Effect of NaCl Solution on Swelling Characteristics of Bentonite with Different Diffuse Double Layers

Abstract

Soil particles generally possess negative ions, and form an electronic field nearby the particles, which results in generating diffuse double layers on the surface of the particles. There is no diffuse double layer at dry state, and it develops diffuse double layers first when wetted by solution. This paper investigates the effect of NaCl solution on swelling characteristics of bentonite with different initial water contents by performing a series of wetting tests. The wetting test results indicate that when the initial water content is less than 10%, the NaCl solution has no effect on the swelling. When the initial water content is larger than 10%, the swelling strain decreases with increase in the NaCl solution concentration. The nuclear magnetic resonance (NMR) tests on compacted bentonite specimens were performed. The test results indicate that the strongly bound water content is 10%, which is similar to that by other method. The NMR tests on full wetting specimens, whose initial water content is less than 10%, show that the NaCl solution has no effect on NMR tests results. When the initial water content is larger than 10%, the proportion of curves from the NMR tests decreases with increase in the NaCl solution concentration. The NMR tests results indicate that the swelling occurred mainly in the intra-aggregate rather than in the inter-aggregate.