Long-term surface deformation and differential settlement assessment of an urban reclaimed land revealed by multi-sensor InSAR time-series analysis

Abstract Land reclamation in coastal regions presents geotechnical challenges, and continuous, site-wide monitoring of settlement can provide auxiliary information to support serviceability management once a site is operational. This study evaluates the 14-year spatiotemporal deformation of the H-Site within Cheongna International City, South Korea, by employing a multi-sensor InSAR framework (Sentinel-1 and Cosmo-SkyMed) integrated with machine learning-based scatterer refinement. By synthesizing geodetic observations with a network of ten geotechnical boreholes and daily groundwater monitoring, we identify a spatial disconnect between surficial reclaimed fill and subsidence magnitudes at the site. Pearson correlation analysis shows that the thickness of the deep natural sedimentary layer is correlated with both deformation velocity ( r = -0.58) and accumulated subsidence ( r = -0.54). In contrast, the thickness of artificial fill shows a weaker correlation with the same deformation metrics ( r = 0.18). The beginning of accelerated settlement in 2023 coincides temporally with intensive dewatering during an adjacent vertical shaft excavation in fractured weathered rock, consistent with groundwater drawdown as a trigger for the observed acceleration. These findings indicate that surface deformation at this reclaimed site is more closely associated with the deep sedimentary layer than with the shallow reclaimed fill.