Hydraulic Conductivity of Unsaturated Specimens of Lateritic Soil-Bentonite Mixtures

Accurate evaluation of unsaturated hydraulic conductivity (K unsat ) is critical in ensuring the reliability of the waste disposal structure. In this study, hydraulic conductivity of unsaturated specimens of compacted lateritic soil blended with bentonite at 0, 2.5, 5, 7.5 and 10% concentrations was determined by the Brooks & Corey-Burdine (BCB) and van Genuchten–Mualem (vGM) relative hydraulic conductivity expressions. The soil–water characteristic curve (SWCC) fitting parameters were obtained by the pressure plate procedure for all the formulated mixtures. Soil mixtures for the experiments were prepared at − 2, 0 and + 2% of optimum moisture content (OMC) using British Standard heavy, (BSH) compaction effort. Predicted K unsat of soil mixtures decreased nonlinearly with matric suction (ψ) from 6.44 × 10 –9 to 5.9 × 10 –15 m/s while the K unsat at the three moisture conditions decreased with higher compaction water content. As with K sat , the effect of the bentonite treatment was significant, with K unsat of treated specimens recording orders of magnitude lower than those of the natural soil. The disparity between predicted K unsat by the two models was almost negligible and agreed reasonably well with measured results in documented studies indicating that the models used could provide reasonable estimates or patterns of K unsat of the mixtures.