Anisotropy of unsaturated soils.

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.-from Author