Quantification of spatial heterogeneity and its influence on particle migration

Suffusion experiments were utilised to quantify the evolving degree of heterogeneity in gap-graded soils. Upward flow was imposed on test specimens comprising a mixture layer with varying finer fraction contents overlaid by a coarse layer. A coaxial permeameter cell enabled the local permeability to be obtained using spatial time domain reflectometry. Three methods (coefficient of variation, Dykstra-Parsons coefficient, and Lorenz coefficient) were employed to quantify heterogeneity based on spatial variability in local permeability. For the two-layered specimen in this study, all three methods demonstrated that suffusion had a homogenising effect with particle migration from the mixture layer to the coarse layer. Detailed insights were obtained from a multi-layered approach, where the Dykstra-Parsons coefficient was found to be more sensitive to spatial variations, while the Lorenz coefficient was less dependent on the amount of data. The key observation was that an increase in heterogeneity led to a reduction in particle migration. This is an important finding as prior studies focused on homogeneous specimens, while this study demonstrates that small amounts of heterogeneity can significantly impact particle migration characteristics. This reinforces the need to quantify the evolving degree of heterogeneity.