Capillary Pressure-Dependent Anisotropy of Unsaturated Layered Soils.

The effects of saturation degree (or capillary pressure) on hydraulic conductivity anisotropy of unsaturated soils have been recognized for long time, but they have not been fully understood. The main objective of this study is to improve basic understanding of capillary pressure-dependent soil hydraulic conductivity anisotropy by examining how the anisotropy characteristics are related to the layered structure of soils. Specifically, we investigate the hydraulic conductivity anisotropy of layered soils bound by a same capillary pressure at both ends of the domain. Both randomly arranged layered soils and structurally heterogeneous soils of repeated unit cells of homogeneous sublayers are considered. The anisotropy is determined by the fluxes in vertical and horizontal directions subject to the same capillary pressure. The impact of various conditions is extensively examined and discussed. Results demonstrate that many factors such as capillary pressure, number and structure of the layers and correlations of layer hydraulic parameters significantly impact the anisotropy of unsaturated soils.