Abstract:
Infrastructure development is one of the key player and backbone to sustain economic activities
of every country. The stability of the infrastructures depends totally on the stability of the soil
at which it rests. Our country Ethiopia consist of various types of soils in different areas as
sandy, clayey, silts, granular soil, black cotton soil etc. Some of these type of soil are having
poor bearing capacity which are not suitable to bear the structural load of road and have a
significant influence on planning, design, construction, and maintenance. In order to improve
these deficiencies, stabilization was used to enhance the bearing capacity of mentioned soil.
This research focused on evaluating the effect of lime and lime-coffee husk ash used as a
stabilizer on the expansive soil in Jimma city, JiT Campus. The sample used for this study was
selected purposively composed of the expected sample size. This study majorly aimed at
reducing the cost of soil stabilization in that the usage by considering the lime as control at
constant percentage and CHA as cheaper alternative stabilizing agent by assessing the
properties of soil free of agent and a mixture of soil and Lime, soil and Lime-CHA of varying
amounts. The tests carried out on the properties of both natural and stabilized sample include;
Atterberg limits, Specific gravity, Compaction, free swell index, linear shrinkage and CBR.
Hence, experimental investigations have been made on natural soil and the sample was
expansive in nature and classified as a heavy clay with 48% PI and 2.10% CBR value.
Additionally, the study was continued using lime and coffee husk ash to improve properties of
expansive soil. Initially, the sample was stabilized with lime at (4%, 6%, 8% & 10%). The
results indicates that increasing the blending ratio of lime content reduced the PI of the soil
up to 6% and started to increases and CBR value increased up to 6% and decreased at higher
percentages. Moreover, the MDD value decreased while OMC increased similar to the other
properties up to 6% and reversed as the content increased. Therefore, based on the test results,
the optimum percentage of lime was investigated at 6% and the researcher used 5% of lime as
a control even though the result was within the range of ERA requirement for subgrade soil by
saving 1% for further investigation and blending with coffee husk ash at various percentages.
Thus, 5%L and varies percentage of CHA mixes (i.e. 5%, 10%, 15%, 20%, and 25%), were
investigated and, it improves all the properties at 5%+20% CHA, which fulfilled the ERA
subgrade soil requirements. Therefore, it was recommended by the researcher to use 5% Lime
+ 20% CHA as the percentage of stabilizing agent for the subgrade soil.
