Fikre (PhD), HenokKemal, Abdirshkur2018-06-082023-11-112018-06-082023-11-112015-11http://etd.aau.edu.et/handle/12345678/250Among the clay soils in the world, expansive soils have a special mineralogical characteristic which leads to swelling when exposed to moisture change. This behavior is due to the presence of considerable amount of montmorillonite clay mineral. As a result of swelling, pressure is exerted by the soil on the structures built on it and causes an increase in volume of the soil mass which also lifts the structure.Civil engineering structure constructed on such soils experience damage due to uneven movement caused by swelling and shrinkage process of the soil. It is known that the magnitude of the swelling of expansive soils varies with environmental conditions. In this study, the correlation between index properties and swelling pressure (Ps) of expansive soil found around Koye area are examined. The data of samples were obtained from 19 samples out of 12 test pits in Koye area. By taking those 19 disturbed and undisturbed samples from 12 test pits; both index properties and Swell-consolidation test were conducted according to ASTM standard. Then identification, classification and correlation between index properties and swelling pressure of the soil for the study area has been developed. The test results showed that the Specific Gravity ranges from 2.67 to 2.84. The index property test showed that plasticity index ranges from 56.23 to 70.26%, liquid limit ranges from 90.37 to 113.31%, plastic limit ranges from 34.57 to 43.06%, and liquidity index range from -0.08 to 0.21. The clay content of the soil is from 56.59 to 72.48%. Free swell tests conducted on the collected samples showed a range from 95 to 217.5%. The undisturbed sample test results showed that the swelling pressure of the area ranges between 80 and 400 kPa, ϒdry/ϒ’ ranges between 1.57 and 1.79 and moisture content range from 37.17 to 46.14%. According to the Unified Soil Classification System, the soil is categorized as Fat clay with a potential of expansion. AASHTO Classification System also shows that the soil is Plastic Clay with high volume change capacity. The new formulas are developed, by taking one or more of the five parameters (liquid limit, moisture content, plastic limit, dry density/effective, liquidity index and plastic index) in different combinations. The equations are developed by using SPSS 20 for windows software. Among the equations, equation 6 (Ps= 965.22 + 38.53*ϒdry/ϒ’ – 26.99*ω + 8.68*PL) which describes the relation better than the others is proposed. Finally, conclusions and recommendations are made.enGeotechnical EngineeringThesis