Browsing by Author "Merga, Soressa"

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    Effect Of Sample Height on Stress- Strain Behaviour of Undrained Shear Strength of Addis Ababa Red Clay Soil Using Ucs Test
    (Addis Ababa University, 2016-10) Merga, Soressa; Tadesse, Samuel (PhD)
    In this work, the effect of sample height (H/D) on the stress-strain behavior of undrained shear strength of red clay soil in Addis Ababa from a depth of 1.5m and 3m below the ground surface using unconfined compression test was assessed. In most scientific and technical standards, (H/D) of between 2 and 3 is generally accepted. This acceptance is based on the smooth slope of the change in shear strength of the soil at various (H/D) ratios and considering plate effect. But, there was no discussion about the failure pattern developed within the selected specimens size was full fill the assumptions made about stress-strain properties of soils. Therefore, this thesis investigated the effect of the specimen’s size on the stress-strain behavior and undrained shear strength of red clay soil in Addis Ababa by testing undisturbed and compacted cylindrical specimens at different moisture content with four various H/D ratios ( i.e. 1, 1.5, 2, and 2.5), while the specimens’ diameter was constantly used as 38mm. The test results indicated that the length of stress-strain curve increases with decreasing specimen’s height. The specimens with H/D = 1 attained its peak strength at large axial strains and strain at failure is too small as specimen’s H/D increased to 2 and 2.5. But, the range is not too much in both undisturbed and remoulded samples. The unconfined compressive strength and undrained shear strength of the sample also decreases with increasing H/D ratios. In addition, the failure pattern develops(ed) with the various specimens height changes from non-uniform to uniform as H/D ratio of the specimens decreases. For the H/D = 1, the shear failure plane and deformation are uniformly distributed with in the entire of specimens height and as the specimens H/D ratio increases, the deformation and shear failure distribution are localized to some portions of the specimens height. This indicates as sample height is one of the factor which causes non-uniform stress-strain distribution with in clay soils. Generally, based on the uniformity of the failure mechanism developed with in the specimens height and the assumption made during calculation of axial strain, the specimens with H/D = 1 is preferable and based on axial strain ranges at which the sample attain its peak strength, sample with H/D = 1 to H/D = 2 is preferable. Accordingly for red clay soil sample in Addis Ababa it is possible to use sample with H/D = 1 to H/D = 2and further study was needed on the effect of end platen to highly recommend.