Hydraulic Conductivity and Swell of Nonprehydrated Geosynthetic Clay Liners Permeated with Multispecies Inorganic Solutions

TLDR

The study examined how multispecies inorganic solutions influence swelling and hydraulic conductivity of sodium‑bentonite geosynthetic clay liners. A regression model was developed linking GCL hydraulic conductivity to the solution’s ionic strength and relative monovalent/divalent cation abundance. Results showed that higher ionic strength raises conductivity and reduces swell, whereas higher relative monovalent/divalent cation abundance raises swell and lowers conductivity, with these effects most pronounced at low ionic strength; a strong empirical relationship between conductivity and free swell was found, suggesting that high conductivities are unlikely for typical base liners but may arise with strong or polyvalent‑cation leachates.

Abstract

The influence of multispecies inorganic solutions on swelling and hydraulic conductivity of non-prehydrated geosynthetic clay liners (GCLs) containing sodium bentonite was examined. Ionic strength and the relative abundance of monovalent and divalent cations (RMD) in the permeant solution were found to influence swell of the bentonite, and the hydraulic conductivity of GCLs. Swell is directly related to RMD and inversely related to ionic strength, whereas hydraulic conductivity is directly related to ionic strength and inversely related to RMD. RMD has a greater influence for solutions with low ionic strength (e.g., 0.05M), whereas concentration effects dominate at high ionic strength (e.g., 0.5M). No discernable effect of cation species of similar valence was observed in the swell or hydraulic conductivity data for test solutions with similar ionic strength and RMD. A strong relationship between hydraulic conductivity and free swell was found, but the relationship must be defined empirically for a particular bentonite. A regression model relating hydraulic conductivity of the GCL to ionic strength and RMD of the permeant solution was developed. Predictions made with the model indicate that high hydraulic conductivities (i.e., >10-7cm/s) are not likely for GCLs in base liners in many solid waste containment facilities. However, for wastes with stronger leachates or leachates dominated by polyvalent cations, high hydraulic conductivities may occur.