Direct measurement of unsaturated permeability of kaolin-sand mixtures

Abstract

Unsaturated permeabilities of six different kaolin-sand mixtures named as 100K0S, 90K10S, 80K20S, 50K50S, 20K80S, and 10K90S were directly measured using a modified flexible wall triaxial permeameter system. 90K10S means that the soil mixture contains 90% kaolin and 10% sand by dry mass. Soil–water characteristic curves (SWCC) of the kaolin-sand soil mixtures were also measured for a wide range of suctions using a Tempe pressure cell, 5-bar pressure plate, 15-bar pressure plate, and saturated salt solutions. The unsaturated permeabilities of the soil mixtures were also estimated using ten different theoretical models using (1) the measured SWCC data over a complete suction range and (2) the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values. The directly measured unsaturated permeability of the soil mixtures was used to validate the estimated values of unsaturated permeability. The results showed that the unsaturated permeability estimation models could reasonably fit the directly measured unsaturated permeability data when both the data from the complete measurement of SWCC and the measured SWCC data up to 100 kPa suction in combination with the estimated SWCC data at higher suction values were used.