Compressibility and permeability characteristics of lead contaminated soil-bentonite vertical cutoff wall backfills

Soil-bentonite (SB) vertical cutoff walls are widely used in remediation of contaminated lands. The engineering properties of SB cutoff wall backfills will dramatically change due to their interaction with contaminants. However, investigation of the effect of heavy metals on the compressibility and permeability characteristics of SB backfills is very limited. A series of oedometer tests are conducted for kaolin-bentonite mixtures being potentially used as SB backfills. The soil samples are prepared with designed bentonite contents of 5%, 10%, and 15%, lead concentrations of 0, 5, 10, and 50 mg/g, and water content of approximate liquid limit. The results show that after lead contamination, the liquid limit, pH, specific surface area, compression index, and permeability coefficient of the soils considerably change regardless of the bentonite content. To further interprete the test data, the concepts of the generalized state parameter (e/e_L) and the void index (I_v) are adopted to evaluate the compression and permeability properties of the soils before and after lead contamination. The results suggest that e/e_L versus lg_p and/or lg_k, and I_v versus lg_p can be used as a useful engineering tool to characterize the compressibility and permeability properties of lead contaminated SB backfills. Finally, an empirical equation is proposed to generalize the permeability of the soils before and after lead contamination.