Landslide Risk Management in Practice: Phased Mitigation Using the Observational Method

Landslide risk management typically involves an initial assessment to characterize the phenomenon and a subsequent phase to design and implement safety measures. However, financial constraints and technical challenges often require a phased approach to optimize resource allocation. In such cases, the observational method provides a flexible approach, allowing for phased implementation of measures while monitoring their effectiveness over time. In this study we applied this strategy to the "Paradisi" landslide (Belluno, Italy), a rotational slide at the interface between moraine debris and the Belluno Flysch formation.The 115x200 m landslideinvolves nearly 200,000 m3. Predisposing factors include poor geotechnical properties, high water content at the moraine-Flysch interface, and steep gradients, while intense winter precipitation triggers rapid mudflows along a central watercourse.Initial interventions addressed critical instabilities through slope reprofiling andshallow and medium-deep drainage systems. At the same time, monitoring systems - inclinometers and piezometers - tracked the slope behaviour. Subsequently, smart self-drilling composite anchors with optical fiber instrumentation were installed to stabilize the slope. Finally, the landslide toe was reinforced with a row of gabions spanning almost the entire width of the landslide. Drone-based photogrammetric periodic surveys complemented the monitoring efforts.This phased strategy allowed for iterative refinements, with each intervention evaluated based on observed residual movements and site conditions. The observational approach ensured that limited resources were effectively utilized.This strategy was applied not only to adaptively guide the phased course of action but also as a long-term framework to monitor future landslide evolution. This approach aims to assess the potential need for further risk mitigation phases, ensuring sustainable resource allocation and long-term site safety. The case study highlights the importance of integrating phased strategies with robust monitoring systems to optimize landslide risk management under resource constraints.