Multi-scale numerical modelling of tunnels intersecting large and active landslides

The interaction between landslides and transportation infrastructure represents a critical challenge in mountainous regions worldwide, intensified by demographic growth, infrastructure expansion into hazardous terrain, and climate change. Road tunnels appear particularly vulnerable as landslide frequency and intensity grow, yet comprehensive analysis remains elusive due to fundamental methodological limitations. This thesis addresses a persistent research gap in this field, termed the multi-scale challenge: the difficulty of simultaneously modelling large-scale landslide processes (extending hundreds of meters) and localized infrastructure damage (manifesting at centimeter scale) within computationally feasible frameworks. Existing approaches inevitably sacrifice resolution for one system component to maintain tractability for the other, oversimplifying either slope processes or structural response. To overcome this limitation, a comprehensive multi-scale modelling framework for landslide-tunnel interaction systems (LISs) was developed, adapting nested modelling principles to geomechanical and structural engineering applications. The approach explicitly separates spatial scales while establishing rigorous mechanical information transfer procedures. A coarse-resolution landslide-scale model captures bulk slope behavior and stress distributions, while a fine-resolution infrastructure-scale model focuses on detailed structural response, connected through systematic extraction and application of velocity fields and stress tensors. The framework is validated through application to the Passo della Morte landslide–San Lorenzo tunnel system (Carnian Alps, Italy): a 24-million-cubic-meter active rock-block slide moving 2–3 cm/year and affecting a 2200-meter tunnel serving as the area's sole transportation link. The landslide-scale model (FLAC3D) successfully reproduces observed displacement gradients confirmed by inclinometer and GNSS data. The infrastructure-scale model (3DEC) captures roto-translational deformation patterns, tensile stress concentrations at observed crack locations, and inter-segment joint behavior consistent with crackmeter measurements. This research demonstrates that nested modelling strategies can effectively address the multi-scale challenge while maintaining computational feasibility and physical accuracy, representing a solid methodological pathway toward evidence-based infrastructure management in landslide-prone regions.