Haile, Messele(PhD)Dibisa, Jiregna2018-06-192023-11-112018-06-192023-11-112008-03http://etd.aau.edu.et/handle/12345678/1497The classification properties and composition of lateritic soils, developed on Tertiary basalt, granite and metamorphic rocks like gneiss and Shists in Nedjo, Mendi and Assosa areas have been investigated. X-ray diffraction analyses showed that the soil comprised minerals of Kaolinite and Smectite group such as Kaolinite, Quartz, Dickite, Nacrite, Muscovite, Vermiculite, Geigerite, Zektzerite, Tridymite and Gibbsite. Chemical analyses showed there was a concentration of sesquioxide minerals but no amorphous material present in the soil. Comparison between moisture content at air-dry temperature (50oC with 30% relative humidity) and that of oven drying at 105oC indicates that there is no structural water. For the lateritic soil of Nedjo, Mendi and Assosa, unlike the oxidation of the free secondary clay minerals, the fact that there is no pronounced structural water found and/or amorphous clay minerals showed that, dehydration does not significantly affect the index and/or engineering properties of lateritic soils of this area. In all the cases there is no significant difference observed between the Atterberg limits obtained from test on a specimen mixed for 5min and that of 25min, this indicates that the cementation of the clay particles is too high to be disaggregated with in 25min further mixing and can also be related to the degree of laterization. Analysis of specific gravity of the soils shows that, increase in temperature from its in situ condition to an air-dried equivalent of 50oC oven temperature reduces specific gravity by an average of 4%. viii Analyses of the grain size distribution and other physical properties indicated that the soil was not homogeneous within the laterite zone. Atterberg Limit test results for the soil falls below the Casagrande A-line. There were significant differences between the values of plasticity index determined for as received condition compared with air dried samples. High values for both the liquid and plastic limits may be due to the water retention capacity of porous microaggregations in the soil. This can be correlated with the degree of laterisation, which depends on the ambient climate, topography and vegetation of the area.enNedjo;Mendi ;AssosaThesis