The effects of salt solutions on the properties of bentonite-sand mixtures

The swelling behaviour and hydraulic conductivity of Na-bentonite powder an d bentonite-sand mixtures (10 and 20% of bentonite by dry weight) have been measured with distilled water and various salt solutions (0.01, 0.1 and 1 mol/l concentrations). It was found that in dilute solutions, the bentonite in mixtures subjected to small confining stresses swells sufficiently to s eparate the sand particles and reach a clay void ratio similar to that achi eved by bentonite alone. At high stresses, or in strong solutions, the bent onite in a mixture has insufficient swelling capacity to force the sand par ticles apart and swelling is limited by the sand pore volume. The hydraulic conductivity of a mixture depends on the bentonite void ratio, and the por osity and tortuosity of the sand matrix. A design model is proposed to pred ict the engineering properties of a mixture over a range of confining stres ses from the properties of its constituents and the permeant.