Evaluation of the unsaturated hydraulic functions of compacted landfill clay liners: Impact on the predicted leakage rates

Various SWCC measurement techniques were evaluated. Three soil types (Soils 1–3), two compactive efforts (modified and standard), and two water contents (wet and dry of optimum) were used in this investigation. The predicted leakage based on the above conditions was investigated using the HELP model.; The pressure plate used in this study was shown to be problematic due to the continuous failure of the cellulose membrane. A new technique, the evaporation technique, developed in the current study provided an efficient alternative to the pressure plate in the SWCC determination. Samples prepared at wet of optimum had higher SWCC than dry of optimum water content samples. This trend was consistent for samples remolded using the modified and standard efforts. The SWCC for samples remolded using the modified effort plotted above the standard effort samples. This trend is consistent for the wet and dry of optimum water contents and for Soils 1–3. The SWCCs were arranged in the direction of decreasing plasticity. The factor with greatest impact on the resulting SWCC was Plasticity. The dynamic technique provided fully automated determination of SWCC. SWCCs from the dynamic technique plotted higher than the evaporation technique SWCCs for all the conditions studied. The trends of SWCC from the dynamic technique were similar to the trends obtained from the evaporation technique. Variations in the SWCC due to the measuring technique were greater than the Placement conditions or soil types. This variation was 26%.; A large scatter in the measured unsaturated hydraulic conductivity function was observed. This observation is in agreement with the results reported in the literature. Equations 2 and 3 fit the measured data reasonably well. However, Equations 4 and 5 did not fit the measured unsaturated hydraulic conductivity function.; The HELP model simulations showed that the predicted leakage was arranged in the direction of decreasing water content, decreasing compactive effort, and decreasing plasticity. In reality, these trends are reversed except for the water content. The condition with the greatest impact on the predicted leakage was the compaction water content. Compacting at wet of optimum water content resulted in 100% increase in the predicted leakage.