Salt content impact on the unsaturated property of bentonite–sand buffer backfilling materials

Bentonite mixed with sand is often considered as possible engineered barrier in deep high-level radioactive waste disposal in China. In the present work, the vapor transfer technique and water infiltration apparatus were used to measure the soil water characteristic curve (SWCC) and unsaturated hydraulic conductivity (ku) of bentonite–sand mixtures (B/S) effected by salt content. Results show, the water-holding capacity and ku increase slightly with the concentration of Na+ in pore liquid increasing from 0 g/L to 12 g/L, similar with the solution concentration of Beishan groundwater in China. Salt content in the laboratory produced only one order of magnitude increase in ku, which is the “safe” value. The different pore liquid concentrations used in this study led to small differences in thickness of diffuse double layer of bentonite in mixtures, this might explain why some differences have been found in final values of ku.