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Studying the Dynamics Behavior of the Partially Saturated Sand under Different Hydro-mechanical Loading with Resonant Column- torsional Shear and Bender Elements Apparatuses

Toomani, Pooria | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51039 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Khosravi, Ali
  7. Abstract:
  8. Considering the importance of studying dynamic characteristics of soils in the analysis of wave propagation and the design of earth constructions or soil-related structures, as well as the role of Resonant Column-Torsional Shear in determining the dynamic parameters, including shear modulus, damping ratio and wave velocity in soil, this device was designed and developed in this research. The apparatus developed is able to conduct both resonant column and torsional shear tests and also measure dynamic parameters in large ranges of strain. The unsaturated pressure panel built alongside this device and the especial design of the device components have made the above-mentioned experiments feasible on unsaturated soils in a wide range of hydro-mechanical loads. The main reasons and motivation for fabricating this device comprise high importance of RC-TS in determining shear modulus and damping ratio and also the presence of less than five of these devices in our country. Therefore, it provides self-sufficiency for the country in manufacturing this device and also facilitates scientific advances in the field of geotechnical sciences by furnishing universities and research institutes with the accesses to this device. The design and manufacturing process of this device has faced many challenges in order to finally be able to carry out resonant column, free decay method and torsional shear tests in accordance with the standards, and also to measure the values of the two key parameters of the shear modulus and the damping ratio of dry, saturated, and unsaturated soils, under different mechanic and hydraulic loads, at different void ratios, confining stress, water content, grain size, and strains. In order to verify the accuracy of the device and to evaluate the behavior of the shear modulus and damping ratio of unsaturated silty soil under various pressure and strain rates, some experiments were conducted on a number of silt samples with a low plasticity and a void ratio of 0.75 under confining pressures of 100 kPa and 200 kPa. In this study, it is observed that by increasing the strain rate applied in the dynamic experiments, the values of shear modulus and the damping ratio significantly decreases and increases respectively. For each stress level, the low-amplitude modulus remains constant, Gmax, prior to overcoming the apparent threshold strain. Beyond this limit soil softening in the soil reduces the amount of shear modulus and increases the damping ratio of soils. It was also observed that increasing the confining pressure causes this behavior to start at a higher strain and reduce the slope of changes. As another part of this study, using unsaturated Triaxial apparatus equipped with bender element, four samples of different sandy soils with different grain size distribution and fine content, with constant void ratio and D50, in confining pressure of 70 kPa, in drying and wetting paths, were investigated. The results show that with increasing fine content, Gmax behaves more similar to the silt and clay and does not follow the suction stress and does not have any upside or downward trend like a clean sand. Some kind of hardening due to changes degree of saturation and soil volume and pre-consolidation stress is the cause of this change in behavior and the rise of Gmax. Also, the behavior of the Gmax in wetting process sometimes experienced an increasing trend beside decreasing
  9. Keywords:
  10. Strain ; Damping Ratio ; Shear Modulus ; Unsaturated Sand ; Grain Size ; Bender Element Test ; Resonant Column-Torsional Shear Apparatus

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