Unsaturated flow in anisotropic heterogeneous media: a centrifuge study

Abstract

Anisotropic and heterogeneous flow in unsaturated porous media is dependent on saturation conditions, and currently there exist limited options that adequately model this phenomenon. Herein, a modified unsaturated flow apparatus (UFA) and scaled centrifuge tests are used to investigate variations in unsaturated hydraulic conductivity. The method is used to find the unsaturated hydraulic conductivities for a layered system comprised of porous media with different hydraulic conductivities, which is tested under elevated levels of gravitational acceleration. The procedure is useful in reducing model size and test time, resulting in a feasible setup for laboratory scale experiments. Steady state volumetric water content is achieved under each pair of applied inflow rate and centrifuge speeds, allowing the determination of a corresponding unsaturated hydraulic conductivity. The setup also allows for rotation of the layered system for measurement of both vertical and horizontal hydraulic conductivities. The obtained values of hydraulic conductivity show a good fit to theoretical models and the degrees of anisotropy obtained are consistent with the literature. Overall, the results obtained using the modified unsaturated flow apparatus (UFA) indicate a great potential for further studying unsaturated hydraulic conductivity in anisotropic heterogeneous media, especially those with very low hydraulic conductivities.