Effect of Fines on Hysteretic Hydraulic Conductivity of Unsaturated Soil

Soil cover systems such as capillary barriers and compacted covers experience cyclic drying and wetting induced by evaporation and infiltration. These wetting and drying cycles have hysteretic effect on hydraulic properties of unsaturated soils. Numerous studies on hysteresis in soil water characteristic curve (SWCC) have been reported in the literature but only a limited number of studies deal with hysteretic unsaturated permeability of compacted sand-clay mixtures. In the present study, a series of laboratory permeability tests have been carried out to investigate the effect of fines on hysteretic hydraulic conductivity of unsaturated soil. The coefficient of unsaturated hydraulic conductivity of sand-kaolin mixtures containing 0%, 10%, and 30% kaolin by dry weight was determined for both drying and wetting cycles. A modified triaxial apparatus was used to apply suction and hydraulic head to measure the unsaturated permeability at different values of matric suction. Test results show that the hysteresis effect on permeability increases considerably with an increase in fines content in sand-clay mixtures.