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 (σ′ = 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 (ω) were determined from differential pressure measurements, and effective salt-diffusion coefficients [Formula: see text] were inferred from boundary electrical conductivities. Increases in [Formula: see text] with increasing C o were observed for all specimens and were correlated to decreases in ω. In each case, [Formula: see text] decreased linearly toward zero as ω → 1, regardless of the applied σ′. These results support the hypothesis from pore-scale physical modelling that [Formula: see text] for GCLs exhibiting membrane behaviour may be expressed as a linear function of the quantity 1 − ω.