Preliminary Studies of Hydraulic and Mechanical Behavior of Nanoparticle-Based Light Backfill Exposed to Pore Fluid Salinity

Abstract

Because of its high swelling pressure and low hydraulic conductivity, compacted bentonite–sand is widely accepted as a barrier/backfill material used in deep geological repositories to safely contain highly toxic radioactive waste. The majority of research conducted in this field shows that the pore fluid salinity present in the repository’s environment reduces the swelling capacity and increases the hydraulic conductivity of backfill material. However, research has yet to determine how to improve the material properties of backfill under saline water conditions. In this study, two different percentages of nanoparticles derived from bentonite (1 and 2% with respect to dry weight of bentonite) were carefully mixed with a bentonite–sand mixture to prepare a nanoparticle-based light backfill. Next, the effect of different concentrations of NaCl and CaCl2 on the hydraulic and mechanical behavior of a 50∶50 bentonite–sand mixtures was examined, at a maximum dry density of 1.24 Mg/m3. The results showed that CaCl2 solutions have more influence on material performance as compared to NaCl solutions. Additionally, results indicated that the presence of nanoparticles reduces the hydraulic conductivity and the rate of consolidation for saline-solution-saturated light backfill; however, no major improvement of swelling pressure was observed within the scope of this experimental approach.