Hydraulic conductivity and leachate removal rate of genetically different compacted clays

Abstract

Genetically different clays were compacted, contaminated and cured for 21 days with natural leachate from an old active waste disposal site and subsequently remolded at both West Africa (WA) and Modified AASHTO (MA) energies of compaction. The clays were thereafter investigated with a view to understanding the effect of contamination on hydraulic conductivity and mineralogy of the clays, soil–leachate interaction, influence of the energy of compaction and rate of leachate removal with time. Clay mineralogy revealed the presence of mixed clays including Anatase, Calcite, Hematite, Kaolinite, Quartz and Illite. The presence of these mixed clay minerals confers both attenuation and containment properties on the clays and, hence, makes the soils suitable for use as barriers in landfills. Hydraulic conductivity of the undisturbed and uncontaminated clays reduced with increase in energy of compaction from WA to MA. Leachate addition resulted in varied responses from the clays attributable to the different genealogy of the soils. Furthermore, the rate of leachate removal for the soils was observed to be 3.0 × 10-3 cm/s for SMP 1, 4.0 × 10-3cm/s for SMP 2 and 8.0 × 10-2 cm/s for SMP 5. These observations from the different soils are in agreement with results recorded in terms of consistency, hydraulic conductivity, mineralogy and compaction properties. However, influence of leachate on the structure of the genetically different soils played a contributory role in alteration of their mineralogy and, hence, their hydraulic conductivity.