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Evaluation of the Hydration Method of Geosynthetic Clay Liners in View of Subsoil ConditionsPresented study compares two hydration methods for geosynthetic clay liners (GCL) which were conducted through flexible-wall permeameters. In this study, GCLs were hydrated over silty sand and zeolite subsoils. At the end of the hydration durations, bentonite water contents from the control sample method (CSM) that uses two permeameters and the single large sample method (SLSM) that uses one permeameter were compared. There are 8% and 20% differences between the final bentonite water contents obtained from two methods when silty sand and zeolite were used as subsoil, respectively. Regardless of the hydration method used, bentonite water content of GCL hydrated over zeolite was two times greater than that of GCL hydrated over silty sand (~125% and 65%). In addition, subsoil water content profiles along silty sand and zeolite were quite similar. Although the final hydraulic conductivities of the GCLs hydrated with CSM and SLSM were almost the same, the hydraulic behaviors were different. This difference was caused by the water uptake of GCLs during the hydraulic conductivity tests. In contrast, although swelling of bentonite particles can be monitored more easily in CSM, this method is more expensive and troublesome than SLSM as it requires two parameameters and compacted specimens.

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The hydration performance of two geosynthetic clay liners (GCLs) over compacted zeolite is investigated in this paper. Zeolite was chosen as the subsoil because of its greater optimum water content with respect to other natural soils (41%). The water content changes of GCL-1 and GCL-2, which each had distinct properties, were the same until 30 days of hydration. The water content of GCL-1 increased from 120% to 147% after 62 days of hydration and then decreased to 117% after 90 days of hydration. However, the water content of GCL-2 was greater than that of GCL-1 (149% vs. 117%) after 90 days of hydration. The reduction in the water content of GCL-1 after 90 days was due to cation replacement. The exchangeable mole fractions of sodium cations (XNa) decreased whereas exchangeable mole fractions of divalent cations (XCa and XMg) increased with the duration of hydration. Cation replacement was more pronounced for GCL-1 than for GCL-2. Although swell indices decreased markedly with the durations of hydration, the final hydraulic conductivities of GCL-1 and GCL-2 were almost the same, around 2.0 × 10−11 m/s. This means higher water content masked the negative influence of cation replacement, resulting in comparable and low hydraulic conductivities for both GCLs.