Measurement of Water and Air Permeability in Unsaturated Soil

Abstract

Abstract Equipment developed for the measurement of oil and gas flow in oil producing sands was used to study unsaturated permeability in a soil. The method employs the simultaneous flow of air and water under the same pressure gradient to maintain a uniform tension and, as a consequence, a uniform saturation within the sample during permeability measurements. The saturation is reduced in increments by reducing the water pressure with respect to the air pressure. Results of unsaturated permeability measurements on two relatively undisturbed samples of a sandy soil are presented. The interrelationship between gas and liquid permeabilities as a function of saturation is discussed, and a method of calculating the unsaturated water permeability from the more easily measured air permeabilities is suggested. The magnitude of gas slippage in a dry soil sample was determined by measuring the air permeability at several mean pressures and extrapolating the air permeability‐mean pressure function to an infinite pressure. The permeability to water of the saturated soil was only about half the permeability to air of the dry soil even when the air permeability was corrected for slippage.