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Investigation on the Effect of Liquefaction-Induced Lateral Spreading on a Flexible Pile Group and Mitigation Measures for These Effects by Physical Modeling

Raisianzadeh, Javad | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 42152 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohesn
  7. Abstract:
  8. Liquefaction-induced lateral spreading is a known cause of severe damages to deep foundations during past earthquakes. Lateral spreading often takes place in gently sloping grounds which consisted of saturated loose cohesionless soil deposits. Several researchers during recent years have been studying the behavior of piles and soil-pile interaction under lateral spreading but there are still many unknowns in this regard. Also with observing catastrophic damages during past earthquakes caused by lateral spreading, developing proper mitigation measures for existing vulnerable piles against this phenomenon is a necessary act. In the present research, the behavior of a 3x3 flexible pile group and soil-pile interaction under liquefaction-induced lateral spreading are studied by the use of large scale shaking table tests. Also mitigation measures consisting of micropiles and stone columns at upslope and downsolpe of the pile group are investigated. A rigid box with dimensions of 3.5x1x1.5 m is used for the experiments of this study. Soil profile in the models consisted of 3 layers all of them have a slope of 7%. These layers are: a dense sand layer with a relative density of 80% at bottom, a liquefiable loose sand layer with relative density of about 15% at middle and a non-liquefiable crust with relative density of about 60% at top. The models were shaken with a sinusoidal base acceleration having a frequency of 3 Hz and amplitude of 0.3g. Base shaking was applied in longitudinal direction, parallel to the models slope. Piles were made of polyethylene (HDPE) pipes for a flexible behavior to model concrete piles in prototype. The piles have been modeled by the use of similitude laws in 1g tests. The results show that the maximum negative bending moment in the lower part of the pile, occurred at the boundary between the liquefiable and dense bottom layers. Also the maximum positive bending moment in the upper part of the pile occurred close to the pile head. The direction of lateral soil pressures depend on the relative movements between the soil and piles. The experiments also indicate that the first row of the pile group at upslope take more loads and bending moments compared to the second and third rows of the group. The use of micropiles had no effect on mitigating of the lateral spreading effects on the piles. On the other hand the use of stone columns was successful in reducing the effects of lateral spreading on piles. In fact stone columns caused significant reduction of the bending moments and displacements in the piles and the lateral soil pressures exerted on them
  9. Keywords:
  10. Stone Column ; Shaking Table Test ; Liquefaction-Induced Lateral Spreading ; Flexible Pile Group ; Micropile

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