approaches for monitoring these underground operations can be cumbersome. Therefore, time-series InSAR techniques emerges as a promising approach to quantify these deformations with high spatio-temporal details. However, distinguishing subsidence from city-scale deformation patterns often presents difficulties. Additionally, most previous studies concentrated on vertical deformation neglecting horizontal motions, thus hinder the comprehensive understanding of deformation dynamics. Lastly, the monitoring of deformations during ongoing subway construction has rarely been conducted. Therefore, this study employed PS-InSAR techniques to integrate Sentinel-1A ascending and descending datasets over the period from 2018 to 2023, with the aim of comprehensively extracting 3D deformation patterns, incorporating both vertical and horizontal components. Automatic methodologies were employed to distinguish the deformation caused by groundwater fluctuations and subway construction. The robustness of the results was statistically validated using geodetic leveling datasets. The results of the case study revealed vertical and horizontal deformations, with the vertical component being more prominent. Within the vertical deformation zones, localized horizontal deformations were evident due to their abrupt directional shift, albeit with a lesser magnitude. Persistent uplift was identified through East-North-Up (ENU)-derived vertical deformation at the rates of 8.04 and 6.85 mm/yr, respectively, in the test area. Long-term groundwater rebounds were observed, corresponding to a 1 mm uplift for every 1 m rise. The maximum cumulative subsidence recorded was 1 mm at the G07 MRT station, well within safe allowable limits. The findings are grounded in methodological advancements that hold the potential for comprehending deformation patterns on a global scale. Consequently, a much comprehensive and efficient monitoring of the ground deformation of a subway construction project can be achieved by employing the proposed approach.