Correlation studies on index properties of fly ash-stabilised expansive clay liners

Abstract

The study of earthen barriers or clay liners has become very important in the field of geo-environmental engineering. The design of clay liners is based on the fact that leachate migration through clay liners depends on their hydraulic conductivity. The engineering behaviour of clay liners can be predicted through a proper estimation of some of the basic index properties like liquid limit which play a significant role in this study. An attempt at understanding the variation of index properties with the concentration of permeating fluids reveals useful facts about the clay liners. This paper proposes an innovative clay liner material in the form of fly ash-stabilised (or, fly ash-blended) expansive clay and presents a study on variation of index properties of the blend with varying fly ash content in the blend and concentration of salt solutions. The various permeating liquids used were deionised water and salt solutions such as CaCl2, NaCl and KCl. When expansive soils are stabilized with fly ash, index properties like liquid limit (LL) and swelling properties like free swell index (FSI) decrease; hydraulic conductivity also decreases because of a high dry density attained by the blend at increased fly ash contents. This paper presents experimental data on LL and FSI of an expansive clay soil stabilized with fly ash at 0%, 10%, 20% and 30% by weight of the expansive soil. The solution concentrations used in the test programme were 5 mM (or 5 milli Molar), 10 mM, 20 mM, 50 mM, 100 mM and 500 mM. LL and FSI decreased with increasing fly ash content in the blend and solution concentration for all the salt solutions. Useful correlations between LL and FSI for the salt solution concentration and the fly ash contents were obtained. Hydraulic conductivity decreased with increasing fly ash content in the blend and also with increasing solution concentration.