STABILIZATION OF MEDIUM PLASTIC AND HIGH PLASTIC CLAY USING GYPSUM AND BAGASSE ASH

Abstract

Clays have a tendency to undergo volumetric changes on their interaction with water. These soils are a very common reason for most of the foundation failures due to their degraded properties like low shear strength, low bearing capacity, high shrink-swell potential and high compressibility. With the growing need of infrastructure development, avoiding these soils for future constructions is not possible. Engineering properties of these soils must be improved by chemical or mechanical means to meet structural requirements. The present research is intended to examine the effect of gypsum and bagasse ash on the properties of swelling clays and evaluate their potential use for the stabilization and improvement of engineering properties of these soils. Gypsum is naturally occurring mineral and bagasse ash is a waste product produced by sugar-mills. Two types of swelling clays, medium plastic, and high plastic clay, are used. Atterberg’s limits, compaction characteristics, unconfined compressive strength, California bearing ratio and swell potential of these soils are determined in untreated and after treatment with gypsum and bagasse ash. Soils treated with gypsum and bagasse ash exhibit a decrease in plasticity index and liquid limit, decrease in maximum dry density and an increase in optimum moisture content. Medium plastic clay had almost 6 times higher unsoaked compressive strength in treated form as compared to untreated form. While the improvement was around 27 times when tests were performed in soaked condition. High plastic clay exhibited 5.5 times higher unsoaked compressive strength than untreated soil while the improvement in soaked condition was around 30 times. Comparison of results between soaked and unsoaked strength tests results shows that the loss in strength due to soaking was much less in the soils treated with gypsum and bagasse ash as compared to untreated soils. California bearing ratio increased almost 3 times and one-dimensional swell potential also reduced to less than 1% changing soil nature to low swelling when these soils were treated with gypsum and bagasse ash. The improvement observed with the combination of gypsum and bagasse ash is more significant as compared to the individual effect of gypsum. The results indicate that gypsum and bagasse ash can provide an effective and economical method for the treatment of medium and high plastic clays.