Early soil consolidation from magnetic extensometers and full resolution SAR interferometry over highly decorrelated reclaimed lands

Abstract

Abstract Reclaimed lands account for a large portion of the developable territories in Hong Kong. Towards better construction planning for the follow-up civil works, stability monitoring is usually required at these artificial sites. The Synthetic Aperture Radar Interferometry (InSAR) technique can provide bi-weekly updates of high resolution (up to 1\u202fm) and high precision (millimeter level) ground motion maps at low costs, which overcomes the limitations of ground-based instruments. However, rapid settlement during the early stage of soil consolidation can result in significant temporal decorrelation to phase signals and impact InSAR detection, especially over newly reclaimed areas. Here, we give a first demonstration on how the introduction of in-situ extensometer measurements can help improve InSAR capabilities for signal recovery of the early consolidation process. We integrate persistent scatterers (PS) and distributed scatterers (DS) in our processing chain to establish a two-tier monitoring network. Magnetic extensometers are used to estimate local consolidation models, which are then utilized to replace the linear part in the conventional functional phase model. For nonlinear deformation, both hyperbolic and exponential models were considered. The proposed method was applied to 61 TerraSAR-X images covering the Penny s Bay Reclamation Stage 2 (PBR2) in Hong Kong. The consolidation history of the new reclamation site has been successfully extracted, with cumulative subsidence exceeding 1.6\u202fm between May 2008 and Dec. 2011. Approximately 84% of the settlement of the non-dredged region was found to be from compaction of underlying soft marine deposits, not the filling materials. In addition to highlighting the spatiotemporal characteristics of the deformation, InSAR also helps reveal the compaction evolution of the underlying deposit. The results benefit our understanding of the early consolidation process in PBR2 and inform extra reinforcement plans if necessary.