Investigation on the Engineering Properties of Soils in Bedelle Town

Abstract

Investigation of the ground conditions is used for the safe and economical design of the sub structure. It is also necessary to obtain sufficient information on type, characteristics and distributions of a soil and rock underlying a site for proposed structures. Therefore, in a country like Ethiopia which is under a higher rate of economic development, geotechnical investigation of engineering properties of soil is essential as it fosters availability of ready-made data for planning and design of engineering structures such as building foundations, pavements and retaining structures. Investigating the engineering properties of typical soil in Bedele town is the objective of this research. To achieve these objective six representative disturbed and undisturbed samples at average depths of around 1.5 m and 3 m were collected and engineering properties of soil such as grain size distributions, Atterberg limits, free swell, compaction, and unconfined compression parameters have been studied. Accordingly, Laboratory tests carried out revealed the following ranges: the natural moisture content 27-47%, specific gravity of the soils 2.45-2.75, free swell index 25- 50%, liquid limits 52-74%, plastic limit 30-52% and plasticity index 12-36%. The results of grain size analysis showed that clay content ranging from 46 -80%, silt content from 19-46%, sand from 1.3 -16.7% and gravel from 0-83%. The unconfined compressive strength of the soils in the study area ranges from 225 -333kN/m2 and undrained shear strength; from 112.5 – 166.5 kN/m2 . Based on the above data, implementation of commonly used AASHTO and USCS standard soil classification techniques demonstrated that, AASHTO classification shows that soils of the study area are A-7-5 which means clay soil with poor quality as a subgrade material. USCS indicates two main types of soils, which are: CH, high plastic clay soils, and MH, high plastic silt soils. Since pit excavation method of exploration is used, the outcomes would be applicable only for light structures which under lie their foundation up to depth of 3m.