Effects of NaCl solution on the swelling and shrinkage behavior of compacted bentonite under one-dimensional conditions

Because of its low hydraulic conductivity, high swelling capacity, and good adsorption properties, Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for construction of artificial barriers in deep geological repositories for high-level nuclear waste (HLW) disposal in China. By varying the concentration of NaCl solution and total suction, the swelling and shrinkage characteristics of compacted GMZ bentonite were studied under one-dimensional conditions. Results show that the swelling strain of compacted GMZ bentonite decreases as the concentration of NaCl solution increases under one-dimensional conditions. During drying with suction control by vapor phase technique, the density increases with suction. Simultaneously, the sample saturated with salt solution has a larger void ratio than that of the sample saturated with distilled water under the same suction. The void ratio and water content of the samples decrease with increasing suction. For a given suction, the sample saturated with salt solution has a higher degree of saturation than the sample saturated with distilled water. With the obtained water content (w), void ratio (e), and the degree of saturation (S-r), soil-water retention curves (SWRCs) were calculated for samples initially hydrated with different concentrations of NaCl solution. The SWRCs reveal that the sample with salt solution has higher water retention capacity than the sample with distilled water. A modified SWRC equation was proposed to account for the effect of NaCl solutions on the drying process of compacted GMZ bentonite under one-dimensional conditions. The results confirm that the modified SWRC equation can effectively describe the SWRCs of compacted GMZ bentonite considering the effects of NaCl solutions.