Abstract

Debris flows (rapidly moving landslides consisting of saturated mixtures of soil, rocks and water) exist in nature as a particularly hazardous type of granular flow. Their motion involves complex interactions between particles and fluid that segregate in time and space. In order to better understand the modes of deformation of debris flows, we have carried out experiments that cover the physical extremes of behaviour. These involve, on the one hand, experiments on monodisperse particles under dry steady flow and on the other, fluid saturated physical models of unsteady debris flows that consist of particles of different size and shape. For the former experiments, we take measurements at the flow margins using Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) to enable flow profiles and granular temperature to be determined. For the latter, visual access to the internal processes is obtained by using “transparent soil”, Plane Laser Induced Fluorescence and PIV / PTV. The results provide insights as to the mechanisms that are of most importance to debris flow development and show that oversimplification may result in models that no longer reflect the prototype intended.