Understanding the effects of tunneling on buildings by analyzing DInSAR data: The case of the new subway in Rome, Italy

Monitoring the displacements of the buildings during the execution of underground works is a very demanding activity in large urban areas contexts, due to the number of structures involved and to the duration of the measurements throughout the realization time. Therefore, the surface deformation detection cannot be based on direct measurements using ground-based sensors, only, and should include technologies that allow a systematic and comprehensive monitoring. The satellite DInSAR technique (Differential Interferometry Synthetic Aperture Radar) provides displacement time series of a large number of measuring points, which can be associated with different portions of a building and are able to reveal differential settlements. Furthermore, the availability of SAR data archived since 1992 allows performing back analyses to evaluate also long-term settlement processes not directly linked to the tunneling works. More recently, the COSMO-SkyMed constellation, developed by the Italian Space Agency (ASI), has provided data at higher space/time resolution, which have been profitably used to detect and follow the evolution of the settlements caused by tunneling excavation works, as in the case of the new metro line in Rome. By applying the advanced DInSAR methodology, we have estimated average rates of displacement for a number of buildings over the Metro C track interested by the subsidence, very likely triggered by tunneling. A classification-based approach was applied by taking into account the displacement rates and the associated statistical error parameters. This provided a tool for the direct identification of the most critical buildings that need further investigations.