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The Effect of Induced Anisotropy on the Dynamic Properties of Unsaturated Sand at Constant Suction by Hollow Cylinder Apparatus

Adineh, Kianoush | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53137 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Soils have an anisotropic response, and mechanical and dynamic properties of this material are greatly dependent on the direction and magnitude of principal stresses. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to perform tests in similar condition with in-situ. From all the devices used for studying anisotropy of soils, hollow cylinder apparatus is the only apparatus that enables an independent control of both the direction and magnitude of the principal stresses. Moreover, one of the most controversial topics in the unsaturated soil dynamics is determining the shear modulus and damping ratio which are used for assessing many geotechnical problems. Therefore, it is important to study the variation of these two parameters versus the factors affecting them such as shear strain, confining stress, void ratio, and so on.The cyclic hollow cylinder apparatus of Sharif University of Technology has recently been developed for performing unsaturated tests. In this research, the effect of anisotropy on the shear modulus and damping ratio in different shear strains and the shear modulus degradation curve of the Babolsar sand in the initial state conditions of the sample have been studied. The type of anisotropy studied in this research is induced anisotropy investigated through application of cyclic stress under controlled conditions of α (15, 30, 45, 60, 75 degrees) and b (0, 0.25, 0.5, 0.75, 1). Moreover, the effects of confining Stress on soil dynamic properties were investigated through five tests series .The results show that the effect of anisotropy on the shear modulus of sand is very significant. The results indicate that by increasing α to about 45 degrees, the shear modulus rise to a certain value and then decreases with increasing α, and at α=75° it reaches approximately its minimum value. Moreover, the maximum and minimum value of the shear modulus was obtained at α=45° and α=75° (in very few tests at α=15°) respectively. Also, the maximum values for the shear modulus degradation curve and minimum value for the damping ratio were obtained at α=45° and α=75° respectively . In addition, as the confining stress decrease and shear strain increase, the shear modulus decrease and the damping ratio increase. According to the results, the shear modulus and damping ratio did not show a clear trend against the variation in b, and it can be concluded that this parameter has no significant effect on the dynamic properties of soil
  9. Keywords:
  10. Shear Modulus ; Damping Ratio ; Unsaturated Sand ; Hollow Cylinder Apparatus (HCA) ; Principal Stress Axis Rotation ; Intermediate Principal Stress ; Shear Modulus Degradation Curve

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