Influence of pore fluid concentration on water retention properties of compacted GMZ01 bentonite

Abstract

Due to its low hydraulic conductivity, high swelling capacity and good adsorption properties, the Gaomiaozi (GMZ) bentonite has been proposed as a suitable buffer/backfill material for the construction of artificial barriers in a deep geological repository for the disposal of high-level nuclear waste (HLW) in China. Compacted GMZ01 bentonite with an initial dry density of 1.70g/cm3 was hydrated with distilled water and NaCl solutions. The swelling strain was recorded. After being saturated, suction-controlled drying tests were conducted and corresponding soil water retention curves were obtained. MIP investigations were conducted on the void ratio variation of a specimen before and after experiencing wetting and drying processes. Results show that the swelling strain of compacted GMZ01 bentonite decreases as the concentration of infiltration solution increases. The shrinkage curve of saturated compacted GMZ01 bentonite specimens evolves with controlling suctions and could be divided into three stages including a normal shrinkage stage, a residual shrinkage stage and a zero shrinkage stage. For a given suction, the measured void ratio of a specimen saturated with distilled water is slightly larger than those of specimens saturated with salt solutions after the drying equilibrium is reached. For a given suction, the degree of saturation of a compacted GMZ01 bentonite specimen increases as the salt concentration increases. According to the test results, a modified SWRC equation was proposed to account for the effect of void ratio and salt solutions on drying behaviour. The verified results revealed that the proposed equation can satisfactorily describe the SWRCs of compacted GMZ01 bentonite saturated with different solutions.