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Numerical Analysis of Dynamic Behavior of Pile Foundations in Non-homogeneous Liquefiable Soils

Ghaffaripour, Omid | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44650 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Pak, Ali
  7. Abstract:
  8. The behavior of pile foundations during earthquakes is one of the most important factors that affect the performance of structures. Therefore, a large number of studies have been performed on the behavior of pile foundations under dynamic loading. A lot of procedures for the analysis and design of piles under earthquake loading have been developed, especially after the earthquakes which took place in 1964 in Niigata and Alaska. They introduced two major mechanisms for the failure of pile foundations in liquefiable grounds: Bending mechanism and buckling mechanism.In this research the focus is the evaluation of pile failure under buckling mechanism. A fully coupled three-dimensional dynamic analysis is carried out to investigate the dynamic behavior of pile foundations in liquefied ground. The numerical model consists of layers of liquefiable and non-liquefiable soils, a pile and a superstructure on the pile head. The critical state bounding surface elastic-plastic sand model, Dafalias and Manzari (2004), which possesses the ability of simulating the behavior of drained or undrained saturated sands under monotonic and cyclic loadings, is used. A fully coupled (u-P) formulation is employed to analyze soil displacement and pore water pressure. Furthermore, in this study, the variation of the coefficient of permeability during liquefaction is taken into account. The coefficient of permeability is related to the excess pore water pressure ratio.It increases as the pore water pressure builds up and decreases by the dissipation of pore pressure. In order to verify the results obtained from the numerical model, they are compared with the results of some centrifuge tests on pile foundations in liquefiable soils.After verification of the model, it is used for a parametric study. The parametric study is carried out on two general models which represent two approaches for reducing the buckling potential of the piles in liquefied soils. In the first model, the upper layer of the soil profile is compacted, and as a result, it has lost the liquefaction susceptibility. In the second model, the water table elevation is lowered, so the upper layer of the soil profile is dry and cannot liquefy.According to the results obtained from the study, it is concluded that an end bearing pile whose total length is embedded in a liquefiable soil layer, will buckle under a vertical load equal to or greater than the elastic buckling load during earthquake loading. Moreover,in the parametric study it is observed that both approaches have a favorable effect in reducing the pile head horizontal displacement and preventing the pile from buckling. Although there is no considerable difference in their performance, taking into account the practical and economical considerations, the compaction of the surface layer is preferred
  9. Keywords:
  10. Liquefaction ; Fully Coupled Three Dimensional Dynamic Analysis ; Pile Buckling ; Horizontal Displacement of Pile Head ; Dynamic Behavior Pile

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