Restricted salt diffusion in a geosynthetic clay liner

The influence of semipermeable membrane behaviour on salt diffusion through a geosynthetic clay liner (GCL) was investigated by conducting multi-stage membrane tests on four GCL specimens at different effective stresses (sigma' = 34.5-242 kPa) in flexible-wall cells. Each test was conducted by circulating five source potassium chloride solutions, sequentially from lowest to highest concentration (C-o = 3.9, 6.0, 8.7, 20.47 mM), across the top specimen boundary, while circulating de-ionized water across the bottom boundary. Membrane efficiency coefficients (v) were determined from differential pressure measurements, and effective salt-diffusion coefficients * (D-s(*)) were inferred from boundary electrical conductivities. Increases in D-s(*) with increasing C-o were observed for all specimens and were correlated to decreases in omega. In each case, D-s(*) decreased linearly toward zero as v. 1, regardless of the applied sigma'. These results support the hypothesis from pore-scale physical modelling that D-s(*) for GCLs exhibiting membrane behaviour may be expressed as a linear function of the quantity 1-omega.