Chemical Compatibility of Model Soil-Bentonite Backfill Containing Multiswellable Bentonite: Fid-Bau Portal

Chemical Compatibility of Model Soil-Bentonite Backfill Containing Multiswellable Bentonite

Malusis, Michael A. / McKeehan, Matthew D.

Abstract

The objective of this study was to evaluate the chemical compatibility of model soil-bentonite backfills containing multiswellable bentonite (MSB) relative to that of similar backfills containing untreated sodium (Na) bentonite or a commercially available, contaminant-resistant bentonite (SW101). Flexible-wall tests were conducted on consolidated backfill specimens ( $effective stress = 34.5 kPa$ ) containing clean sand and 4.5–5.7% bentonite (by dry weight) using tap water and calcium chloride (CaCl₂) solutions (10–1,000 mM) as the permeant liquids. Final values of hydraulic conductivity ( $k$ ) and intrinsic permeability ( $K$ ) to the CaCl₂ solutions were determined after achieving both short-term termination criteria as defined by ASTM D5084 and long-term termination criteria for chemical equilibrium between the influent and effluent. Specimens containing MSB exhibited the smallest increases in $k$ and $K$ upon permeation with a given CaCl₂ solution relative to specimens containing untreated Na bentonite or SW101. However, none of the specimens exhibited more than a fivefold increase in $k$ or $K$ , regardless of CaCl₂ concentration or bentonite type. Final $k$ values for specimens permeated with a given CaCl₂ solution after permeation with tap water were similar to those for specimens of the same backfill permeated with only the CaCl₂ solution, indicating that the order of permeation had no significant effect on $k$ . Also, final $k$ values for all specimens were within a factor of two of the $k$ measured after achieving the ASTM D5084 termination criteria. Thus, use of only the ASTM D5084 criteria would have been sufficient to obtain reasonable estimates of long-term hydraulic conductivity for the specimens in this study.