Basic Engineering Properties of Lateritic Soils Found in Nejo – Mendi Road Construction Area, Welega
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Date
2005-11
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Addis Ababa University
Abstract
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
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Welega