Stabilization of Expansive Soil Using a Mixture of Saw Dust Ash and Lime in Jimma Town, Ethiopia

Abstract

Expansive soils are always characterized by their high water absorption, high compressibility, high shrinkage on drying and high swelling/expansion on wetting. These expansive soils cause several problems to civil engineering structures. Different methods are often adopted to improve the engineering properties of expansive soils before use for construction purposes. The focus of this study was to evaluate suitability of Sawdust ash(SDA) and lime for stabilization of expansive soils in Jimma town, western Ethiopia. Expansive soil samples were collected from three test pits in Jimma town (Kochi, Shenan Gibe Hospital and Teknicsefer, localities). Various preliminary tests for index properties and strength were determined in the laboratory beside this grain size analysis were done and the test results indicate that the soil samples are expansive soils. leftover of wood processing sawdust (SD) were collected from Jimma town wood processing enterprises and left in an open area for air drying in order to remove its moisture and facilitate easy way of burning. The Sawdust was burnt to ash and the ash was collected and lime is bought from open market. To determine the effect of SDA and lime on engineering properties of expansive soil different laboratory tests were carried out which include: moisture content, Atterberg limits, compaction, specific gravity, grain size,UCS and CBR. Tests were performed on natural and treated soil samples as per the AASHTO and ASTM laboratory test standards. The selected soil samples were characterized and were found A-7-5 category of soil based on the AASHTO soil classification system and CH as per USCS soil classification system which is clay soil of poor engineering properties. The soils were treated with varied proportions of SDA (3%, 5%, 10%, and 15%)and lime (1.5%, 2.5%, 5% and 7.5%)by dry weight of the soil. The results from the analysis show improvement of the geotechnical properties of expansive soil with SDA and lime. The plasticity index and free swelling index, reduced with an increase in CBR and UCS value and better improvement was found when using 5% SDA and 2.5% lime. It can be concluded from the present investigation that expansive soil could properly be stabilized for use as subgrade material. Adequate strength was achieved with 5% SDA and 2.5% lime and which is found to be the optimum SDA and lime contents for improving the engineering properties of the expansive soils.