Landslide impacts on built environment: Numerical analysis of the forces exerted by granular material collapsing on dry and submerged conditions

Landslide-generated impacts represent a critical hazard for coastal and reservoir infrastructures, yet their underlying fluid dynamics remain poorly understood due to the complexity of turbulent, free-surface flows. In this work, OpenFOAM® is used to investigate sudden impacts on surfaces caused by granular landslides. First, three sets of experiments are used to validate the numerical framework: a dry granular flow impact on a wall in an inclined flume, a debris avalanche impacting a pier and a dam-break interaction of a fluid impact on a vertical cylinder. For each case, numerical predictions are compared with experiments in terms of impact forces, providing confidence that the solver can reproduce sudden loads caused by granular and fluid masses. Then, the validated numerical setup is used to study submerged landslide impacts on slender cylinders, capturing the interaction between the granular slide and the free surface, resolving large-scale vortical structures and their role in energy transfer and dissipation. Results highlight two distinct stages of the phenomenon: (i) the initial impact and jet formation, and (ii) turbulent dissipation and recirculation. The analysis provides quantitative insights into velocity fields, pressure distributions, and turbulence intensities, and identifies key mechanisms driving energy loss. These findings contribute to a deeper physical understanding of landslide–impacts and offer a basis for improved hazard assessment and engineering design of protective structures.