The use of fractal theory and soil index properties to infer the soil water retention curve for low and high plasticity clays

Abstract

Four fine-grained soils from South Australia containing differing particle size distributions were tested for their soil water retention properties. Despite their wide-ranging index properties, the samples from all four sites were confirmed to contain fractal particle size distributions (PSD) from sieve and hydrometer testing. Air entry values were obtained for each site from soil water retention curves (SWRC) that were generated using an unsaturated triaxial device with a pore air pressure/volume controller and a high air entry porous disk, which confirmed all sites contained fractal pore size distributions. The fractal dimensions of the particle and pore size distributions were not equal for any of the four sites tested in this paper. Using the four sites described in this paper, comparisons are presented between experimental SWRC results, theoretical results underpinned by fractal theory, and predictions derived from a curve fitting equation based solely on PSD and soil index properties. Lastly, this paper discusses the importance of understanding the unsaturated behaviour of fine-grained soils and some of the challenges associated with aligning current industry practice and advances in research within the field of unsaturated soil mechanics.