As dry blended polymer GCLs (DB GCLs) continue to gain popularity, it is important to understand the effect that hydraulic gradient can have on the hydraulicĬonductivity and polymer elution of these GCLs, in order to ensure that laboratory compatibility testing is applicable to field compatibility. The effect of hydraulic gradient on conventional Na-B GCLs has been studied extensively and shown to have a negligible effect on K values for gradients as high as 2500. Higher gradients are used because of the extremely long test durations associated with low hydraulic conductivity values of GCLs. Subsequent increases in K are hypothesized to partially result from elution of polymer from the pore space, which may be exacerbated from seepage forces associated with permeation at high hydraulic gradient.ĪSTM D5084 recommends using a hydraulic gradient less than 30 for materials with K values less than 1*10-7 m/s, while laboratory hydraulic conductivity testing procedures generally have much higher hydraulic gradients. The mechanism for decreased hydraulic conductivity (K) in these GCLs is hypothesized to be physical clogging of the intergranular pore space with polymer hydrogel. The layer of bentonite is held in place with some combination of adhesive, needle punching, or stitch-bonding.īecause of the susceptibility of Na-Bentonite GCLs to chemical incompatibility (e.g., increases in hydraulic conductivity) with aggressive (e.g., high ionic strength) permeant solutions, there has been a demand for chemically resistant GCLs, such as those composed of a dry blend of polymer and bentonite. GCLs are primarily comprised of a layer of processed sodium bentonite (Na-B), generally 7-10 mm thick, sandwiched between two geosynthetic fabrics or membranes. Geosynthetic Clay Liners (GCLs) were developed in the 1980’s as an alternative landfill liner or cover material.
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