Effect of Strain Rate on Undrained Shear Strength and Sensitivity of Red Clay Soil Found in Addis Ababa
No Thumbnail Available
Date
2018-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU
Abstract
Soil presents itself to be one of the most complicated materials owing to widespread variation of its properties
which changes in both geometrical composition and time based contexts. For design and analysis of any
structure supported by soil, the shear strength parameters of the soil are vital and they should be obtained
from laboratory and in-situ tests. Since the shear strength parameters are not intrinsic properties of soil, there
are a number of factors which affect the estimates obtained from tests, out of which rate of loading or shearing
and the initial degree of compaction poses to be the most important factors that should be taken in to account
while conducting the tests.
In Addis Ababa lot of construction activities are seen like foundation structure of heavy duty machineries,
high rise building, slope stability in embankment fill, design of highway pavements and deep vertical excavation.
In doing such activities the strength and properties of soil which the structures to be built must be studied.
The shear strength of the soil is affected by the rate of strain. So it is necessary to incorporate the effect of
varying strain rate on such geotechnical problems. In this study, the effect of strain rate on undrained shear
strength of both undisturbed and remolded samples and sensitivity of red clay soil are investigated using
unconfined compression tests.
In this thesis, the UC tests were carried out on undisturbed and remolded samples using different strain
rates which are obtained from the coefficient of consolidation for each load increment of one-dimensional
consolidation. The strain rates are (0.37, 0.84, 1.03, 1.12, 1.61, 1.75) and (0.23, 0.53, 0.61, 0.68, 1.06, 1.14) for the
undisturbed and remolded samples respectively. The remolded samples are tested for both strain rates in order
to determine sensitivity accordingly.
The undrained shear strength increases from (62.7 to 256.5) kPa and from (59.6 to 157.5) kPa as the strain
rate increases from (0.37 to 1.75) mm/min for undisturbed and remolded samples respectively and also from
(45.3 to 123.9) kPa as the strain rate increases from (0.23 to 1.14) mm/min for the remolded samples. The
failure strain decreases from (8.95 to 3.29) % and from (15 to 7.24) % as the strain rate increases from (0.37-
1.75) mm/min for undisturbed and remolded samples respectively and also from (15 to 9.21) % as the strain
rate increases from (0.23 to 1.14) mm/min for the remolded samples. The sensitivity increases from (1.05 to
1.63) and (1.38 to 2.07) as the strain rate increases from (0.37 to 1.75) and (0.23 to 1.14) respectively.
The test results show that, as the strain rate increases the undrained shear strength increases and the
failure strain slightly decreases for both undisturbed and remolded samples and also the sensitivity increases.
Besides on the basis of their sensitivity, the soil in the study area can be classified as insensitive.
Description
Keywords
Strain rate, Undrained shear strength, sensitivity, red clay soil