PSI - Issue 84

Mirza Adeel Zeb et al. / Procedia Structural Integrity 84 (2026) 256–263

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The central and eastern sectors of the alluvial basin experience the most significant deformation, with vertical displacement rates ranging from -5 to -50 mm/yr. In contrast, the stable carbonate bedrock in the surrounding mountains shows negligible motion or slight uplift up to ±5 mm/yr (De Luca et al. 2022). The selected threshold exceeds the typical precision (±1–2 mm/yr) and reported accuracy of the PS-InSAR technique used by the EGMS (Crosetto et al. 2016 and Ferretti et al. 2001). Setting the threshold at ±5 mm/yr ensures that the identified structures have deformation rates that are significant and exceed the measurement system noise level, thereby enhancing the reliability and practical relevance of the screening results. Using the combined buffer-and-threshold approach, 16 bridges and viaducts were identified within active subsidence zones, all of which require further detailed evaluation. The spatial correspondence between the subsidence bowl and compressible Quaternary deposits highlights the dominant role of geological predisposition. EGMS data provide a high measurement point density, exceeding 500 points/km² in urban areas, ensuring comprehensive spatial coverage of the infrastructure network. 4.2. Identification of exposed bridges A vector geodatabase of 250 bridges was developed using provincial technical cartography. Notably, comprehensive assessment of the Caserta bridge network was previously conducted by Bencivenga et al. (2021, 2023) and Zizi et al. (2023). This study classified bridges by structural typology, geometry, construction materials, and age. In this study, each bridge was assigned a 100-meter buffer zone to define an area where ground movement could potentially affect the stability of its foundation.

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Fig. 3. Detailed view of a 16 critical bridges in the study area.

Zonal statistics were calculated using the decomposed vertical velocity raster within the defined buffer zones. Bridge exhibiting an average subsidence rate equal to or lower than -5 mm/yr were classified as exposed and flagged for further assessment. This spatial overlay combined with the zonal statistical analyses identified 16 bridges and viaducts within subsidence zones characterized by rates exceeding -5.4 mm/yr. Consequently, the remaining 234 bridges were not flagged for subsidence related concerns at this screening stage. The mean subsidence rates associated with these structures ranged from -5.5 to -10 mm/yr. Figure 3 highlights a critical cluster where a major bridge connection intersects a subsidence bowl with deformation rates lower than -10 mm/yr. The high density of EGMS measurement points on the viaduct deck, piers, and surrounding ground enables robust estimation of the measurement of displacement affecting the structure. European Ground Motion Service (EGMS) measurement points, color-coded according to vertical velocity, are overlaid on high-resolution satellite imagery. This figure illustrates the spatial resolution of the EGMS data, clearly showing persistent scatterers located directly on the bridges and viaduct structure within zones of high subsidence rates (deep red points).