Influence of exchangeable cations on hydraulic conductivity of compacted bentonite

Compaction and hydraulic conductivity tests were conducted using deionized (DI) water to determine how exchangeable cations affect the hydraulic conductivity of compacted bentonite. Regardless of the compaction pressure, the maximum dry density decreased and the optimum water content increased with increasing equivalent fraction of Na+ ions (XNa). The hydraulic conductivity decreased with increasing XNa. The initial dry density of bentonite generally had no effect on the hydraulic conductivity, regardless of the type of exchangeable cations. The hydraulic conductivity of bentonite decreased with increasing a final dry density. The decrease in hydraulic conductivity was more significant at higher XNa. The difference in hydraulic conductivity of the specimens at a given final dry density decreased with increasing a final dry density. When permeated with DI water, compacted Ca-bentonite with a very high dry density might have a very low hydraulic conductivity (< 10− 9 cm/s) similar to compacted Na-bentonite, if no volume change is allowed (i.e. very high effective stress).