Abstract:
Expansive soils are soils that have a property of large volumetric changes, both shrinkage and
swell, due to variations in their moisture content. Their bearing capacity is poor. For road to be
constructed on such soils, the subgrade should be designed to minimize subsequent changes in
moisture content and consequent volume changes thereby improving bearing capacity of the soil.
The subgrade material for road construction within the project of Aseb-Bari lot1 road project,
located in Botar Tolay Wereda, is highly dominated with such types of expansive soils.
An appreciable part of Ethiopia is covered by expansive soil. Most of the roads constructed and
proposed as well as substantial amount of the newly planned railway routes in the country
traverses across expansive soils. The roads on this type of soils fail before their expected design
life, in some cases after few months of completion.
The subgrade material for road construction within Aseb-Bari lot1 road project, located in Botar
Tolay Wereda, is highly dominated with such types of expansive soils. The methods applied to
improve the engineering property of such soil were either to stabilize the existing soil or to replace
the soil with non-expansive impermeable soil to the depth affected by seasonal moisture changes.
In the present research work, the economic advantage of improving the expansive soil with
hydrated lime to that of replacement of expansive soil with material having good strength was
investigated.
For the comparison purpose, first characterization of the native soil and the stabilized subgrade
was carried out. The cost estimated for expansive soil stabilization by hydrated lime within 1km
road was 1,935,618 ETB and the cost estimated for replacement was 2,089,049.60ETB. The
comparison shows that the cost of expansive soil stabilization by hydrated lime was less than the
cost of expansive soil replacement by 7.3%.
This result shows that stabilization of expansive subgrade soil with hydrated lime is more
economical as compared to replacement of expansive subgrade soil for pavement construction.
