REINFORCEMENT OF PROBLEMATIC SUB-GRADE SOIL USING ENSET FIBER WITH CEMENT: ON DAYE TO NANSABO ROAD SECTION, SOUTH EASTERN ETHIOPIA

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 Daye to Nansabo 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 Enset fiber and cement to be used as a sub-grade road. The experimental programs were carried out for natural soil alone, soil-Enset fiber, and optimum soil-Enset fiber with cement 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. The percentage of Enset fiber by mass of dry soil was 0.5%, 1.0%, and 1.5%, and cement content of 2%, 4%, and 6% was taken. Using 0.5% to 1.5% Enset fiber on three test pits, the OMC increased from 25.2% to 27.2%, 25.15% to 26.8%, and 25.5% to 27.3%, respectively, while the MDD decreased from 1.475g/cc to 1.455g/cc, 1.47g/cc to 1.45g/cc, and 1.48g/cc to 1.46g/cc. The CBR value increased to 1% of fiber content and then decreased. From the result, 1.0% of Enset fiber was taken as the optimum percentage for the soil-Enset fiber mix. The MDD and CBR values increased and OMC decreased with the addition of cement content from 2% up to 6% on optimum Enset fiber. The maximum CBR values from three pits, 7.03%, 7.14%, and 7.25% were obtained at 1% Enset fiber and 6% cement content. The plasticity index of the soil-cement treated sample at 6% of cement content after the curing periods of the first 21days was 9.12%, 7.14%, and 5.43%, were obtained. The Enset fiber coating with kerosene leads to a reduction of water absorption capacity by 32%. The cost comparison demonstrates that using Enset fiber and cement for improvement saves 19.3% over replacing it with suitable material. In general, soil reinforcement using 1.0% Enset fiber mixed with 4% -6% cement content is a cost-effective and optimum improvement solution for expansive subgrade soil which meets the sub-grade requirements and specifications