Chemical Stabilization of Expansive Sub-grade Soil Performance Evaluation on Selected Road Section in Northeastern Addis Ababa
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Date
2011-03
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Addis Ababa Universty
Abstract
Expansive soils are characterized by volume change due to variation in moisture content. The
cyclic wetting and drying processes causes vertical movements in expansive soils and these
movements lead to failure of pavements. These soils have very low load bearing capacity too
when wet. These problematic expansive soils, therefore, when encountered as sub-grade
should be avoided or treated properly. The removal of expansive soils and replacement with
suitable fill material is an appropriate method in areas like Addis Ababa in most cases where
there is suitable fill material available nearby. At places, however, its feasibility depends on
the availability of suitable fill material within economic distances and the thickness of the
poor sub-grade soil to be replaced. Chemical stabilization is another alternative being applied
worldwide even if the method is at a conceiving stage in Ethiopia. In recent years there are
tendencies to use lime and other chemicals to stabilize sub-grade and sub base materials by
Ethiopian Road Authority (ERA) and Addis Ababa City Roads Authority (AACRA). In the
present study, hence, the performance of a locally manufactured hydrated lime and an
imported industry product Anyway Natural Soil Stabilizer (ANSS) were evaluated based on
laboratory test results on expansive sub-grade soils collected from Gerji area. The sub-grade
soil was first characterized based on Atterberg limits, linear shrinkage, CBR and percent
swell of CBR. The test results showed that the sub-grade soil is classified as A-7-5 in the
AASHTO and MH in USCS systems. These soils have very low load bearing capacity and
are highly expansive nevertheless of the mineralogy of the sub-grade soil samples have no
montimorillonite, as expected in such soils. Two soil layers on colour variations were
observed in the field: the upper dark gray clay soil and the lower light gray clay soil. The
effects of the chemicals were then evaluated on two soil samples. The improvement of the
sub-grade soil samples increased with increasing both dosages as well as curing periods. In
general terms, increasing the dosage has more significant effect than that of increasing the
curing period and 4% of either chemical has resulted in adequate improvements of the subgrade
soil. In most cases the performance of hydrated lime is better than that of ANSS and
the improvement of the dark gray clay soil is better than the light gray clay soil.
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Keywords
Expansive Soils