Basic Engineering Properties of Lateritic Soils Found in Nejo – Mendi Road Construction Area, Welega

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Addis Ababa University


Lateritic soils are highly weathered and altered residual soils formed by the in-situ weathering And decomposition of rocks in the tropical and sub-tropical regions with hot, humid climatic Conditions. Their formation also consists of leaching out of free silica and bases and Accumulation of oxides of iron, aluminum or both. This process is called laterization. Laterites Are rich in sesquioxides (iron oxides, aluminum oxides or both) and low silicates but may Contain appreciable amounts of kaolinite. Due to the presence of iron oxides lateritic soils are Red in colour. Laterites are grouped under group of soils with a strong mineralogical influence derived from Clay minerals only found in residual soils. Soil engineering properties under this group are Highly influenced by the presence of sesquioxides. Sesquioxides appear to act as cementing Agents which bind the other mineral constituents into clusters or aggregations. With sufficient Concretion of sesquioxides, the hard concretionary materials are formed. This concretionary Bond is broken down during test manipulation for some lateritic soils. In this thesis work, some peculiar geotechnical and geo-chemical characteristics have been Investigated on soils sampled from Nejo- Mendi road construction area. Accordingly, the soil Samples under investigation have been obtained to be true laterites, in short referred to as Laterites. Moisture content determination using oven temperature of l05°C and oven Temperature of 50°C with maximum relative humidity 30% were also carried out on the soil Samples to investigate presence of loosely bound water of hydration. It was obtained that the Soil samples did not contain loosely bound molecular water in a significant amount. The soil specimens were tested at different sample preparation conditions prior to testing. The Engineering properties investigated in the course of the research work include index tests, Compaction and California Bearing Ration (CBR) tests at oven temperature of l05°C dried, air Dried (oven temperature of 50°C with maximum relative humidity 30%) and as received Conditions on the soil samples. Accordingly, pre-treatment variation has not significantly Change index, compaction and CBR test results. Viii Atterberg limits were investigated for different testing procedures on the soil samples to see Effect of test manipulation on concretionary bond. The liquid limit tests were carried out on Soil specimens mixed for 5 minutes and 30 minutes durations. It was observed from the test Results that the mixing durations has significant effect on the values of liquid limits. Accordingly, the soil samples have been sensitive to te