Evaluating the hydraulic conductivity of GCLs permeated with non-standard liquids

Fundamental factors and testing considerations affecting the evaluation of the hydraulic conductivity of geosynthetic clay liners (GCLs) permeated with non-standard liquids (i.e., liquids other than water) are discussed and supported with test data. Both aggregate-size distribution and montmorillonite content of the bentonite portion of the GCL have a potential effect on the hydraulic conductivity of GCLs. Other factors affecting the hydraulic conductivity of GCLs permeated with non-standard liquids include thickness of the adsorbed layer, prehydration of the GCL, void ratio of the GCL, and test duration, Results show that non-standard liquids containing both high concentrations of monovalent cations (e.g., 0.6 M NaCl) as well as low concentrations of divalent cations (e.g. 0.0125 M CaCl2) can cause significant increases (greater than or equal to 1 order of magnitude) in hydraulic conductivity provided the test is performed sufficiently long to allow for exchange of adsorbed cations. Results also indicate that termination of hydraulic conductivity tests involving prehydrated GCLs before chemical equilibrium is established may result in measured hydraulic conductivities that do not represent equilibrium and may be unconservatively low, Finally, control of average effective stress is more important than control of hydraulic gradient when evaluating the hydraulic conductivity of GCLs. (C) 2000 Elsevier Science Ltd. All rights reserved.