The results of confined swell, consolidation, and hydraulic conductivity tests on a needle-punched geosynthetic clay liner (GCL) are reported. The effects of permeant (distilled water, aqueous single salt solutions with concentrations between 0.01 and 2.0 M NaCl, and a synthetic municipal solid waste (MSW) leachate), static confining stress, hydrating medium, and degree of bentonite hydration at the time of the application of the confining stress are examined. Increases in the permeant salt concentration and decreases in the magnitude of the confining stress caused increases in the hydraulic conductivity. It is shown that high salt concentrations in the hydrating fluid increased the hydraulic conductivity. The GCLs permeated with 0.6 and 2.0 M NaCl solutions were more permeable than GCLs initially hydrated with water. The hydrating fluid was not as critical for permeation of 0.1 M NaCl. The effect of the degree of bentonite hydration at the time of the application of the confining stress was also found to be significant, highlighting the hydraulic benefits of maximizing overburden stress prior to GCL hydration. Tests performed using a synthetic MSW leachate gave results comparable to those obtained for aqueous salt solutions between 0.2 and 0.8 M NaCl. Practical implications are discussed.

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