Correlating Index Properties and Hydraulic Conductivity of Geosynthetic Clay Liners

TLDR

The study aims to assess whether liquid limit, sedimentation volume, and swell index of sodium bentonite GCLs can predict hydraulic conductivity for chemical compatibility evaluations. Index properties were measured on two sodium bentonite GCLs using deionized water and calcium chloride solutions, and hydraulic conductivity was determined under the same conditions to correlate the two sets of data. Higher calcium chloride concentrations lowered all index properties while raising hydraulic conductivity, with the liquid limit showing the strongest correlation; however, the relationship varied by bentonite quality and stress, and a critical threshold exists beyond which small decreases in an index property lead to more than tenfold increases in hydraulic conductivity.

Abstract

Three index properties (liquid limit, sedimentation volume, and swell index) of two sodium bentonites from geosynthetic clay liners (GCLs) are correlated with the hydraulic conductivity (k) of the same GCLs to evaluate the suitability of index properties for evaluating chemical compatibility. Deionized water (DIW) and calcium chloride (CaCl2) solutions were used for hydration (index tests) and permeation (hydraulic conductivity tests). In general, increasing the CaCl2 concentration caused each index property to decrease and the hydraulic conductivity to increase relative to values obtained with DIW, with the strongest correlations obtained with the liquid limit. The correspondence between index properties and hydraulic conductivity differed by index property, the quality of the bentonite, and the effective stress applied during the hydraulic conductivity test. Thus, correlations used for compatibility assessments are specific to the bentonite in the GCL and the stress conditions being applied. Results of the study also show that appreciable changes in hydraulic conductivity can occur with little or no change in index properties and that the greatest changes in index properties may correspond to conditions causing low or modest changes in hydraulic conductivity. However, in this study, a critical threshold existed for each index property, beyond which further decreases in an index property correlated with substantial increases (⪢10×) in hydraulic conductivity.