Investigation of Influence of Compaction onThe Stabilityof Earthfill Dams of Tropical Soils
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Date
2003-11
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Addis Ababa University
Abstract
Dam construction is one of the major civil engineering activities, which enhance
development. If the construction of such infrastructures can be achieved within sound
technical and affordable financial capacity, then it is possible to realize the dream for
development and well-to-do life.
One of the merits of earth fill dams is that they can be constructed from locally available
natural material (soil) within sound technical and affordable financial capacity. For soils of
a given locality to be used safely and economically, appropriate methods of determining
the geotechnical properties and shear strength parameters have to be investigated and
developed. In addition to this, the appropriate methods of compacting locally available
tropical soils have to be developed.
Accordingly, in this paper the influence of compaction on the stability of small earth fill
dams of local tropical soils has been investigated. In addition to this, some peculiar
geotechnical and geo-chemical characteristics of local tropical soils that have been used in
construction of earth fill dams have been studied. Accordingly, the fill material of the
cofferdam of Gilgel Gibe Hydroelectric Project has been obtained to be true laterite, while
the core material of Dire Dam and the red clay soil of Addis Ababa (Semen Gebeya Area)
have been obtained to be lateritic.
The soil samples were compacted at optimum moisture content, at drier of the optimum
moisture content and at wetter of the optimum moisture contents. Then, triaxial tests were
done on the soil samples to investigate the variation in shear strength properties of these
soils, which ultimately affect the stability of the earth fill dams. Compaction moisture has
been obtained to influence the stability of earth fill dams. Samples compacted on the drier
side of optimum moistures registered high shear strengths. But these strengths were
observed to be lost upon further increasing the compaction moisture and also upon sample
saturation.
Variation of permeability of compacted soils with respect to compaction moistures and
also the effect of saturation settlements were investigated. Accordingly, Permeability has
been obtained to decrease towards the optimum moisture content. On the drier and wetter
sides of the optimum, higher values of coefficients of permeability have been obtained.
vi The problem of saturation settlement has been observed to occur when the soil is
compacted on the drier side of the optimum moisture.
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Keywords
Tropical ;Soils