IMPROVING CHARACTERISTICS OF EXPANSIVE SUB-GRADE SOILS ON ROAD SECTION BY USING AGGREGATE DUST (CASE STUDY OF ARBAMINCH TO GERESSE ROAD)

Abstract

Road pavement failure is becoming a common problem with a series of challenges in Ethiopia. The most likely cause of this failure is expanding soil in the subgrade. Low shear strength, high compressibility, and plasticity characterize this type of soil. To improve the properties of this soil; reinforcement and/or stabilization methods are commonly used. The soil in the Arbaminch to Geresse road project does not meet the subgrade soil specifications, so work is being done to remove the original soil and replace it with selected material. This comes at an additional cost, may displace the people, and change the landscape of the area. This study aimed to investigate the strength characteristics of reinforced expansive sub-grade soil by using Aggregate dust to be used as a sub-grade road. The experimental programs were carried out for natural soil alone and soil-Aggregate dust. A series of laboratory tests, such as moisture content, specific gravity, Atterberg limits, particle size distribution, free swell, compaction, and CBR tests, were conducted. The percentage of aggregate dust by mass of dry soil was 5%, 10%, and 15%, and 20% was taken. Using 5% to 20% aggregate dust on two test pits, the OMC decrease from 42.15% to 17.05%, and 37.55% to 18.89%, respectively, while the MDD increases from 1.29g/cm3 to 1.78g/cm3, and 1.46g/cm3 to 1.83g/cm3. The CBR value increased to 20% of aggregate dust content but it fulfills minimum requirement by 15% then 15%aggreget dust is selected as optimum percentage for the soil-aggregate dust mix. The MDD and CBR values increased and OMC decreased with the addition of Aggregate dust. The maximum CBR values from tow pits, 5.08%, and 5.41% were obtained at 15% aggregate dust content. In general, soil reinforcement using 15% aggregate dust content is a cost-effective and optimum improvement solution for expansive subgrade soil which meets the sub-grade requirements and specifications.