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Physical Modeling of Effect of Liquefaction-Induced Lateral Spreading on Single Piles

Torabi, Hooman | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40722 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Pile foundations suffered severe damages during the past earthquakes in all around the world. These damages were more severe in laterally spreading grounds and they mostly have been observed in gently sloping grounds and coastal areas. In these cases, Pile foundations not only are subjected to structures inertial loads and kinematic loads of liquefied soil but also lateral spreading intensifies damages. Thus, in the recent decade, several researches have been conducted to investigate the behavior of pile foundations in liquefiable and laterally spreading grounds, however, some uncertainties still remain in modeling of soil-pile interaction. In this study, the effects of liquefaction- induced lateral spreading on single piles is simulated using shaking table test. The rigid wall container of model consists of bottom non-liquefiable and top liquefiable layer with 6% inclination. Due to low level of confining stress in 1g models and its effects on stress-strain behavior of granular soils in liquefaction phenomena, a sand rainer has been developed to construct a liquefiable layer with a relative density of 10-20%. Model includes some single piles and in single or group positions made of aluminum. These piles are modeled based on a design using JRA (2002) code. The input motion is a sinusoidal dynamic excitation with PGA of 0.2g. The shaking is in the same direction of that for lateral spreading. Analysis of the test results indicates that liquefaction affects level and frequency content of acceleration in liquefiable layer. The magnitude of bending moment in piles decreases by moving from base to pile head, and the level of bending moment increases by onset of lateral spreading. Subgrade reaction was calculated using three numerical methods of which Weighted Residual method seems to have better results. Excess pore water pressure and soil- pile relative velocity are key parameters in soil-pile interaction in laterally spreading grounds. Pore water pressure near piles shows different behavior from that of free field. Considerable reduction in subgrade reaction of trailing pile is evident due to shadow effect of front pile. Comparison of time series of subgrade reaction with that of soil-pile relative velocity reveals close correlation of these two parameters. Thus, soil-pile relative velocity and displacement and soil permeability are crucial parameters affecting soil-pile interaction in laterally spreading grounds.
  9. Keywords:
  10. Liquefaction ; Physical Model ; Shaking Table ; Excess Pore Water Pressure ; Subgrade Reaction Modules ; Lateral Spread

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