Multimodal land subsidence of the new reclaimed HKIA 3rd Runway from InSAR and independent component analysis

The three-runway system expansion project of the Hong Kong International Airport (HKIA) began with the land reclamation to the north of the original runway. Understanding its ground deformation is essential for subsequent civil construction and planning at the new land. Synthetic Aperture Radar Interferometry (InSAR) technique is firstly used to investigate the spatiotemporal characteristics of land subsidence after the completion of third runway pavement. Due to the consolidation of underlay materials, the third runway is subject to varying degrees of land subsidence, with the monitored maximum sinking rate to be ~100 mm/year during September 2021 to October 2023. We adopted the Independent Component Analysis (ICA) to separate the underlying sources in order to explore the spatiotemporal characteristics of deformation in the reclaimed land. The results show that there are three distinct deformation sources in the study area, including an exponential decay signal (an exponential decay consolidation process), a periodic signal (thermal effects correlated with buildings and bridges) and a linear signal (a continuous subsiding). Considering the different reclamation methods, the linear deformation component is mainly located in areas with prefabricated vertical drains (PVD), which is strongly associated with the overall subsidence pattern. On the other hand, the land reclaimed by Deep Cement Mixing (DCM) method tends to reach a stable state earlier than those reclaimed by the PVD method, demonstrating the effectiveness of the DCM in reinforcing the reclamations. These results benefit our understanding of the settlement process over the third runway of HKIA and provide reliable suggestions for follow-up reinforcement plans on specific locations if needed.