PNNL

Abstract

Natural soils are often anisotropic and the anisotropy in unsaturated hydraulic conductivity is saturation-dependent. A tensorial connectivity-tortuosity (TCT) concept was proposed to describe the unsaturated soil hydraulic property. The TCT concept states that soil pore connectivity and/or tortuosity are anisotropic and can be described using a tensor. The anisotropic hydraulic properties can then be described by extending the existing hydraulic functions, e.g., the Burdine (1953) and the Mualem (1976) models in such a way that the connectivity-tortuosity coefficient (L) is a tensor. The TCT concept was tested using synthetic Miller-similar soils with four levels of heterogeneity and four levels of anisotropy. The results show that the soil water retention curves were independent of soil anisotropy but dependent on soil heterogeneity. The TCT model can accurately describe the unsaturated hydraulic functions of anisotropic soils. The value of L is a function of both soil heterogeneity and anisotropy.