Stress-strain numerical investigation of climatic forcing on coastal landslide processes

Despite their relevance, coastal landslides have often been studied without distinguishing their evolutionary and triggering dynamics from those of their continental counterparts. The factors governing the predisposing, preparatory, and triggering phases of such processes are, in fact, rarely analysed within the specific coastal context in which these morphosculptures evolve. This gap is particularly evident in the limited use of numerical modelling approaches, which remain, to date, scarcely applied to the study of coastal instability processes. This doctoral research aims to investigate the mechanisms of selected coastal landslides in relation to specific climatic factors, adopting a multidisciplinary approach based on stress–strain numerical modelling techniques. Three distinct landslide systems were chosen as case studies, with the objective of analysing landslides that (i) are representative of different characteristics in terms of kinematics, rheology, and magnitude, (ii) exhibit different temporal patterns of evolution, and (iii) are influenced by distinct climate-related controlling factors. Specifically, a hydrodynamic model (Computational Fluid Dynamics – CFD), developed using OpenFOAM software, was coupled with a hybrid stress–strain numerical solution (Finite-Discrete Element Method – FDEM), implemented through Irazu software, to investigate the effects induced by meteorically driven weathering processes and by marine forcing acting on a soft tuffaceous cliff affected by small- to medium-scale rockfalls and topples occurring over short time spans (decades). Conversely, the role of eustatic standstills on the long-term (centuries and/or millennia) visco-plastic evolution of a lateral-spreading landslide system and of a composite soil landslide was analysed using a numerical solution based on the Finite Difference Method (FDM), performed with FLAC software. Some of the numerical analyses benefitted from data provided by an innovative monitoring system recently installed by the Department of Earth Sciences of Sapienza University of Rome, as well as from the results of radiocarbon (C14) and luminescence (OSL) dating analyses. The modelling approach developed here quantifies the relative contribution of long-term climatic predisposing factors, mid-term preparatory factors, and short-term triggering factors to the evolution of the analysed coastal landslide types. More specifically, the research results assess the influence of selected climatic factors on landslide evolution, highlighting how the considered forcings do not act independently, but rather within an evolving system progressively weakened by the local geological setting and rheological properties. The adopted multi-scale numerical solutions allow boundary climatic conditions to be translated into mechanical responses, thus providing a quantitative basis capable of evaluating the temporal hierarchy of landslide–climate interactions. Overall, the results underline both the potential and the limitations of the tested numerical approaches in studying the behaviour of climate-controlled coastal landslides, while also demonstrating their capability to analyse and simulate the main controlling factors governing the evolution of different coastal landslide systems across distinct temporal scales. When integrated with geomorphological and geochronological analyses and constrained by accurate data, this modelling strategy offers a physically consistent framework for quantitative hazard assessment and scenario forecasting in coastal environments.