Laboratory investigation on stress-strain behaviour of cement-treated expansive soils

Abstract

This dissertation investigates an influence of non-swelling clay and cement contents on geotechnical properties of swelling soils. The Bangkok clay and bentonite were used as the non-swelling and swelling clays in this study. The swelling and non-swelling clays were mixed at different proportions. The 40:60 and 20:80 mixture clays were selected to be treated with 5% and 10% cement. It was found that engineering properties of expansive soils undergo favourable changes when mixed with a modest dose (20-40%) of non-swelling clays. However, a relatively large increase of non-swelling clay content is necessary to obtain markedly larger strength, stiffness, and CBR value, as well as reduce the shrink-swell properties. Correlations established among the untreated soil properties were tested against data from some previous study and found to be applicable satisfactory in most cases. On the other hand, while cement added to the mixture clays, the strength and stiffness of soils markedly increase along with a positively reduce of shrink-swell properties. In this study, a modified oedometer apparatus was developed to measure the vertical and lateral pressures, and then the lateral coefficient of swelling pressure can be defined. By adding cement to the swelling soils, the coefficient was markedly increased. It seems that the cement will affect to reduce swelling potential more in vertical direction. Hence, in the design of retaining structure on expansive soils, the engineer should aware the lateral coefficient of swelling pressure and the reduction of the lateral swelling pressure by considering the very rapid decrease of the vertical stress of cement-treated soils while compare that to untreated soils.