Abstract:
Most Civil engineering structures is to be founded on soil. The soil on which the structure is
to be built should be capable of withstanding the load to be imposed on it. However,
naturally there exist problematic soils to be used as foundations or construction materials.
Expansive soils present significant geotechnical and structural engineering challenges over
all the world, with costs associated with expansive behavior estimated several billion
annually. In Ethiopia, nearly 40% surface area of the country covered with expansive soils.
The objective of this thesis is to investigate experimental road subgrade soil properties of
Diri – Masha Road Project (Gimbo – Konda) and mitigation measure taken by partial
replacement method for expansive soil. There are two main types of soil samples for this
study: experimental road subgrade and suitable borrow material. Sampling method for
experimental subgrade soil is dig or excavates by digging tools with labor to one point five meter depth at three km interval & recovers the bore holes / trial pits after samples collected.
For this study twenty experimental subgrade soils and two suitable borrow materials
collected at near section of the road project to use for treatment of experimental expansive
subgrade soil.
This research data was collected and organized both in numerical form and in words. After
sorting out the effective data, the numerical portion of the data was analyzed using excel
software, charts, tables& figures. From total twenty experimental subgrade soils tested by
ASTM test method, only eight is expansive soil and need treatment. Test result of expansive
soil are, LL: 61-76%, PI: 30-42%, CBR: 4.8-7%, Swell: 2.4-3.7%, free swell: 55-107.33%
and Classification of soil: MH-CH. The optimum ratio for the expansive soils is 40% using
both borrow materia1s. The analysis has been tried on four expansive experimental subgrade
soils and two suitable borrow materials & taken as representative experiment for the
remaining. The maximum improvements on engineering properties were observed on LL, PI,
free swell and CBR. & minimum on Specific gravity. From this study, the thesis document
can be used as a reference for geotechnical engineering investigation, higher institution,
stack holders like contactors, consultant and ERA can use it when required
