PSI - Issue 78

Antonio Cefalì et al. / Procedia Structural Integrity 78 (2026) 1350–1357

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involving bridges must carefully consider the type of landslide and its kinematic and triggering mechanisms to ensure an efficient and functional system for emergency procedures. Continuous monitoring of natural slopes impacting bridges can serve multiple objectives, including controlling instability evolution and managing the safety of existing structures (Cheng and Lau, 2014; Simeoni et al., 2020). For tunnels, similar principles apply, with a focus on monitoring ground deformations, lining stresses, and groundwater conditions. The dynamic interaction between the tunnel structure and the surrounding ground during seismic events makes real-time monitoring of paramount importance (Finno and Calvello, 2005). This includes the use of extensometers, inclinometers, and pressure cells to track displacements and stress changes, as well as piezometers for monitoring groundwater levels. The "Observational Method" in geotechnical engineering provides a framework for integrating monitoring into the design and construction process (Nicholson et al., 1999; Sakurai et al., 2003). This iterative approach allows for continuous control during construction, monitoring, and review, enabling adjustments to be made as actual conditions are observed (Todaro, 2014). This method is particularly effective for underground structures, excavation fronts, and unstable slopes, where ground conditions can evolve progressively during construction. 3. Geotechnical monitoring of road retaining structures Road retaining structures, such as retaining walls and reinforced earth structures, are critical components of road infrastructure, particularly in mountainous or geologically unstable areas. Their stability directly impacts road network safety and functionality. Monitoring of these structures often involves assessing lateral earth pressures, deformations, and groundwater presence. Traditional instruments like inclinometers (Alatza et al., 2024) are widely used to measure horizontal displacements in the ground behind retaining walls, indicating potential instability. Extensometers can monitor movements normal to the wall face, while load cells measure forces on tie-backs or anchors. In addition to traditional methods, innovative techniques like distributed fiber optic sensors can provide continuous, real-time measurements of strain and temperature. Satellite-based Interferometric Synthetic Aperture Radar (InSAR) (Alatza et al., 2024; Balbi et al., 2021; Bru et al., 2024; Molan and Lohman, 2023; Refice et al., 2000) can detect millimetric surface deformations over large areas, useful for regional monitoring; Corner Reflectors (CRs) (Sarabandi and Chiu, 1996) can enhance InSAR measurements. Designing monitoring systems for retaining structures must consider specific failure mechanisms and prevailing geotechnical and seismic conditions, particularly the dynamic response to ground shaking. Systems should capture both static and dynamic deformations and pressures. In Italy, "Piani Stralcio per il Rischio Idrogeologico" (PAI) documents often mandate instrumental monitoring for interventions compatible with hydrogeological risk, especially for road structures in landslide stabilization or risk reduction projects. This implies a detailed monitoring plan specifying instrumentation, measurement frequency, and alert thresholds is often a mandatory design component. Continuous monitoring, combined with a clear response plan, allows for timely intervention and adjustment of mitigation measures — a proactive approach crucial for preventing catastrophic failures Road embankments and trenches are extensive earthworks crucial for road networks, whose stability is paramount, especially in seismically active or hydrogeologically vulnerable areas. Geotechnical monitoring of these features aims to detect deformations, internal instability, and environmental impacts. For embankments, monitoring often focuses on settlement, lateral spreading, and slope integrity. Instruments like settlement gauges, inclinometers (Alatza et al., 2024; Simeoni et al., 2020), and extensometers measure movements. Piezometers are vital for pore water pressures, as elevated pressures can reduce shear strength. Remote sensing, including terrestrial laser scanning, drone-based photogrammetry, and InSAR (Azadnejad et al., 2024), provides detailed topographic data and detects subtle geometric changes. For trenches, monitoring primarily concerns slope stability, rockfall potential, and groundwater seepage. Key indicators include face deformations, rock mass discontinuities, and tension cracks, tracked by extensometers, crack gauges, and tiltmeters. Geophones and seismic arrays can detect microseismic activity. Visual inspections, often augmented by robotic systems or drones, remain fundamental. Monitoring system design must account for site characteristics, seismic forces, and climatic factors. The "Observational Method" (Nicholson et al., 1999; Todaro, 2014) is highly applicable, allowing for adaptive management and optimization based on actual measurements, and ensuring the long-term safety and resilience of road infrastructures. 4. Geotechnical monitoring of road embankments and trenches