Three-Dimensional Modelling and Analysis of Slope Instability in Complex Geological Environments

This doctoral thesis presents an advanced methodological framework for the stability analysis of complex slopes, applied to the Montaguto landslide (Avellino, Italy), with a specific focus on the “La Montagna” sector. The research aims to overcome the inherent limitations of traditional two-dimensional modelling by adopting an integrated three-dimensional approach. The study begins with a rigorous geological and structural characterization, alongside a detailed geomechanical and geotechnical assessment of the materials, based on the interpretation of both in situ investigations and laboratory testing. The geometric complexity of the landslide body was modelled in Rhinoceros solid modelling software, enabling an accurate reconstruction of the computational domain by integrating high-resolution topographic surfaces with the intricate architecture of internal structural discontinuities. The core of the numerical analysis was the application of the FLAC3D (Fast Lagrangian Analysis of Continua) code. Using the Finite Difference Method (FDM), the software simulated the slope's stress-strain response. The kinematic analysis was coupled with an assessment of global stability via the Strength Reduction Technique (SRT). This procedure enabled calculation of the Factor of Safety (FoS) by progressively reducing the shear strength parameters (c, Φ), thereby allowing the onset and development of elasto-plastic failure mechanisms that are not constrained by predefined slip surfaces but are strictly dependent on the rheological properties of the interfaces. The research is further enriched by a section on the Maronti cliff (Ischia Island), where multitemporal photogrammetry was applied. Comparing multitemporal datasets enabled the quantification of volumetric changes and retreat rates, providing crucial empirical support for validating predictive models. In conclusion, this thesis demonstrates that combining digital monitoring methods with 3D numerical modelling enhances understanding of instability movements. The findings provide detailed insight into the evolution of the sites studied and suggest a practical protocol for hazard assessment and risk mitigation in complex geological settings.