The effective hydraulic conductivity of unsaturated layered sands

Abstract

Accurate estimates of field-scale hydraulic conductivities of unsaturated heterogeneous soils are very difficult to obtain. In the present study, various approaches to determining effective conductivity values for heterogeneous sands are compared with laboratory measurements. The unsaturated hydraulic conductivity, K(Ψ), of two homogeneous sands and one layered sand composed of the two homogeneous sands was measured using the steady-state flux control method. A van Genuchten model and an exponential model were fitted to the data. Various means of the homogeneous sand fitted K(Ψ) curves were compared with the layered sand K(Ψ) data using a direct averaging approach. The observed suction head variance, effective hydraulic conductivity, and the anisotropy were compared with expressions developed from stochastic theory. The results qualitatively support the stochastic approach. The outcome of the direct averaging approach was inconclusive however. Additional laboratory and field experimentation is needed.