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Effect of Principal Stresses Direction, Anisotropic Consolidation and Silt Content on the Behavior of Silty Sands by using Hollow Cylinder Apparatus

Keyhani, Reza | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 45201 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. In this research, the effect of various parameters on the behavior of silty sands is evaluated under special loading conditions. To evaluate these parameters, the hollow cylinder apparatus of the Advanced soil mechanics at Sharif University is used. In this research the effect of principal stress directions, initial anisotropic consolidation, silt content, effective mean normal consolidation stress and intermediate principal stress are studied on the behavior of silty sands including the strength and pore water pressure. In order to evaluate these parameters, the specimens are made with wet tamping method with 0, 10, 20, 30 and 40 percent of silt. Before applying shear load to specimen, the test specimens were saturated by flushing deaired water from the base of the specimens and simultaneously a back pressure is applied. The effective mean normal consolidation stress is selected to be 100, 200 and 400 kPa and the specimens are consolidated with and stress ratio Kc ( ) 0.33, 0.5 and 1. After consolidation stage is completed, the specimens are loaded with principal stress directions (α) of 20, 40, 60 and 80 degrees and intermediate stress parameter of 0.2, 0.5 and 0.8.
    In this research, more than 150 hollow cylinder specimens are tested. The results show that tendency to softening increases by increasing α for sand and silty sand specimens with low and high relative densities. For a selected α, changing Kc doesn't influence the behavior of sandy specimen with low relative density and the tendency to softening behavior decreases by increasing Kc. However for sandy specimen with high relative density, increasing Kc changes the behavior from no excess pore water generation to phase transformation. Generally for all of values selected for α, b and P'c, adding silt up to 30% by weight to the sand host reduces the shear strength of the material and then by increasing silt content to 40%, the shear strength of the material increases. However it is still smaller than the shear strength of pure sand specimen. Therefore shear strength decreases by increasing silt content up to a threshold value and then it increases by adding more silt content. Also the minimum shear strength decreases by increasing Kc for sandy and silty sand specimens regardless of the amount of α, b, P'c and relative density.
  9. Keywords:
  10. Intermediate Principal Stress ; Principal Stress Axis Rotation ; Hollow Cylinder Apparatus (HCA) ; Silty Sand ; Anisotropic Consolidation ; Excess Pore Water Pressure ; Mean Principal Stresses

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