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Effect of Subsequent Drying and Wetting on Small Strain Shear Modulus of Unsaturated Silty Soils Using Bender Element

Hashemi, Amir Hossein | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50033 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khosravi, Ali
  7. Abstract:
  8. Evaluation of the seismic-induced settlement of an unsaturated soil layer depends on several variables, among which the small strain shear modulus, Gmax, and soil’s state of stress have been demonstrated to be of particular significance. Recent interpretation of trends in Gmax revealed considerable effects of the degree of saturation and hydraulic hysteresis on the shear stiffness of soils in unsaturated states. Accordingly, the soil layer is expected to experience different settlement behaviors depending on the soil saturation and seasonal weathering conditions. In this study, a semi-empirical formulation was adapted to extend an existing Gmax model to infer hysteretic effects along different paths of the SWRC including scanning curves. In the proposed model, effective degree of saturation and confining pressure are used as two key variables to determine Gmax. Also, the model takes the effect of plastic loading into account by consideing plastic deformation of the specimens. The suitability of the proposed approach is validated against experimental results from a series of bender element tests. In this regard, a bender element system was implemented for the measurement of small strain shear modulus, the axis translation technique was used for suction control, a high pressure hydraulic pump was used to apply high confining pressures to the specimens, and a Digital Image Processing (DIP) method was used to measure volume changes during mechanical loading. Also, a signal processing technique was also modified for the analysis of bender element test results. The tests in these studies were conducted on bonny silt and ardebil silt specimens experiencing hydraulic hysteresis under constant net confining stress conditions. Experimental measurements of the shear modulus at small strain showed a slight hysteresis in the Gmax measurements along the scanning loops of the SWRC, with lower values of Gmax along the wetting curve of the scanning loop. However, results indicated that the value of Gmax was recovered once the main drying path was reached. Results of this study also indicated that Gmax behavior of the silty specimen along the scanning loop is stress dependent. The model was observed to follow the experimental data along different paths of the SWRC including scanning curves
  9. Keywords:
  10. Signal Processing ; Small Strains ; Hydraulic Hystersis ; Soil-Water Retention Curve ; Shear Modulus ; Unsaturated Soil ; Bender Element Test ; Two Dimentional Processing

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