Engineering Geological characterization and suitability analysis of a subgrade soil – A case study on selected section of Ambo – Wolisso Road project, South western Ethiopia
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Date
2017-05
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Addis Ababa Universty
Abstract
The performance of a pavement is highly controlled by the underlying roadbed
soil geotechnical characteristics. A subgrade provides support for upper layers of
a pavement structure that are constructed upon it and the traffic load. The
purpose of geotechnical characterization of a subgrade is to evaluate the quality of
the subgrade based on various results of insitu and laboratory test and sound
geotechnical principles that would impact the pavement performance.
In the present study the subgrade soils are characterized on selected section of
Ambo-Wolliso road located in south western Ethiopia, Oromia region. The
geographic location of the study area is bounded by UTM coordinate of 80 56’ N
370 52’ E and 8049’ N 37053’ E. the objective of the study were 1, to characterize
the subgrade material based on the engineering geological parameters 2, to assess
the suitability and bearing capacity of the subgrade soil 3, to suggest some
counter measures for the unsuitable part of the subgrade soil.
To achieve this objective, a total of 16 subgrade soil samples have been taken at
1km regular interval and tests were conducted at project geotechnical laboratory
for the determination of Atterberg limit, specific gravity, Natural moisture
content, grading, Maximum dry density and Optimum moisture content,
California bearing capacity and swell value and hydrometer test is conducted at
Addis Ababa university Engineering Geological laboratory.
Finally, interpretation have been made with the data obtained from field works
and laboratory investigation, supported by previous studies, research and
standard manual of the subgrade characteristics. From the laboratory
investigation it has been concluded that about 37.5 % of the subgrade soil is found
to be unsuitable on the bases of bearing capacity. Hence, remedial measures such
as removal and replacement, proper drainage design and blending with locally
available materials are proposed.
Key words: Subgrade soil, Suitability Analysis, Expansive soil, Volcanic ash
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Keywords
Subgrade soil, Suitability Analysis, Expansive soil, Volcanic ash