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Title: Study of Index Properties and shear Strength Parameters of Laterite soils in Southern Part of Ethiopia the case of Wolayita - Sodo
???metadata.dc.contributor.*???: Mesele Haile (PhD)
Hanna, Tibebu
Issue Date: 3-May-2012
Publisher: AAU
Abstract: Most geotechnical problems such as bearing capacity, lateral earth pressure and slope stability are related to the shear strength of a soil. The shear strength of a soil can be related to the stress state of the soil. The stress state variables generally used for an unsaturated soil are the net normal stress ( –ua) and the matric suction. (Ua- Uw).The index properties of soils are also essential parameters for soil classification as well as for indirect estimation of its potential strength. Because of climatic conditions, ground water tables in tropical and subtropical regions are often depressed. Evapotranspiration often exceeds infiltration. This leads to deep desiccation of the soil profile. Therefore, residual soils frequently exist in an unsaturated state with continuous air in their voids. The pore air pressure will usually equivalent to atmospheric pressure, but the pore water pressure will be sub – atmospheric, i.e. negative due to capillary effects in the small pores of soils. This negative pore water pressure or suction produces an additional component of effective stress, or in other words: the effective stress becomes greater than the total stress. The extended Mohr Circle failure envelope defines the shear strength of unsaturated soil. Identifying the soil characteristic is essential to determine the type of test and test procedure that is applied during sampling, sample preparation and testing. In this thesis, several tests have been conducted to understand the effect of unsaturated soil mechanics on the determination of shear strength parameters and comparison of the result with tests on saturated samples. To this effect the geotechnical and geo-chemical characteristics of soils sampled from Wolayita – Sodo have been investigated. For shear strength parameters determination, undisturbed soil samples were collected and unconsolidated undrained tests and unconfined compression tests were carried out because of the triaxial machine’s limitation to suction measurements. Both saturated and unsaturated tests were conducted to make systematic comparison of the test results. xi Moisture content determination, using oven temperatures of l05°C, 50°C and 35°C were carried out on the soil samples to investigate the variation of structural water. Atterberg Limits were investigated for different testing procedures on the soil samples to evaluate the effect of test manipulation on cement bonds between clay clusters. The liquid limit tests were carried out on soil specimens mixed for 5 minutes and 30 minutes durations. From the test results, the soil under investigation has been affected by manipulation. Specific Gravity Test, Particle Size Distribution, Atterberg Limit Tests and Free Swell Tests were conducted at three different test temperatures (as received moisture, air-dried and oven dried at a temperature of 105°c). These tests were conducted in order to understand the behavior of the soil in the area and classification. According to the result of this research, Moisture content ranges between 26 - 41%, Plasticity Index ranges between 19 – 30%, Clay fraction ranges between 48 - 70, Shrinkage limit ranges11-22, Free swell ranges between 28-38% and Specific Gravity ranges between 2.61- 2.97. The shear strength parameters(C - value) as determined from UU Test ranges between 150-173 Kpa and 12 º -20 º for unsaturated sample respectively. For saturated soil sample, the C- value obtained is 118Kpa and unconfined compression strength (qu) ranges from 215- 385 Kpa. Laterite soils are characterized by high concentration of Iron Oxide, Aluminium Oxide (Sesqueoxide) and Kaolinite minerals. The soils samples subjected to tests fall below A-line under MH (inorganic clay with medium strength) and contain Kaolinite mineral. The activity number which is the ratio of plasticity index to the percent of clay –size friction by weight, is below 0.75, confirming that the soil is inactive.
Appears in Collections:Thesis - Civil Engineering

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