Models for water retention and unsaturated permeability in full range of water content

The existing models for water retention and unsaturated permeability are successful at higher water contents but often give poor results at lower water contents. The water retention curve can be divided into capillary and adsorption segments by a dividing point, where the residual volumetric water content is assumed to vary with the matric suction, which can improve the applicability of Van Genuchten model to range of lower volumetric water content, and further extend it to the full range of volumetric water content. In addition, a permeability model for film flow in an even spherical particle assembly is modified by introducing a correction factor. The total unsaturated permeability is then considered to be the sum of those due to capillary and film flows. The two modified models are then verified using the test data of water retention and unsaturated permeability at higher and lower volumetric water contents for six loams in the existing literatures. The results show that the two modified models mach the measurements of water retention and unsaturated permeability better than the traditional models in the full range of volumetric water content.