Comparative Study on Some Chemical and Mechanical Stabilizations of Expansive Soils

Abstract

This paper studies the differences between effects of chemical and mechanical stabilizations on the engineering properties of expansive soil. Undisturbed soil samples were collected form Abu-Gameem in South Sudan. The soil sample was very high expansive in accordance to the primary test conducted. Laboratory tests were undertaken to study the effect of chemical and mechanical additives individually on soil properties. Atterberg’s limits, compaction, California bearing ratio, free swell and swelling pressure tests were conducted on natural and treated soil. Quicklime was used as chemical stabilizer agent, while fine sand was used as mechanical. The lime was collected from Sabol industrial area in south of Khartoum while the sand was obtained from Omdurman in Sudan. The soil was first treated by quicklime contents as 3%, 5% and 7% by weight. Then separately was treated by fine sand contents as 5%, 10% 15% by weight. Comparing the results obtained from chemical and mechanical stabilizations, it can be reported that both of them are effective in improving the engineering properties of expansive soils. Notwithstanding, chemical stabilization improved the soil with less contents of additive. Addition of only 3% quicklime reduced soil plasticity from 45% to a suitable value (18%) while addition of 15% fine sand reduced soil plasticity to 24%. Addition of quicklime resulted in reduction of free swell index almost 4 times of its initial value, whereas slight reduction was observed when fine sand used. Significant improvement on the swelling pressure was obtained when using lime. But, the compaction characteristics were improved further when fine sand used. It could be concluded that based on the result of this study, chemical stabilization is more effective than mechanical. However, a combination of them can be used for further investigations.