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Numerical Study of the Effect of Liquefaction-Induced Lateral Spreading on a group of piles

Dehnavi, Alireza | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44279 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. The behavior of pile foundations under earthquake loading is an important issue that affects the performance of structures. Design procedures have been developed for evaluating pile behavior under earthquake loading; however, the application of these procedures to cases involving liquefiable ground is uncertain. The performance of piles in liquefied soil layers is much more complex than that of non-liquefying soil layers because not only the superstructure and the surrounding soil exert different dynamic loads on pile, but also the stiffness and shear strength of surrounding soil diminishes over time due to both non-linear behavior of soil and pore water pressure generation. In this research, 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 liquefiable and non-liquefiable soil layers, piles and superstructures on piles head. The multisurface-plasticity model, Yang et al.(2003), which possesses the simulative ability to model the behavior of drained or undrained saturated sands under monotonic or cyclic loadings, is used, while a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Results of a shaking table test on pile foundations are used to demonstrate the capability of the numerical model for reliable analysis of piles under lateral spreading. For this purpose, seismic response of a group of piles subjected to liquefaction-induced lateral spreading is compared with the results of 1-g shake table test. Finally, the verified model is used for parametric study. The parametric study is carried out by varying boundary condition of pile head, thickness of liquefying layer, pile stiffness, ground slope and thickness of non-liquefiable crust. In addition, shadow and neighboring effects are investigated in this study. Parametric study has been conducted in four different cases. The first case consists of a single pile located in an inclined, loose, liquefiable, saturated sandy layer overlying a non-liquefiable layer. In the second case, the ground is three-layered: the intermediate layer is liquefiable while upper and lower layers are not. In the third case, two piles as front and shadow piles are aligned in the direction of lateral spreading while in the fourth one, a set of three piles aligned in a row perpendicular to direction of lateral spreading to study the neighboring effects. The obtained results indicate that the lateral stresses imparted on piles by the flowing liquefiable soil are larger than those predicted by Japan Road Association (JRA) design manual and assumed uniform lateral soil pressures on the piles due to lateral spreading was obtained in the range of 15-30 kPa. It was found that lateral spreading load on individual piles was a function of pile location in the pile group. The shadowing effect reduced lateral
    load on the shadow pile by about 35% and neighboring effect decreased the lateral pressure on the middle pile about 40% of the lateral load on the side pile
  9. Keywords:
  10. Liquefaction ; Fully Coupled Three Dimensional Dynamic Analysis ; Dynamic Behavior Pile ; Lateral Spread ; Shadow Effect ; Neighboring Effect

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