UTILIZATION OF WHEAT STRAW FIBER AND CEMENT AS SOIL STABILIZER FOR EXPANSIVE SOIL: - A CASE OF ROBE TOWN

Abstract

A large surface area of Robe town is covered by expansive soils which has a tendency to undergo volume change due to seasonal moisture variation. This study focused on providing an alternative solution for the disposal of agricultural waste wheat straw fiber (WSF) by using it as a reinforcement of expansive soil and again to reduce the amount and cost of cement used for stabilization of expansive soil in case of Robe town. To achieve the objectives of this study, the soils found in Robe town were studied in the field and representative soil samples were collected from different locations at 1.5m and 3m depth below the ground surface. Six undisturbed and six disturbed samples were collected from three test pits for different laboratory tests and each samples were determined according to American Society of Testing Materials (ASTM) and Ethopian Roads Authority (ERA) manual. The laboratory tests which were carried out include Natural Moisture Content, Grain Size Analysis, Atterberg Limit, Specific Gravity, Free Swell, Linear Shrinkage, Compaction, California Bearing Ratio (CBR) and CBR Swell, Unconfined Compression Strength (UCS) and X-Ray Diffraction (XRD). Wheat straw fiber were collected from around study area and choosen for reinforcement and randomly included at different percentage of fiber that is 1%, 2%, 3%, 4%, 4.5% and 5% with length of 1.5cm by weight of raw soil and different percentage of cement studied by different researchers including 8%, 7%, 6%, 4%, 3% was used to control the swell and shrink behavior of expansive soil. According to Unified Soil Classification System (USCS) and American Association of State Highway and Transportation Officials (AASHTO) the test results indicate that natural soils collected from study area were categorized as fair to poor performing soil groups interms of as a subgrade material. In addition, the soil stabilization was done after knowing the type and property of the soil. Relative to the natural soil the maximum dry density and strength of the stabilized soil was increased in the presence of wheat straw fiber and cement. But as amount of cement decreasing while increasing wheat straw fiber beyond 4% the improvement was lower. And also before utilization of wheat straw fiber as reinforcement of soil different pretreatment including 3% of sodium hydroxide (NaOH) and Hot Water(30min) was used to improve the bonding quality, to improve degradation property with time and extraction of certain amount of chemical constituents. For this study (3%WSF + 7Cement) was an optimum ratio by considering safety in addition to economy and which achieves by improving most of the geotechnical properties of soils of Robe town