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Dynamic Parameters of Saturated and Unsaturated Sand at Different Range of Shear Strain Levels in Cyclic Simple Shear Test

Golshan, Zeinab | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40642 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. In this investigation, a series of cyclic simple shear tests were carried out in order to evaluate dynamic parameters of Babolsar and Toyoura sand at levels of saturation 25, 50, 75 and 100%. 96 tests were conducted using SGI type cyclic simple shear device. The specimens were cylindrical, with 7cm diameter and 2.2 cm height. The tests were performed under both drained condition (constant-load) at levels of saturation 25, 50%, and undrained condition at levels of saturation 75, 100%. All tests were performed under vertical consolidation stress of 50 and 150 kPa, relative density of 30 and 70% and cyclic shear strain of 0.5, 5 and 10%. The tests were shear strain-controlled with an approximately sinusoidal shape of cyclic loading. The loading frequency was 0.5 Hz, and the tests were carried up to 200 cycles. The shear modulus approximately remains constant under cyclic shear strain of 5 and 10% by change of degree of saturation from 25 to 50% and increase under cyclic shear strain of 0.5%. Also, in all tests shear modulus increase by change of degree of saturation from 50 to 75%, and these variations are more significant in Toyoura sand compared to Babolsar sand. The shear modulus decrease when degree of saturation reaches to 100%. For the shear strain of 0.5%, by change of degree of saturation from 75 to 100%, shear modulus decrease less than shear modulus corresponding to the shear strains of 5 and 10%. This is due to samples liquefaction in higher cyclic loadings. It is to be noted that the decrease of shear modulus is greater for looser samples. Damping ratio approximately is constant over the range of saturation degree from 25 to 75% except for those samples with Sr= 75% for which damping ratio decrease under cyclic shear strain of 10%. This value increase when degree of saturation reaches to fully saturated state and these variations in cyclic shear strain of 5 and 10% is higher than cyclic shear strain of 0.5%. For unsaturated sands, shear modulus remains constant, and damping ratio decrease by number of loading cycles under shear strain of 0.5%. At degree of saturation 25 and 50%, these values increase and decrease, respectively, and at degree of saturation 75% both of them decrease under cyclic shear strain of 5 and 10%. In saturated sands, the increase of loading cycles leads to liquefaction under undrained condition, and shear modulus and damping ratio decrease and increase, respectively. Results indicate that as vertical consolidation stress increase, shear modulus and damping ratio of sand increase and decrease, respectively. Besides, the rate of these variations decrease and increase with the shear strain amplitude, respectively. The shear modulus decrease and damping ratio increase with shear strain amplitude. Furthermore, in most results shear modulus and damping ratio increase and decrease with the relative density, respectively.

  9. Keywords:
  10. Sands ; Shear Modulus ; Damping Factor ; Cyclic Simple Shear ; Saturation Degree

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