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.