Effect of Coating Defect, Desiccation, and Freeze-Thaw Cycles on Geosynthetic Clay Liner (GCLS) – Geomembrane Interface Transmissivity
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A series of laboratory tests were conducted to investigate the effect of prehydration fluid, a 4-mm diameter central coating defect, coating defect position and nature, and the effect of coating orientation of a multi-component coated geosynthetic clay liner (GCL) on interface transmissivity, θ between the interfaces of GCL and a 1.5mm thick high-density polyethylene geomembrane (GMB) when permeated with a simulated municipal solid waste landfill leachate. Also, two different conventional GCLs were used to explore the effect of prehydration and permeant fluid, desiccation of GCL on θ and assess the self-healing capacity of desiccated GCLs for three different permeant solutions under a range of applied stresses (10-150 kPa). It was found that < 70 kPa, θ was dominated by variability in initial contact condition between the interfaces of GMB-GCL and the effect of other factors was largely masked by the contact variability. At 100-150 kPa the effects of initial variability were largely eliminated but there was no notable effect of other factors for both multi-component and conventional GCLs. Desiccation of GCLs increased transmissivity by up to three orders of magnitude compared to an intact specimen at 10-100 kPa. Even at 150 kPa desiccated specimens had θ ≤ 8.0x10-9 m2/s for all specimens tested. The chemical composition of permeant solutions, crack width, and nature of bentonite played an important role in healing the cracks of desiccated GCLs. A new laboratory test setup was developed to apply freeze-thaw cycles at the GMB-GCL interfaces and tests were conducted to do a preliminary study of 5 and 16 freeze-thaw cycles effect, two different prehydration fluids and means of hydration of GCL during freeze-thaw cycles on θ, for a range of stresses (10-100kPa). The preliminary results showed that the new test setup successfully applied freeze/thaw cycles to the interfaces of GMB/GCL. The ice lenses, on thawing had a significant effect on θ at 10 kPa. When GCLs were externally prehydrated with RO water and pore water and then subjected to freeze-thaw cycles, there was no evidence of any significant effect of 5-freeze/thaw cycles but there was an effect of 16 freeze/thaw cycles on interface transmissivity.