Monitoring of construction-induced urban ground deformations using Sentinel-1 PS-InSAR: The case study of tunneling in Dangjin, Korea

Abstract

The construction of underground tunnels can prime or trigger ground subsidence, and thus surface deformation monitoring is required during and post-construction. Freely available satellite data allow significant possibilities for the use of remote sensing techniques, particularly multi-temporal interferometric synthetic aperture radar (Mt-InSAR), for surface deformation monitoring. However, track records and field demonstrations of InSAR-based tunneling-related deformation monitoring are limited, particularly in identifying the spatiotemporal evolution of ground deformation and causal factors thereof from construction activities. Therefore, this study explores the feasibility of using satellite SAR data to monitor the surface deformation associated with different tunnel construction phases. Tunneling-related surface deformation was analyzed using the persistent scatterer InSAR (PS-InSAR) technique and Sentinel-1B SAR data; the PS-InSAR results were compared with those from the conventional leveling method. The velocity map of the study site revealed a localized subsidence trough asso-ciated with the construction of vertical shafts and shield tunneling. The cumulative time-series displacement map successfully tracked the spatial and temporal progression of ground deformations related to the phases of tunnel construction activities. The maximum subsidence rate in the radar line-of-sight direction was estimated to exceed 40 mm/yr, with maximum cumulative subsidence of ~ 200 mm. The results clearly showed that dewatering during tunneling aggravated the subsidence phenomenon. The consequent compaction and consolidation of the compressible soil layers due to the lowered groundwater table were the main causes of subsidence. Our results demonstrate the viability of the PS-InSAR technique based on the C-band Sentinel-1 product as a monitoring method to examine the spatiotemporal evolution of ground deformation patterns during tunneling activities and as a possible preliminary surveying tool to identify ongoing abnormal settlement prior to tunnel construction.