Three-dimensional deformations in transparent soil using fluorescent markers

This paper presents details of a new, simple and low-cost technique that allows three-dimensional (3D) movements of individual particles, and particle aggregations, to be observed in geotechnical physical model experiments. This has been achieved by seeding a transparent granular mass formed from sand-sized fused silica particles and a pore fluid with matching refractive index with crushed uranium glass particles, which do not significantly impact transparency. When illuminated by low-power lasers, the particles fluoresce and appear bright green, which greatly increases the sample's texture, and can be easily detected by photography. These tracer particles have been used to obtain two-dimensional soil deformations using both digital image correlation and particle tracking; and by using stereo-photogrammetry, 3D positions and displacements can also be analysed. Displacements were measured through 85 mm of the transparent model, and the technique should allow a single plane to be illuminated and measured at much greater depths. Fluorescent uranium glass tracer particles enable both individual glass particles and particle aggregations to be tracked. The stereo-photogrammetric system developed is shown to be a cost-effective and viable method of quantifying 3D deformations within a transparent soil model.