Laboratory Determination of Water Retention and Diffusion Coefficient in Unsaturated Sand

Abstract

Laboratory methods were presented to measure water retention and chloride diffusion coefficient in unsaturated medium sand. A tempe-diffusion cell was designed and disturbed and undisturbed methods were used in the experiments. In the disturbed method, new sand sample was used in each diffusion test and diffusion coefficient was determined based on the observed and predicted concentrations versus soil depth, and versus time in the source reservoir. In the undisturbed method, one sand sample was used throughout a successive diffusion testing with different suctions for sand in each test. The diffusion coefficient for each test was then determined based on the concentration versus time data in the source reservoir. There was a good agreement between the observed data and theoretical predictions in all experiments. The major advantage of the apparatus over other published methods lies in the fact that both the soil–water characteristic curve and ion diffusion coefficient at any degree of saturation, can be obtained on the same soil sample in a single suite of tests. These two parameters are required for several geotechnical and geoenvironmental engineering designs involving unsaturated soils, such as the solid waste landfills overlying natural or engineered layers of unsaturated granular soils.