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.
