Internal imaging of saturated granular free-surface flows

This paper presents a novel method to investigate the internal behaviour of saturated granular free-surface flows in the context of high-speed movement. Such an approach aims to study the motion of the solids and fluid within the flow in small-scale model flume tests with a view to better understanding debris flows mechanics. Through the employment of a particular solid, liquid and fluorescent dye and the application of an optical technique that relies on precise matching of refractive indices, the arrangement and re-arrangement of the grains within the fluid can be determined by way of planar laser-induced fluorescence. The adopted methodologies, together with the physical and optical properties of the selected fluid and solid phases, are described. The results of a series of experiments performed in a small laboratory flume are presented. The results show the effectiveness of this technique and the reliability of an artificial glass-oil mixture in reproducing the key features of flows composed of natural materials.