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Effects of Liquefaction on 2×2 and 3×3 Stiff and Flexible Pile Groups

Goudarzi, Anahita | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45876 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Liquefaction has a profound effect on buildings, bridges, buried pipes and other engineering structures. This phenomenon can lead to the sliding of huge earth masses, submersion and bending of substantial structures, uplift of buried light structures and collapse of retaining walls. In recorded earthquakes, liquefaction has caused major damage to structures and deep foundations, proving that pile foundations are not designed to withstand at liquefaction condition. Considerable damages in pile foundations due to liquefaction in destructive earthquakes has called for extensive study and research concerning the behavior and response of piles under the influence of liquefaction, resulting in investigations on a global scale. Nonetheless, there are still some ambiguities in this area to be dealt with more deeply. The present study examines the results of large scale physical models constructed on the shake table for 2×2 and 3×3 stiff pile groups and 3×3 flexible pile group in liquefiable soils. In these tests, the pile groups embedded in three-layer soil profile, including dense non-liquefiable bottom layer, liquefiable intermediate layer, and the top dense non- liquefiable layer. In such tests the effects of different parameters such as the number of piles in a group, the existence of overlaying structures, and the stiffness of piles in groups are evaluated. In order to record the magnitude of acceleration, pore water pressure, displacement, and bending moment, some instrumentations are installed in free field, on the surface of the soil layer, around the model piles and on the piles. In this research, the results are represented as time history of acceleration, excess pore water pressure, bending moment, and also the profile of bending moment, soil pressure, and lateral displacement along the piles, as well as the hysteresis P-Y curves for the piles. The results indicate the reduction of acceleration amplitude as the liquefaction starts, differences in the behavior of excess pore water pressure generated in free field and in surrounding the piles in two cases of stiff and flexible pile groups, and the effect of the non-liquefiable top soil layer on the distribution of bending moment and soil pressure along the piles. The shadow effect of piles in a group is studied that indicates that the bending moment of the pile located in the shadow reduces. The effect of pile neighbarry is also investigated that indicate the reduction in bending moment of the middle pile in a group, compared to the outer piles. The stiffness of pile groups plays a major role in the variations of pore water pressure, pile displacement, distribution of bending moment and pressure
  9. Keywords:
  10. Liquefaction ; Pile Group ; Shaking Table ; Physical Model ; Pore Water Pressure ; Bending Moment ; Lateral Earth Pressure

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