Measurements of permeability of saturated and unsaturated soils

The management and engineering assessments of geotechnical assets within the national transportation inventory require an appropriate knowledge of permeability of saturated and unsaturated soils. Determination of the permeability of saturated soils can be carried out using direct measurements, whereas that of unsaturated soils is often made using indirect methods based on the soil water retention curve. In this study an attempt was made to develop a novel approach for measuring the saturated and unsaturated permeability of soils. The tests were conducted on 100 mm dia. reconstituted and compacted samples of glacial till. Suctions were generated by circulating low-humidity air through a slender sand column located at the centre of the samples. Measurements of suction were made by two tensiometers located radially at the base of the samples. The drying process was terminated when the observed suctions reached or approached the limiting capacity of the tensiometers (1500 kPa). Combinations of suction measurements and volumetric strains during the drying process were used to determine the permeability by adopting analytical solutions as applicable to a radial flow condition

Development of a laboratory technique for obtaining Soil Water Retention Curves under external loading in conjunction with high capacity tensiometers

This paper reports the development of a testing chamber and an improved and reliable laboratory procedure capable of establishing soil water retention curves under triaxial stress conditions. The system provides the ability to take soil samples through multiple wetting–drying cycles in conjunction with measurements of suction and volumetric variables. Four drying and wetting tests were carried out on samples of glacial till and kaolin to validate the testing chamber and the associated procedures. Significant desaturation of soil samples was limited by the measurement capacity of the tensiometers. The system sustained high values of suction for a prolonged period of testing involving a sequence of drying and wetting. Suction was generated by circulating less humid air through the middle of the soil sample, which in effect generated suction gradients along the radial directions. Consequently, this had some impact on the interpretation of the volumetric variables