De Simone, Arianna (2025) Landslides in terraced cultural landscapes of the Mediterranean area: influence of agricultural practices and dry-stone walls’ efficiency on landslide hazard. [Tesi di dottorato]

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Abstract

The terraced cultural landscape of the Cinque Terre has experienced a marked acceleration in geo-hydrological instability phenomena over the last decades. This critical trend is attributed to a synergistic convergence of two primary factors: changes in the pluviometric regime, directly correlated with climate change, and the abandonment of traditional cultivation practices, which historically concurred to the balance between human activity and geomorphological slope processes. The resulting instability, which manifests as both large-scale collapses and localised failures of the dry-stone wall terrace systems, not only compromises land safety but also threatens the integrity of the landscape, which is recognised by UNESCO as a World Heritage Site. The stability of the terraced slopes of the Cinque Terre has been the subject of numerous scientific studies, which have mainly investigated the factors influencing the triggering of rainfall-induced shallow landslides at the basin scale. While these contributions have broadened knowledge on the resilience of these human-modified slopes using innovative methodologies for susceptibility assessment and post-event analysis, they highlighted a persistent gap in the literature. Specifically, there is a lack of studies that have analysed in detail and quantitatively the interrelationships between hydrological conditions, land use, and other influencing factors. A deep understanding of these dynamics is essential for accurately defining the factors driving slope instability and for developing effective and targeted mitigation strategies, which are crucial for counteracting the progressive degradation of this invaluable cultural landscape. To this end, the present study, using data retrieved from the "Stone Wall for Life" project's activities, aims at filling this gap by adopting a quantitative multi-scale approach to investigate the factors and conditions that influence the terraced slope stability, with a specific focus on the role of vegetation. The multi-scale methodological approach involved numerical modelling conducted on three experimental sites that exhibit varying land-use conditions (i.e., cultivated and abandoned scenarios). The study involved a preliminary stability analysis aimed at quantifying the influence of slope-scale stability factors through a shear strength reduction analysis. This preliminary analysis identified the characteristics of the material at the dry-stone wall foundation as an important controlling factor of the slope stability. Subsequently, the research proceeded towards a detailed local-scale investigation, focused on individual dry-stone wall terrace systems. To construct robust numerical models, in-situ hydrological and mechanical monitoring data collected in the frame of the "Stone Wall for Life" project were used. The models enabled flow analyses, stability analyses, and notably, coupled flow-deformation analyses. The flow analyses, integrated with stability analysis, allowed for the validation of the hydrological model and the definition of the factors regulating dry-stone wall stability and their relationship with the phases of the hydrological cycle (i.e. drying and wetting phases). The coupled flow-deformation analysis was fundamental for the validation of the mechanical model, enabling the comparison between numerically simulated horizontal stresses acting on dry-stone wall and those recorded in situ. This validation was essential for investigating the role of vegetation in terms of compressive stress regime that develops at the interface between the dry-stone wall and the backfill. The innovative aspect of this work lies in the analysis of the contribution of vegetation to soil stability, which was modelled exclusively through the increase in soil resistance produced by suction generated by plant roots following evapotranspiration process. The obtained results provided useful contributes for the definition of evidence-based landslide risk mitigation strategies.

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