Improving Strength of Expansive Soil using Coffee Husk Ash for Subgrade Soil Formation: A Case Study in Jimma Town

Abstract

The economic back ground of Ethiopian mostly dependent of agricultural products. So that in the time of agricultural development production of large amount of wastes requires disposal. In order to reduce the disposal problem, utilization of waste in civil engineering works is very important aspect. Agricultural waste reuse has gained high momentum for achieving sustainable waste management in recent times. Keeping this view in mind this study has been carried out to assess utilization of coffee husk ash for improving expansive black cotton soil to utilize as a subgrade material for road construction. Hence experimental investigations have been made to study the suitability of coffee husk ash to improve properties of expansive soil. The important geo-technical properties test was Specific gravity, Liquid limit, Plastic limit, Plasticity index, dry density and California Bearing Ratio values. Expansive soil covers large portion of Ethiopia, covering nearly 40% surface area of the Country. Jimma town exhibits such kind of soil as a subgrade material. They are characterized by their nature of expansion or shrinkage upon changes in moisture content. According to ERA 2002 this type of soils is poor for subgrade construction. The laboratory work involved sieve analysis along with consistence test to classify the soil sample. The preliminary investigation of the soil shows that it belongs to A-7-5 class of soil in AASHTO and CH in USCS soil classification system. Soils under this class are generally of poor engineering use. Atterberg limits, compaction and CBR tests were used to evaluate properties of stabilized soil. The soil was stabilized with coffee husk ash in stepped concentration of 5%, 10%, 15%, 20%, and 25% by dry weight of the soil. Analysis of the results shows the addition of coffee husk ash improve the geotechnical properties of the expansive black cotton soil. The addition of Coffee husk ash reduces plasticity index, swelling and OMC with an increase in MDD and CBR with all increased coffee husk ash contents. The addition of 20% and 25% of coffee husk ash established an increased CBR value by 252% and 296% respectively, indicating the subgrade class falling under S3. From this study it was found out that coffee husk ash stabilized soil do meet the minimum requirement of ERA pavement manual specification for use as a sub-grade material in road construction. Agricultural waste like coffee husk Ash have significant potential to be used in place of conventional material for various road constructions and should be projected for future construction.