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Many of the soils of Ethiopia are covered by expansive soil, and are difficult to use in the
construction of highways and airfields because of their high content of plastic clay and their
expansive tendencies. The existence of expansive soil in Jimma area has caused damage to the
light building, asphalt pavement, and buried utility lines. Several methods have been developed
successfully to use pozzolanic materials such as Portland cement, lime, fly-ash, bitumen, and
polymers for high strength concrete, soil improvement, and other civil engineering works. The
over-dependence on the utilization of industrially manufactured soil-improving additives cement
and lime has kept the cost of soil stabilization very high. These studies mainly focused on
determining the effect of the mixture of corncob ash with lime on the Engineering properties of
black cotton(BC) soil. Due to different soil problems, searching for the best soil stabilizer to
overcome problems that occur by the BC soils is still being the main concern to achieve the
required soil engineering properties. In order to address the aforementioned purposes, two
subgrade soils were collected from Jimma City around Mendera Kochi( Green Sefer) and
Merkato Sefer around the Police station. The soil samples collected from a local area within a
depth of 1.5-2m. The laboratory tests which were carried out Moisture content, Specific Gravity,
Grain size Analysis, Liquid limit test, plastic limit, plasticity index, permeability, UCS, CBR,
swelling index, compaction, XRF and XRD. The samples tested on black cotton clay, black cotton
clay+ % corncob ash, Black cotton clay + % corncob ash + % lime using different apparatus as
per the procedures laid down in American standard of testing materials and Ethiopian road
authority manuals. The data processing and analyzing techniques used were both descriptive and
analytical methods. The test results indicated that the Natural sub-grade soils are A-7-5 as per
the AASHTO soil classification system and CH as per USCS. As far as the engineering properties
of natural subgrade soils were studied, the two soils were highly Swelling clay soils. The two soils
have almost similar Engineering properties. Sample-1 has PI of 66.28 %, FSI of 100%, CBR of
1.24%, MDD of 1.54% and OMC of 24.5%. Likewise, Sample-2 also has PI of 66.58 %, FSI 87%,
CBR of 1.54%, MDD of 1.57%, and OMC of 24%, and both samples Categorize as Illite, and
smecitite minerollogically. As the amount of Lime ratio increases LL, PI, OMC, FSI, CBR swell
decreased whereas PL, MDD, CBR are increased, rather than Corncob ash alone. But the
amount of Lime decreasing with increasing CCA ash beyond 2% the results were decreased as
the respective test. For this study, 2% CCA + 6% LIME was found out to be the optimum ratio
which achieved by most of the geotechnical parameters in the study. The XRD results indicated a
general reduction in peak intensities in all clay minerals that are present in the soil and, most
significantly, in montmorillonite. Finally, Microscopic Analysis using SEM & EDX should be
taken to show the presence of C-S-H & C-S-A-H in both CCA and Lime treated clay soils. |
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