Investigation of Lime Stabilized Expansive Subgrade Formation with Coffee Husk Ash: A Case Study in Jimma City in Kitto Furdisa Campus.

Abstract

Infrastructure development is one of the key player and backbone to sustain economic activities of every country. The stability of the infrastructures depends totally on the stability of the soil at which it rests. Our country Ethiopia consist of various types of soils in different areas as sandy, clayey, silts, granular soil, black cotton soil etc. Some of these type of soil are having poor bearing capacity which are not suitable to bear the structural load of road and have a significant influence on planning, design, construction, and maintenance. In order to improve these deficiencies, stabilization was used to enhance the bearing capacity of mentioned soil. This research focused on evaluating the effect of lime and lime-coffee husk ash used as a stabilizer on the expansive soil in Jimma city, JiT Campus. The sample used for this study was selected purposively composed of the expected sample size. This study majorly aimed at reducing the cost of soil stabilization in that the usage by considering the lime as control at constant percentage and CHA as cheaper alternative stabilizing agent by assessing the properties of soil free of agent and a mixture of soil and Lime, soil and Lime-CHA of varying amounts. The tests carried out on the properties of both natural and stabilized sample include; Atterberg limits, Specific gravity, Compaction, free swell index, linear shrinkage and CBR. Hence, experimental investigations have been made on natural soil and the sample was expansive in nature and classified as a heavy clay with 48% PI and 2.10% CBR value. Additionally, the study was continued using lime and coffee husk ash to improve properties of expansive soil. Initially, the sample was stabilized with lime at (4%, 6%, 8% & 10%). The results indicates that increasing the blending ratio of lime content reduced the PI of the soil up to 6% and started to increases and CBR value increased up to 6% and decreased at higher percentages. Moreover, the MDD value decreased while OMC increased similar to the other properties up to 6% and reversed as the content increased. Therefore, based on the test results, the optimum percentage of lime was investigated at 6% and the researcher used 5% of lime as a control even though the result was within the range of ERA requirement for subgrade soil by saving 1% for further investigation and blending with coffee husk ash at various percentages. Thus, 5%L and varies percentage of CHA mixes (i.e. 5%, 10%, 15%, 20%, and 25%), were investigated and, it improves all the properties at 5%+20% CHA, which fulfilled the ERA subgrade soil requirements. Therefore, it was recommended by the researcher to use 5% Lime + 20% CHA as the percentage of stabilizing agent for the subgrade soil.