(A) STUDY ON PERFORMANCE IMPROVEMENT OF EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME EXPANSIVE SOIL USING RESIDUAL SOIL AND LIME

Abstract

The soils which show volumetric changes due to changes in their moisture content are referred to as expansive soils. With increase in moisture content, these soils swell and with decrease in moisture content undergo shrink. This leads to seasonal movements causing heave in rainy season and subsidence in summer, giving rise to high differential settlement in the structures founded on them thereby causing distress and damage to it. Stabilization of expansive soils with additives has been used with great success. In the recent past several investigations have been reported highlighting the beneficial use of lime for performance improvement of clay soils (Davidson and Handy, 1959; Thompson, 1966; Bhasin, 1978; Bell, 1988; Sivapullaiah et al., 1998, 2000; to name a few). In spite of these studies there is still need of further investigation to understand the mechanism of lime induced modifications of soils more clearly. From literature review it is observed that lime generally improves the performance of clayey soils in terms of reduced swelling and increased strength. However, in some cases, depending on the type of soil, amount of lime added, curing period etc. the performance improvement reduces. In view of this an attempt is made to carry out a systematic study through careful variation of above parameters, to develop an understanding of the mechanisms involved.Primarily an expansive soil (ES) and a residual soil (RS) that represent the extreme types of soil are used in the present study. The non swelling and high strength residual soil was added to the expansive soil to improve its performance. Besides to cover a wide range of plasticity these two soils are mixed in different proportion (i.e. 100%ES, 80%ES + 20%RS, 60%ES + 40%RS, 40%ES + 60%RS, 20%ES + 80% RS, 100%RS) to prepare six different soil samples. Subsequenty these soils were treated with lime of varied quantity under varied curing period. The test results indicate that the liquid limit continues to reduce till 3% lime content, beyond which the increased lime content has marginal effect on it. However, at very high lime content (i.e. 13%) and long curing period (i.e. 28 days) the liquid limit of the expansive soil has shown an increasing trend. This increasing trend gradually grows more prominent with increased percentage of residual soil and curing period. It is of interest to note that irrespective of soil type the liquid limit is large for increased curing period. The plastic limit increases with increases in lime content. The increase is relatively faster till lime content reaching about 3%. From 3 to 5% of lime content the rate of increase in plastic limit is relatively slow. Beyond 5% lime content visible increase in plastic limit is noticed only for increased percentage of residual soil and higher curing period. In general soils have shown an immediate decrease in plasticity index upon addition of lime. For 100%ES, increasing the lime content beyond 5% had a marginal effect in further reducing the plasticity index. This is in line with earlier observations that immediately upon addition of lime the liquid limit reduces and plastic limit increases. In general the plasticity index increases with increase in curing period however it is more prominent for the increased percentage of residual soil. This is attributed to the silica gel that enhances the...