THESIS SUBMITTED TO THE SCHOOL OF GRADUATE STUDIES OF ARBAMINCH UNIVERSITY IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SIENCE IN CIVIL ENGINEERING (GEOTECHNICAL ENGINEERING)

Abstract

Expansive soils are characterized by volume change due to variation in moisture content. The cyclic wetting and drying process causes vertical and horizontal movement in expansive soils leading to failure of civil engineering structures found on such soils. The failure on the structure resulted in economic loss. The problematic nature of such soils can be improved by replacing problematic soil with selected material and employing chemical stabilization techniques such as lime cement and enzyme stabilization. However, excavation and replacement of the problematic soil may lead to increase in project cost and time as it needs excavation of the problematic soil, production and transportation of the selected material and compaction to the required specification. In addition to the above, to get selected materials, additional borrow areas need to be excavated and that contribute a lot for environmental degradation. And also these techniques are expensive to developing countries such as Ethiopia , locally available low cost materials can be applied as alternative to improve the engineering properties of expansive soils. In the present research work, the performance of marble dust, lime and burnt brick dust were used to improve the problematic nature of expansive soils. The study is carried out on a highly expansive soil section of selected road project. The natural sub-grade soil obtained from the highly expansive section of the road is characterized for its engineering and strength properties and it is found to be highly expansive soil with low bearing capacity, high swell and characterized as A-7-5 according to the AASHTO classification and rated as poor (unsuitable) sub grade material. The expansive sub-grade soil is blended with increasing percentage by weight (5% to 20% lime and marble dust with fixed 10% brick dust) and the improvements in engineering properties are studied and it is noted that it improves with increasing percentage of marble dust and lime. With the higher percentage of marble dust and lime (15%) with (10%) brick dust, the swelling potential of the natural soil changed from ‘High’ to ‘Medium’, LL reduced from 105.57-109.16% to 51.1-62.5%, PI reduced from 68.1-70.83% to 30.6-36.4%, CBR increased from 4.1-4.39 % to 5.08-6.25% and also there is improvement on maximum dry density 1.24-1.32g/cm3 for natural soil to 1.38-1.55g/cm3 for stabilized soul. Thus, marble dust lime and brick dust can be recommended as an alternative stabilizing agent