Investigation in to Shear Strength Characteristics of Expansive Soil of Ethiopia
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Date
2004-11
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Addis Ababa University
Abstract
Considerable research work has been done on the shear strength properties of most soils.
However, very little information is available on the shear strength characteristics of
expansive clays. This is mainly due to the fact that many investigators have concentrated
most of their efforts towards finding solutions to the swelling behavior associated with
these clays. However, the strength behavior of expansive clays need not be overlooked.
Factors such as swelling and shrinkage, for example, influence the soil strength
significantly and their effects are difficult to account for in most laboratory shear tests.
Furthermore a thorough knowledge of shear strength is required to estimate the bearing
capacity of expansive clay soils and also to evaluate the stability of dams, road and
railway embankments built in these soils areas.
Therefore, in this paper, Unconsolidated Undrained triaxial shear strength tests were
performed on unsaturated soil and on some saturated soil samples collected from
different locations of Addis Ababa, unsaturated soil sample of Gambela and unsaturated
soil sample of five major roads (i.e. Addis-Modjo, Addis-Ambo, Addis-Debreberhane,
Addis-Weliso and Addis-Ghoastion roads). The purpose of the study was to know the
shear strength properties of expansive soil. Range of values of shear strength parameters
(cohesion and angle of internal friction) were obtained based on unsaturated soil samples.
According to the outcome of the research, the shear strength of expansive soil ranges
from 30-150Kpa in cohesion and 3-25 degree in angle of internal friction in UU test on
unsaturated soil. For saturated soil sample in UU test the cohesion ranges from 55-
94Kpa. There is a decrease in strength in the saturated samples, which shows that the
degree of saturation and the suction pressure can have major influence on the shear
strength of expansive soil.
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Geo-Technical Engineering