Volume 21, Issue 4 (December 1998)
A New Apparatus for Measuring Oxygen Diffusion and Water Retention in Soils
A new apparatus developed for measuring the diffusion of oxygen, or any gas, through a soil sample is described. The apparatus uses nitrogen pressure to change a soil sample's degree of saturation and can therefore minimize the effects of structural changes due to remixing and packing. As a consequence, some innovative methods are employed to simulate oxygen concentration versus time data obtained with the apparatus. A one-dimensional semianalytic diffusion model is used to back-calculate diffusion coefficients based on laboratory data. Results for a local silt and a sand are presented to illustrate the utility of the apparatus. The apparatus is shown to perform well and provide gas diffusion coefficients similar to those reported by other researchers. The major advantage of the apparatus over other published methods lies in the fact that both the soil-water characteristic curve and oxygen 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 use of soil covers for mitigating acid drainage in sulfide-bearing mine waste.