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Evaluation of the Effect of Anisotropy on Cyclic Behavior of Sands with Hollow Cylinder Apparatus

Zamanian, Mostafa | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46028 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Direction of loading and magnitude of the intermediate principal stress have significant effect on the soil responses. In many of in-situ loading the direction of major principal stress is not coincide to the deposition direction of the soil. Also, the magnitude of the intermediate principal stress should be exerted in the three dimensional loading condition. A reliable assessment of the soil behavior and a good estimation of the soil parameters need to do tests in similar condition with in-situ. So the testing apparatus should be able to control the loading direction in various stress paths. Typical equipments used in the geotechnical laboratory have not the ability to control the magnitude and direction of principal stresses. The cyclic hollow cylinder apparatus can control the magnitude and direction of the principal stresses and imposed minimum non-uniformity on the specimens. The hollow cylinder apparatus used in this study is fully automated and can simultaneously control the five loading axis (i.e. the vertical load, torque, inner cell pressure, outer cell pressure and back pressure). The consolidation control options allow the various anisotropic consolidation statuses. Moreover, the load could be exerted as cyclic or monotonic. The main specifications of the specimens are as follows: 100mm outside diameter, 60mm inner diameter, and 200mm height. In this study the effect of the direction of major principal stress to the vertical (α), intermediate principal stress parameter (b), initial mean normal effective stress (σ'om), the relative density (Dr) and the anisotropic consolidation on monotonic and cyclic behavior of sand has been studied. Babolsar sand (obtained from the South coast of the Caspian Sea) and the Japanese standard fine Toyoura sand were selected as test materials. The majority of samples had tested at 25% and 75% relative density, 50kPa and 150kPa mean normal effective stress, b=0.1, 0.5 & 0.9 and α=10, 30, 45, 60 & 80. Some of samples were tested at different relative densities and confining stresses. More than 350 hollow cylinder tests were done that the results of 130 specimens were reliable. Results showed that in the isotropic loose specimens, the residual excess pore water pressure is affected by intermediate principal stress parameter, while at the dense ones α has the greatest impact. The internal friction angle at steady state was reduced by increases of α. But in dense specimens α had no significant effect on the internal friction angle at steady state. Also, b parameter had no effect on the internal friction angle at steady state. The specimens that tested at α=45 (i.e. b=cte.) or b=0.5 (i.e. α=cte.) showed the minimum cyclic strength. In α=45 loading condition, the shear modulus and damping ratio was minimum and had highest dependency to the b parameter. The response of the anisotropic consolidated specimens (i.e. no shear stress exerted during the anisotropic consolidation) was dependent to the direction of major principal stress during cyclic loading. In this research some empirical and energy based models were used to predict the residual pore water pressure, shear modulus and damping ratio. The modified forms of the models were proposed for the tested materials by regression analysis
  9. Keywords:
  10. Hollow Cylinder Apparatus (HCA) ; Sands ; Intermediate Principal Stress ; Direction Of Major Principal Stress Axis ; Stress Anisotropy

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