Evaluation Of Improvement Techniques For Strip Foundation On Expansive Clay Soils In Gezira
Evaluation Of Improvement Techniques For Strip Foundation On Expansive Clay Soils In Gezira
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Date
2015-05-14
Authors
Saeed, Ibrahim Mohammed Ahmed
Journal Title
Journal ISSN
Volume Title
Publisher
UOFK
Abstract
Most buildings and irrigation structures founded on Gezira soil, especially
in agricultural areas e.g., Gezira Scheme, were subjected to damages due to
up-heave forces caused by expansive soils. The owners of these buildings
have paid much money in repairing and rebuilding these structures.
The first aim of this study is to identify and classify the Gezira soil in order
to facilitate studies and researches on it. The second aim is to evaluate the
effect of some intercepting medias used between the expansive soil and
brick strip foundation, through laboratory and field tests, to reach the
adequate one to be used in Gezira soil.
Disturbed and undisturbed soil samples were collected from depths up to 6
m at 13 locations in Gezira Scheme area, selected to represent the whole
Gezira area. The samples were tested in the laboratories of the BRRI,
University of Khartoum. The results showed that the soils of the whole
investigated area, especially that taken from the upper 3 m, are clay of high
plasticity and highly expansive. The results also showed that the clay depth
in Gezira decreases from south to north and from near the Blue Nile to far
from it. This supports the theory of Tothill (1946,1948) and Jewitt (1955),
that the clay of Gezira was transported by the Blue Nile from Ethiopian
high lands.
To study and evaluate the effect of intercepting medias on expansive soil,
some medias were tested in the laboratory by putting them between the
compacted expansive soil, brought from Barakat, the headquarter of Gezira
Scheme, and weights which simulate the weights of brick strip foundations
on site. The used medias were cohesive non-expansive soil (CNS) of 2.5,
5.0, and 7.5 cm thickness, sand, expansive soil stabilized with 6% hydrated
lime, gravel, and 10 mm steel plate with 20% perforations. The result of
this test showed that the CNS was the best among the tested medias in
resisting the vertical heave of the soil and the thickness has an important
role.
A field test was carried out at Barakat, where the soil samples were taken
for the laboratory test, to study on site, the effect of the intercepting medias
used in the laboratory test. Typical brick walls were built in the test area
with the intercepting medias between them and the expansive soil. Two
cycles of wetting and drying were carried out for a total period of 537 days.
The results also showed that the CNS was the best in resisting vertical
heave through the first two months of the first cycle but it lost this position
in the second cycle.
Another laboratory test was carried out to compare the developed swelling
pressure between the CNS and sand of different thicknesses. The results
showed that when the thickness of intercepting layer was small, less than
half of expansive soil thickness, the sand was better in resisting the
swelling pressure than the CNS and vice versa.
From the above, it is clear that the CNS is effective in resisting the heave
and swelling pressure of expansive soil but more investigations are
required to insure the durability of this option.
Description
238 page
Keywords
Improvement Techniques,Strip Foundation,Expansive Clay Soils,Gezira