Abstract: Soil-bentonite vertical cutoff wall is extensively applied to containment of urban industrial lands. Chemical compatibility of soil-bentonite backfill exposed to chemical solutions, i.e., hydraulic conductivity and its amplitude, is of importance to evaluate containment performance. Chemical compatibility of sand-bentonite backfill permeated with lead-zinc mixture (Pb-Zn), hexavalent chromium (Cr(VI)), and calcium (Ca) solutions was studied via flexible wall permeability test. The resulting hydraulic conductivity of the backfill permeated with Pb-Zn and Ca solutions considerably increases compared with the result obtained from uncontaminated specimen due to the squeeze of the double layer around bentonite particles. The hydraulic conductivity can not meet the requirement of anti-seepage when Pb-Zn concentration increased to 500 mmol/L. In contrast, limited increase in hydraulic conductivity is found when the backfill is permeated with Cr(VI) solutions. This is attributed to the fact that Cr(VI) exists in anionic complex rather than exchangeable cation. Predicting method for hydraulic conductivity of sand-bentonite backfills is developed based on the concept of bentonite void ratio and swell index of bentonite exposed to the corresponding inorganic solution.

Key words: bentonite, vertical cutoff barrier, inorganic salt, hydraulic conductivity, predictive method