Unsaturated Hydraulic Conductivity for Layered Heterogeneous Soils

This study investigates the effective hydraulic conductivities of unsaturated soils for one-dimensional structured heterogeneity. The heterogeneity is defined using homogeneous sublayers forming repeated unit cells. Results from previous studies indicated that for a large cell length, the effective hydraulic conductivity approaches an arithmetic average of the pressure heads which develop in each sublayer. For a cell of length approaching zero, the effective conductivity becomes the harmonic average of the individual sublayer hydraulic conductivities weighted according to the cell fraction each occupies. The effective hydraulic conductivity functions for the finite cell lengths fall within the envelope formed by the two limiting cases for small and large cell lengths. But the effective conductivity in previous studies was defined as the steady downward flow velocity for an infinitely deep profile. In this study, we examine the effective hydraulic conductivities for a finitely deep profile which is typical for many applications such as water fluxes for both infiltration and evaporation between ground surface and water table. We address the significance of profile depth, upper and bottom conditions in the profile on the effective hydraulic conductivities. The contrasting extent of the hydraulic parameters in the sublayers, which define the heterogeneity degree, and its influence on the effective hydraulic conductivities are also explored.