Browsing by Author "Habtom, Gebre"

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    Unsaturated Shear Strength Characteristics and Stress Strain Behavior of Expansive Soils of Addis Ababa
    (Addis Ababa University, 2010-11) Habtom, Gebre; Hadush, Seged (PhD)
    Considerable research work has been done on the shear strength properties of most soils. However, very little information is available on the shear strength characteristics of expansive clays. This work studies the shear strength characteristics of an expansive unsaturated soil found in Addis Ababa. Matric suction is one of the stress state variables that control the shear strength of unsaturated soils. Previous studies on the expansive soils are done using the conventional triaxial machine, which is unable to measure matric suction of the soil. The main aim of this study is to determine the unsaturated shear strength properties and the stress strain behavior of expansive soil found in two locations (Bole and CMC) in Addis Ababa. The shear strength behaviour of unsaturated soil is studied in this work using the consolidated undrained modified triaxial compression equipment with measurements of matric suction during the shearing stage. In this work, modified consolidated undrained tests were conducted on 12 undisturbed potentialy expansive soil samples collected from Bole and CMC area at 2.5m depth. Six of the tests were on completely saturated samples and the other six on unsaturated samples. Range of values of shear strength parameters (c, ∅’, and ∅b) were obtained from the consolidated undrained test depending on the applied matric suction. According to the outcome of the research, the deviator stress of soils from Bole area ranges from 90.65 kpa to 130.08 kpa for effective consolidation of 250 kpa for matric suction range of 0 Kpa to 75 Kpa. Similarly the soils from CMC area ranges from 54.03 to 93.41 kpa in deviator stress for effective consolidation of 150 kpa and for matric suction range of 0Kpa to 75 Kpa. The result clearly shows that the shear strength of expansive soils tested for unsaturated case is higher than that of saturated soil and the shear strength increases when matric suction increases.