Improving Engineering Properties of Expansive Soils of Addis Ababa by Blending with Pozzolanic Sand Found around Meki Town
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Date
2020-12
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Addis Ababa University
Abstract
Black Cotton Soils exhibit high swelling and shrinking when exposed to changes in
moisture content and are most troublesome soils leading to failure of civil engineering
structures constructed on such soils. The purpose of this study is to investigate the effect
of pozzolanic sand on improving the engineering properties of expansive soil collected
from Addis Ababa around Koyefeche condominium site.
In this research, pozzolanic sand found around Meki Town was used to treat problematic
expansive soil. The pozzolanic sand used for treating the expansive soil was pulverized to
pass certain sieve sizes. In this particular research, to consider the size effect of pozzolanic
sand on treating the expansive soil, pozzolanic sand passing 150μm and 75μm sieve size
were used to treat the expansive soil. The pozzolanic sand crushed to a size less than
150μm was blended to the soil up to 25% at 5% percentage increments whereas the
pozzolanic sand crushed to a size less than 75μm was blended with soil to a maximum of
15% at 2.5% percentage increments by dry weight of the soil.
Soil treated with the pozzolanic sand showed improvements to plasticity, strength and
swelling. As soil is treated with pozzolanic sand the plasticity of the soil decreased, the
dry density of the soil increased, the optimum moisture content decreased and the swelling
pressure also decreased. Besides, the compressive strength of the soil increased as the
percentage of pozzolanic sand is increasing. For the sizes of pozzolanic sand considered
the pozzolanic sand crushed to a size less than 75μm improved the engineering properties
of expansive soil than the pozzolanic sand crushed to a size less than 150μm when blended
with the expansive soil.
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Keywords
Expansive Soil, Pozzolanic Sand, Soil Improvement, Atterberg Limit, Compaction, Swelling Pressure, UCS, Free Swell Value