Effective unsaturated hydraulic conductivity of layered sands

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. The averaged K(ψ) curves of the two homogeneous sands using a direct averaging approach were compared with the measured layered sand K(ψ) data. The result shows that the geometric mean of hydraulic conductivity‐suction curves of the coarse and medium sands approximates the measured hydraulic conductivity‐suction curve of the layered sand. The observed suction variance and effective hydraulic conductivity were compared with expressions developed from a stochastic theory. The results support the stochastic approach.