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Water Relations of Saturated Bentonite: Some Effects of Temperature and Solution Salt Concentration¹

ABSTRACT

Transient flow (constant pressure desorption) and equilibrium pressure membrane experiments were used to determine some water relations of bentonite pastes in the range of water content (volume of water per unit volume of solid) from 6 to 33. The pastes were prepared in equilibrium with three different sodium chloride concentrations (3.25 m mol L^–1, 16.8 and 119 m mol L^–1), and the experiments were performed at temperatures of 277, 293, and 306 K. It was found that for each solution salt concentration, the moisture characteristic was effectively temperature independent, and the effect of solution concentration was qualitatively, but not quantitatively, in agreement with electrical double layer theory. In the transient flow experiments, both the cumulative outflow (expressed as a function of the square root of time) and the water content profiles (determined by destructive sampling and expressed as a function of material distance divided by square root of time) revealed clear temperature dependence. This effect is wholly accounted for by the temperature dependence of the kinematic viscosity of water. The observations lead us to infer that temperature dependence, over and above effects on viscosity, in the moisture characteristic and flow properties in unsaturated soils arises not in double-layer effects, but in effects on the air water interfaces in these systems.

¹ Contribution of CSIRO Divisions of Soils, and Water and Land Resources, Australia, and the Dep. of Soils, Water and Engineering, Univ. of Arizona, Tucson, AZ, USA.

² Chief, Division of Soils; Senior Research Scientist, Division of Water and Land Resources; and Professor and Head, Department of Soils, Water and Engineering, respectively.

Received for publication April 12, 1984. Accepted for publication August 14, 1984.