Dynamics of Downslope Granular Flows and Impacts on Rigid Barriers: Effect of Particle Segregation

Abstract Understanding the flow dynamics of granular materials and their impacts on obstacles is crucial for disaster prediction and mitigation. Despite its importance, the effects of particle segregation on the flowability and impact behavior of granular flows remain insufficiently understood. This study addresses this gap by conducting numerical simulations to systematically investigate the influence of key factors—slope length, slope angle, and particle size—on segregation and granular flow behavior. The results indicate that segregation is more pronounced in the flow depth direction than in the flow direction, with the diameter ratio playing a critical role in driving segregation. Flow‐barrier interactions are shown to suppress segregation in granular flows. Moreover, particle segregation significantly impacts both peak and residual impact forces, with larger diameter ratios leading to greater impact forces on barriers and generating distinct pulse‐like features in the force profiles. Steeper slopes and longer flow lengths further amplify impact forces on barriers, while segregation changes the spatial distribution of these forces along the barriers. Segregation also influences the flowability of granular materials by inducing velocity differences between large and small particles, especially at the rear of the flow. The enhanced activity of large particles produces a U‐shaped flow depth profile, while small particles migrate downward during segregation. This downward migration causes small particles to act like rolling elements at the base, transforming the frictional interaction in the granular flow from sliding friction to rolling friction. This transition reduces frictional resistance, thereby promoting fluidization. These findings underscore the pivotal role of segregation in granular flow dynamics, offering some insights for engineering design and for understanding natural processes such as landslide runout distances, debris flow initiation, and the formation of depositional landforms.