Anisotropy of Unsaturated Soils

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Abstract
A conceptual model is applied for quantitative evaluation of the anisotropy factor during desaturation. The soil is assumed to consist of many thin parallel layers having different hydraulic properties. A uniform density distribution function is used to represent the saturated hydraulic conductivity probability of the various layers. A power function relationship is assumed between the hydraulic conductivity and the capillary head. The exponent in the hydraulic conductivity‐capillary head relationship and the air entry value are allowed to be variables. The model indicates that the degree of anisotropy of unsaturated soil may vary considerably from its value at saturation. Reducing the capillary head gradually from zero, the anisotropy factor first decreases to a minimum and then increases rapidly as the soil dries. In some cases, the anisotropy factor can reach values several orders of magnitude higher than at saturation. Soil layers with very low permeability tend to diminish anisotropy on desaturation. Conversely, large variation of the hydraulic properties of the layers would enhance anisotropy in the unsaturated state.
Funding Information
  • David R. Bloom Center for Pharmacy, Hebrew University of Jerusalem

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