PSI - Issue 84

Lorenzo Brezzi et al. / Procedia Structural Integrity 84 (2026) 1159–1166

1160

1. Introduction The interaction between rapid landslides and linear infrastructures represents one of the most critical challenges in geotechnical risk assessment, particularly in mountainous regions where bridges and viaducts are frequently located at the base of steep and potentially unstable slopes. Rapid mass movements such as debris flows and rock avalanches are characterised by high velocities, short warning times and strong destructive potential, and may affect infrastructures through both direct impacts and indirect interaction mechanisms, including debris accumulation and impact on structural elements (Negi et al., 2020; Kumar et al., 2024; Brezzi et al., 2021a; Brezzi et al., 2021b). From an infrastructure engineering perspective, the assessment of rapid landslide–bridge interaction is particularly complex. Unlike slow-moving phenomena, which may induce progressive deformations and observable structural distress over long timescales, rapid landslides typically interact with bridges through short-duration, highly dynamic actions. These may involve impulsive loads acting on piers, abutments or foundations, as well as transient debris accumulation, and are therefore difficult to detect, predict and quantify using conventional inspection-based approaches. Recent analyses of bridge distress and collapse databases have highlighted the growing relevance of rapid landslide processes as a source of hazard for existing infrastructure networks, particularly in association with extreme meteorological events. Both national and international scale studies show that debris flows, rock avalanches and other rapid mass movements have contributed significantly to structural damage and, in several cases, to bridge collapse (Scala et al., 2025; Gabrieli et al., 2025). These findings emphasise the need for assessment tools capable of linking landslide propagation to physically meaningful estimates of the actions transferred to exposed structures. From a modelling standpoint, the evaluation of rapid landslide propagation and its potential interaction with infrastructures is affected by substantial uncertainty related to unstable volumes, heterogeneous material properties and highly nonlinear post-failure dynamics. Classical continuum-based numerical approaches are widely adopted for slope stability analyses, but they are not specifically conceived to handle the extreme kinematics and topological changes associated with rapid landslide propagation, where large displacements and fragmentation may lead to severe numerical limitations. To overcome these issues, particle-based and meshless numerical methods have been increasingly adopted over the last two decades to simulate large deformations and post-collapse dynamics. Among these, the Smoothed Particle Hydrodynamics (SPH) method, together with the Material Point Method (MPM) and the Particle Finite Element Method (PFEM), has been successfully applied to the modelling of rapid landslides and debris flows, owing to its ability to handle extreme deformations, free-surface evolution and complex solid–fluid interactions (Pastor et al., 2014; Han et al., 2019). Despite these advances, simulation results remain strongly affected by uncertainty in rheological parameters, particularly in the absence of site-specific calibration data (Van Westen et al., 2008; Brezzi et al., 2016; Cola et al., 2019). Under such conditions, deterministic analyses may provide a limited representation of landslide behaviour. Probabilistic approaches based on Monte Carlo sampling offer a more consistent framework to explore outcome variability and reduce user-dependence (Brezzi et al., 2021b). Within this context, the present study investigates the indirect interaction between rapid debris-flow phenomena and a highway viaduct located in a landslide-prone mountainous area of northern Italy, using SPH-based runout simulations coupled with Monte Carlo sampling of rheological parameters. The objective is to quantify the susceptibility of the viaduct to landslide involvement and to estimate the potential magnitude of impact forces acting on the structure under conservative assumptions. 2. Site description and historical instability context The analysed highway viaduct is located in a mountainous area of northern Italy, at the base of a steep rock slope characterised by widespread gravitational instability (Fig. 1a). The structure runs parallel to the slope toe, with limited horizontal separation between the abutments and the potential source areas of rapid landslide phenomena, resulting in a high exposure to indirect slope–infrastructure interaction mechanisms associated with rapid mass movements. The surrounding slope extends from approximately 610 m to 1380 m a.s.l. and is affected by a variety of instability processes, including rockfalls, topples and shallow landslides. The geological setting is dominated by Middle–Upper Triassic carbonate platform deposits, mainly dolomites and dolomitic limestones. In the lower sector of the slope (approximately 610–740 m a.s.l.), locally unfavourable dip-slope bedding conditions combine with slope gradients exceeding 40–50° and exposed rock faces. Upwards, slope inclinations locally exceed 55°, while a gently inclined