Unsaturated hydraulic conductivity of compacted sand-kaolin mixtures

The unsaturated hydraulic conductivity of compacted sand-kaolin mixtures containing 0, 5, 10, and 30% kaolin (by dry weight) is measured for matric suctions, psi < similar to 6.0 m, The measured unsaturated hydraulic conductivity (k(measured)) values are compared with predicted unsaturated hydraulic conductivity (k(predicted)) values using the Brooks-Corey-Burdine and van Genuchten-Mualem relative hydraulic conductivity functions. In general, the accuracy of k(predicted) decreases with an increase in kaolin content or an increase in psi(m). In addition, k(measured) tends to be underpredicted for kaolin contents of 10 and 30% at relatively high suctions (1.0 m less than or equal to psi(m) less than or equal to 6.0 m) and overpredicted for kaolin contents of 0 and 5% at relatively low suctions (0.1 m less than or equal to psi(m) < 1.0 m), For a given kaolin content and psi, k(predicted) based on the Brooks-Corey-Burdine function tends to be more accurate than k(predicted) based on the van Genuchten-Mualem function. Finally, for 1.0 m less than or equal to psi(m) less than or equal to 6.0 m, k(predicted) based on analysis using the maximum volumetric water content (theta(m)) attained under steady-state flow conditions typically is more accurate than k(predicted) based on analysis using the saturated volumetric water content, theta(s), where theta(m) similar to 84-90% of theta(s) in this study.