Influence of Compactive Efforts on Bagasse Ash Treated Black Cotton Soil

Abstract

The paper presents the results of a laboratory study on the influence of three compactive efforts, (i.e., British Standard Light, BSL, West African Standard, WAS and British Standard Heavy, BSH) on the strength properties of treated black cotton soil. The tropical black clay was treated with a maximum 10% bagasse ash by weight of dry soil and the results show that the strength properties of the soil-bagasse ash mixture increased with higher compactive effort. The maximum dry densities (MDD) of the natural soil for BSL, WAS and BSH compactive efforts are 1.75, 1.91 and 2.05 Mg/m3, respectively. Treatment of natural soil with stabilizer gave peak values of 1.83 Mg/m3 at 10 % bagasse ash for BSL, 1.9 Mg/m3 at 8% bagasse ash for WAS, and 2.1 Mg/m3 at 2% bagasse ash for BSH compactive energy. The unconfined compressive strength (UCS) for the natural soil for the BSL, WAS, and BSH compactive efforts are 120, 355, and 424 kN/ m2, respectively, while the treated soil gave peak values of 229 kN/m2 at 10% bagasse ash for BSL, 469 kN/m2 at 6% bagasse ash for WAS and 756 kN/m2 at 8% bagasse for BSH compactive effort. Peak California bearing ratio (CBR) values for the BSL, WAS, and BSH compactive energies for the natural soil are 3, 6 and 8%, respectively, while values for treated soil are 8 at 10% bagasse ash for BSL, 11% at 2% bagasse ash for WAS and 13% at 8% bagasse ash for the BSH compactive effort. The WAS compaction energy which is conventionally used in the region yielded CBR value of 11% at 2% bagasse ash treatment of soil is recommended for use as subgrade of lightly trafficked roads in view of expected increase in strength due to time-dependent pozzolanic reactions. Keywords: California bearing ratio, Compactive effort, Unconfined compressive strength, British Standard Light, West African Standard, British Standard Heavy, Maximum dry density and Optimum moisture content. Nigerian Journal of Soil and Environmental Research Vol. 7 2007: pp. 92-101