Abstract
This paper focuses on the application of Advanced Satellite Synthetic Aperture Radar Interferometry (A-DInSAR) to subsidence-related issues, with particular reference to ground settlements due to external loads. Beyond the stratigraphic setting and the geotechnical properties of the subsoil, other relevant boundary conditions strongly influence the reliability of remotely sensed data for quantitative analyses and risk mitigation purposes. Because most of the Persistent Scatterer Interferometry (PSI) measurement points (Persistent Scatterers, PSs) lie on structures and infrastructures, the foundation type and the age of a construction are key factors for a proper interpretation of the time series of ground displacements. To exemplify a methodological approach to evaluate these issues, this paper refers to an analysis carried out in the coastal/deltaic plain west of Rome (Rome and Fiumicino municipalities) affected by subsidence and related damages to structures. This region is characterized by a complex geological setting (alternation of recent deposits with low and high compressibilities) and has been subjected to different urbanisation phases starting in the late 1800s, with a strong acceleration in the last few decades. The results of A-DInSAR analyses conducted from 1992 to 2015 have been interpreted in light of high-resolution geological/geotechnical models, the age of the construction, and the types of foundations of the buildings on which the PSs are located. Collection, interpretation, and processing of geo-thematic data were fundamental to obtain high-resolution models; change detection analyses of the land cover allowed us to classify structures/infrastructures in terms of the construction period. Additional information was collected to define the types of foundations, i.e., shallow versus deep foundations. As a result, we found that only by filtering and partitioning the A-DInSAR datasets on the basis of the above-mentioned boundary conditions can the related time series be considered a proxy of the consolidation process governing the subsidence related to external loads as confirmed by a comparison with results from a physically based back analysis based on Terzaghi’s theory. Therefore, if properly managed, the A-DInSAR data represents a powerful tool for capturing the evolutionary stage of the process for a single building and has potential for forecasting the behaviour of the terrain–foundation–structure combination.
Highlights
In the frame of geotechnical risks, subsidence is a relevant threat to human activities and urban settlements [1]
This paper focuses on the application of Advanced Satellite Synthetic Aperture Radar Interferometry (A-DInSAR) to subsidence-related issues, with particular reference to ground settlements due to external loads
We found that only by filtering and partitioning the A-DInSAR datasets on the basis of the above-mentioned boundary conditions can the related time series be considered a proxy of the consolidation process governing the subsidence related to external loads as confirmed by a comparison with results from a physically based back analysis based on Terzaghi’s theory
Summary
In the frame of geotechnical risks, subsidence is a relevant threat to human activities and urban settlements [1]. In the analyses of a single building or a neighbourhood (feasible thanks to high spatial resolution satellite images), in some cases a sort of badly organized pattern of displacement rates over the same structure is observed independently from the geological complexity of the subsoil This behaviour is caused by potential bias in the interpretation of the deformation, especially in terms of cause-and-effect relationships. The population of PSs, previously selected on a pure radiometric basis (i.e., signal amplitude and coherence), was split into subsets homogeneous in terms of structural features (foundation type) and class of construction age, which can provide a proxy of the “t0” of a consolidation process These derived datasets can be analysed to better understand and constrain the subsidence process, especially in terms of cause-and-effect relationships with the local geological setting (i.e., presence, depth, and thickness of compressible soil layers). From the perspective of quantitative applications, we compare the time series of selected PSs with the consolidation curves obtained by applying mono-dimensional Terzaghi’s theory
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