Stabilization of Black Cotton Soil with Lime and Animal Bone Ash for the Improvement of Subgrade Soil

Abstract

Black cotton soils are characterized by large volume change with changes in moisture condition. These characteristics of these soils resulted in the failure of highway pavement and civil structure. These soils cover about 40% of the area in Ethiopia. The engineering properties of such soils can be improved through stabilization. Therefore the aim of this study to investigate the stabilization of black cotton soil with lime, animal bone ash, and the mixture of both to improve the engineering properties of subgrade soil. Three black cotton soil samples were collected from different borrow pits in Konta-Ameya, the route called Chida, Ameya Cheka Bocha, and Ameya. Hydrated Lime was obtained from Sankale Lime Factory and bone samples were obtained in a fresh state from the abattoir (slaughterhouse) at Ameya town. The bone ash was prepared by calcination of the bone samples in a closed furnace at a temperature of 900°C for 8 hours. The research was done with the addition of varying content of stabilizers an increasing content of 0, 2, 4, 6, and 8% lime and 0, 2, 4, 6, and 8% animal bone ash each by dry weight of the soil, was used to treat the soil. Furthermore, a mixture of both by keeping 6% animal bone ash constant and varying lime content to 2, 3, and 4% by dry weight of the soil. For the analysis of the effect of the stabilizer on soil, a comparison was on the engineering properties of the native soil and stabilized soil. The comparison includes by carrying out: free swell, moisture content, grain size analysis, specific gravity, compaction test, Atterberg’s limit test, linear shrinkage test, California Bearing Ration (CBR) test, and swelling test on both the native soil and stabilized soil according to AASHTO and ASTM. The natural subgrade soils are A-7-5 according to the AASHTO soil classification system and CH as per USCS. Plasticity index of reduced from 59% to 13% at mix- the ratio of 6% BA + 4% lime. But adding BA in black cotton soil the plastic index decrease up to 6% BA then increases. The values for the MDD were noted to decrease with the addition of lime and mixture lime and bone ash content for reduced from 1.392 to 1.39 g/cm3 at mix- the ratio of 6% BA + 4% lime. And the OMC was found to increase from 28.52% to 30% at mix- the ratio of 6% BA + 4% lime. However, for bone ash alone up to 6% BA maximum dry density increase and moisture content decrease. the maximum value of CBR was achieved at 6% BA + 4% L was 7.56% and 8% lime value of 10.72%, 4.99% on the addition of 6% of BA with black cotton soil. The value of CBR decreases further in addition of BA percentage.it shows 6% BA + 3% L yields a similar result as the addition of 6% lime content. It is recommended that about 6% L alone and 6% BA + 3% L + 91 % S mixture could be used for the treatment of the soil to achieve a sub-grade material, thereby reducing the quantity (cost) of lime needed for stabilization and the environmental menace caused by the waste. It helps in reduction of the greenhouse of emission, as a result improved environment health.