Evaluating alternative water content - Dry unit weight criteria for compacted clay liners

Three water content-dry unit weight (w-gamma(d)) compaction criteria for compacted clay liners (CCLs) used for waste disposal are evaluated with respect to laboratory-measured data for 13 clay soils being used for CCLs. The evaluation pertains to the ability of each of the criteria to accurately represent the hydraulic conductivity of the compacted clay soil as measured in the laboratory. Failure of a given criterion is based on soils that pass the criterion yet have hydraulic conductivity values greater than 10(-9) m/s. Based on this evaluation, the plastic limit approach (PLA) performs the poorest due to an inadequate correlation between the plastic limit and the optimum water context which is assumed in the PLA. The traditional approach (TA) and the line of optimums approach (LOA) provide reasonably similar results. The problems associated with the TA probably lire due to an inability to account properly for a reduced compactive effort relative to standard Proctor compaction (ASTM D 698). None of the soils failed any of the criteria when compacted using the modified Proctor compaction procedure (ASTM D 1557) illustrating the beneficial aspects of greater compactive effort.