A THESIS SUBMITTED TO THE GRADUATE STUDIES OF ARBAMINCH UNIVERSITY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF SCIENCE IN CIVIL ENGINEERING (GEOTECHNICAL ENGINEERING).

Abstract

Common problem with a series of challenges in Ethiopia is road pavement failure. The most likely cause of this failure is presence of expansive soil in the subgrade. The main objective of this thesis presents a study on identification of natural subgrade and improving compaction and CBR properties of expansive soil of Daye-Girja Road by using pumice in varying quantities. The experimental investigation was carried out for natural soil alone, and soilpumice mixes. A series of laboratory tests, such as moisture content, specific gravity, Atterberg limits, particle size distribution, free swell, compaction, and CBR tests, were conducted before and after adding pumice in (5%, 10%, and 15%) percentage by weight of expansive soil. The MDD values were increased, and OMC decreased with the addition of pumice. The optimum pumice content to stabilize expansive soil were taken as 15%. The plasticity index of the soilpumice treated sample after the curing periods of the first 21days 9.12%, 7.14%, and 5.43%, were obtained and California bearing ratio of 11.2%, 10.8% and 10.6% respectively obtained at 14 day curing period. And also, the results show that pumice provides better property improvement in term of liquid limit, plastic limit, plasticity index, compaction and California Bearing Ratio values are increased as pumice content increased with increasing pumice content. In general, stabilizing soil using 15% pumice content improves expansive subgrade soil, fulfilling sub-grade requirements and specifications of ERA manual and it is a costeffective than excavating and filling selected material