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Assessment of the Hydro-Mechanical and Shear Behavior of Collapsible Soils by Using Suction- Controlled Triaxial Apparatus- A Case Study: Loess of Gorgan

Ghazi Zadeh, Shahin | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45603 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. In geotechnical engineering, collapsible soils as a part of problematic soils has an extreme importance since as a mutual effects of applying load and increasing their water content, Soil’s inter-particle forces become weak, and therefore, the soil experiences sudden large volumetric change known as collapse. Foundations built on these soils might experience sudden, large settlement. Collapsible soils exist in almost all continents, and many damages are reported due to the collapse phenomenon of these soils.
    Due to the importance of this issue, and lack of comprehensive studies related to the volumetric and shear behavior of these soils, in this study, triaxial wetting test are performed in conditions of constant mean net stress and decreasing suction to study Hydraulic and Mechanical behavior of Collapsible soils. Also, triaxial shear tests in conditions of constant amounts of mean net stress and matric suction are performed to investigate the shear behavior of collapsible soils. Both series of tests are performed on reconstituted specimens of loessial soils of Gorgan, in north of Iran, which is believed to have moderate- high collapse potential. Tests are performed with a suction controlled triaxial apparatus which is able to accurately monitor the amount of specimen volume change and its water content during tests. Results show the stepwise volumetric changes of specimen, or collapse, during both wetting and shear tests, and the specimen collapse during the test depends to amounts of mean net stress and matric suction.
    Another goal of this study is comparing the hydro-mechanical and shear behavior of reconstituted samples of this study with the behavior of undisturbed samples from previous studies as an unsaturated soil. An investigation which is barely performed in literature in the area of Unsaturated Soil Mechanics. Both Undisturbed and Reconstituted specimens have the same initial conditions, and they are tested in the same stress path with the same apparatus. The results of this investigation show the considerable differences in hydro-mechanical and shear behavior of reconstituted and undisturbed samples due to differences in soil fabric. For example, the amount of water absorbed by specimen, volumetric collapse, and critical state line differs for undisturbed and reconstituted specimens.
  9. Keywords:
  10. Loess Soil ; Unsaturated Triaxial Device ; Collapse Analysis ; Unsaturated Soil ; Soil Mechanics ; Triaxial Weting Test

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