Integration of satellite monitoring and 3D modelling approach for multi-scale analysis of existing tunnel infrastructures

Existing tunnel infrastructures are increasingly exposed to external geomorphological processes and progressive structural degradation, highlighting the need for integrated monitoring approaches. This study proposes a multi-scale framework combining satellite-based interferometric data and high-resolution image-based inspections to assess the condition of existing tunnels. Interferometric Synthetic Aperture Radar (InSAR) analysis was used to detect and quantify ground deformation in the surroundings of two tunnel sites in Southern Italy, while three-dimensional (3D) reconstructions of tunnel linings were generated from high-resolution imagery acquired with a mobile system. The integration of both datasets was implemented in a 3D visualization environment, enabling the joint interpretation of external slope deformation and internal defect distribution. Results reveal deformation areas that spatially correspond to tunnel sectors showing defects, e.g., cracked joints and minor water seepages. Although the correlations are qualitative, the integrated analysis provided preliminary evidence of geomorphological control on tunnel degradation, particularly near the portals. The combined use of InSAR and very high-resolution images thus offered complementary perspectives, long-term surface monitoring and detailed internal diagnosis − within a unified georeferenced framework. This study demonstrates the potential of integrating remote sensing and digital inspection tools for preventive maintenance and risk assessment of existing tunnels, enhancing operator safety and minimizing highway closure. The proposed workflow represents a step toward a digital, data-driven approach to tunnel asset management, consistent with national regulations for infrastructure safety evaluation.