Haile, Mesele (PhD)Wakuma, Fekede2018-06-182023-11-112018-06-182023-11-112007-01http://etd.aau.edu.et/handle/12345678/1240The engineering behavior of soils, wheather formed under temperate or tropical conditions, is determined by certain physical characteristics designated as engineering properties. In practice, since the determination of all the engineering properties of soils is expensive, often index properties, simpler and cheaper engineering characteristics which are indicative are investigated. Residual soil is a soil material derived from the in-situ weathering and decomposition of rock, which has not been transported from its original position. Residual tropical soils can have characteristics that are quit distinctively different from those of transported soils, That is: the conventional concept of soil mechanics is not applicable to many residual soils as it consists of aggregates or crystals of weathered mineral matter that break down and become progressively finer under continuous manipulation. Western part of Ethiopia is characterized by such soils. As mentioned in ERA (Ethiopian Roads Authority) design manual (ERA, 2001) Residual laterites are widely available soil material in these areas. The index properties of such soils have not been studied in detail as per the test recommendations for residual tropical soils. This Thesis is conducted to indicate the index properties of soils of Asossa Town (Capital of Beneshangul Gumuze), which is located in western Ethiopia and covered by residual soils. In this thesis work, the index properties of residual tropical soil have been investigated on the soil specimens taken from Asossa Town by following the test procedures recommended for residual soils. The specimens were tested at different sample preparation conditions prior to conducting the laboratory test and resulted in different end values. The index property investigation in this research includes; Specific Gravity Test, Particle Size Distribution, Atterberg xiii Limit Tests and Free Swell Tests, all tests were conducted at three different test temperatures (at received moisture, air-dried and oven dried at a temperature of 105o c ). Generally it was found that, sample pre-treatment and commonly used soil test procedures for temperate soils when applied to Asossa soils resulted in completely altered test result as compared to the actual test result values obtained by following testing procedures recommended for tropical soils. It was found that there is considerable structural water that could be destroyed by oven drying at a temperature of 105 degrees and must be deducted from every moisture content determinations in Atterberg Limit tests. Sample manipulation is also found to alter the results of the Atterberg Limit values by affecting the bond between soil structures. Therefore, the appropriate test procedures for tropical soils are strongly recommended for research and practical engineering application where such soils are likely to exist.enWestern EthiopiaThesis