Abstract
We present a methodology for the assessment of possible pre-failure bridge deformations, based on Synthetic Aperture Radar (SAR) observations. We apply this methodology to obtain a detailed 15-year survey of the Morandi bridge (Polcevera Viaduct) in the form of relative displacements across the structure prior to its collapse on August 14th 2018. We generated a displacement map for the structure from space-based SAR measurements acquired by the Italian constellation COSMO-SkyMed and the European constellation Sentinel-1A/B over the period 2009–2018. Historical satellite datasets include Envisat data spanning 2003–2011. The map reveals that the bridge was undergoing an increased magnitude of deformations over time prior to its collapse. This technique shows that the deck next to the collapsed pier was characterized since 2015 by increasing relative displacements. The COSMO-SkyMed dataset reveals the increased deformation magnitude over time of several points located near the strands of this deck between 12th March 2017 and August 2018.
Highlights
Over the past 20 years Interferometric Synthetic Aperture Radar (InSAR) and Persistent Scatterer Interferometry (PSI) have established themselves as a methodology capable of monitoring surface deformations in urban environments, thanks to the presence and density of coherent radar targets
While both the SNT and CSK descending datasets captured the temporal behavior of points located on the bridge deck, the SNT ascending dataset only recorded points located on the ground and for this reason has been discarded from our analysis (Figure 4 and Figure S2)
SNT descending scatterers located on the southern side of the balanced system 9 highlighted an area close to the junction between the southern west deck level and the southern west strand that was characterized by a motion toward the satellite at a rate of about 10.3 mm/yr and two deformation transient steps of 1 and 2 cm occurring on January 21st 2017 and April 28th 2018, respectively (Movie 3)
Summary
Over the past 20 years Interferometric Synthetic Aperture Radar (InSAR) and Persistent Scatterer Interferometry (PSI) have established themselves as a methodology capable of monitoring surface deformations in urban environments, thanks to the presence and density of coherent radar targets. We present a methodology for the assessment of single structure deformations, based on Synthetic Aperture Radar (SAR) observations and Markov Chain Monte Carlo (MCMC) approach. We applied this approach to the Morandi bridge producing a comprehensive multi-sensor time-series deformation map generated from space-based SAR measurements. We model the deformation inferred from multi-geometry observations using a MCMC approach to solve for three-dimensional deformation of the single decks and their base. We discuss the dataset records in light of their compatibility with possible collapse mechanisms, showing the potential operational use of InSAR millimeter accuracy time-series for early warning, hindcasting and forensic engineering applications
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