Impact of Desiccation and Cation Exchange on the Hydraulic Conductivity of Factory- Prehydrated GCLs

Geosynthetic Clay Liners (GCLs) used in covers may be subjected to the adverse impact of desiccation coupled with cation exchange. Dense factory-prehydrated (DPH) GCLs have been introduced. Permeability tests alternated with drying phases were performed on a DPH GCL using distilled water (DW) and a 0.0125 M CaCl₂ solution. Mild and severe desiccations were simulated. The impact of dry/wet cycles on permeability was found to be limited even for severe desiccation with DW as hydrating liquid. Conversely, the hydraulic conductivity increased dramatically after a few cycles of severe desiccation using the CaCl₂ solution. Reduction of self-healing capacity caused by cation exchange appeared responsible for the increase in permeability. In case of partial desiccation, the permeability remained low for desiccation water contents higher than the prehydration water content (45%), and increased irreversibly for desiccation water contents lower than that of prehydration. Test results indicated that the permeability of DPH GCLs subjected to dry/wet cycles coupled with cation exchange strongly depends on the extent of desiccation; consequently, as conventional GCLs, DPH GCLs should be protected (e.g., by adequately thick surface layers) in covers where severe desiccation and cation exchange may occur.