Effect of Sand Content and Plasticity on Swell and Hydraulic Behaviour of Expansive Soils

Abstract

Swelling and shrinkage of expansive soils raise concern over their performance for various geotechnical and geoenvironmental engineering applications such as top and bottom liners of landfills. Swelling results in heaving of expansive soil, whereas the shrinkage results in the formation of desiccation cracks. To overcome these volume changes in the expansive soils, they can be modified by adding sand which can reduce the swell potential and the formation of desiccation cracks. Plasticity, compaction, swelling and permeability characteristics of expansive soils get altered upon the addition of sand. In the present study, these characteristics of an expansive natural soil amended with sand and their interdependency with each other were examined through the experimental laboratory studies. Clay-sand mixtures passing through 2 mm sieve were prepared by thoroughly mixing the sand with expansive soil in three different proportions, namely low, medium and high sand content. Swell potential and hydraulic conductivity of different specimens under a surcharge load of 12.5 kN/m² were obtained from one-dimensional swell tests and rigid wall permeability tests, respectively. Although there was a considerable variation in the sand proportion added, the consistency limit tests showed only smaller reduction in liquid limit and plasticity index because of a lesser percentage of fine sand in the total sand added. In spite of the small changes in the consistency limits, a reduction of more than 50% in swell potential and increased hydraulic conductivity was observed, indicating the more significant influence of coarser non-swelling fraction on the swell and hydraulic behaviour of clay-sand mixtures.