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Liquefaction Effects on (a) Individual and Group of Capless Piles and (b) Group of three Piles under Real and Artificial Earthquakes

Sabouri, Marjan | 2014

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 45875 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. In the areas where the soil beneath the foundation is made of loose to semi-consolidated sand or noncohesive silts, Buildings and bridges are usually built on the pile foundations. One important issue that must be considered in the design of piles in saturated sandy soils, is liquefaction potential of saturated sandy soil under earthquake loads. During the earthquake, saturated sandy soil faces the sudden loss of shear strength in other word it liquifies . Liquefied Soil acts like a viscous fluid. This behaviour considerably increases the soil deformation and consequently the widespread disruption of soil layers, causes large deformation and applies great amount of forces on the piles which results in damage or failure of the pile if not properly designed.
    In recent years the Laboratory of Civil Engineering Department of Sharif University of Technology, has conducted some tests on a physical model with shaking table to study the effects of liquefaction on a single pile and group of piles. In this study the results obtained from aforementioned physical models, have been analyzed and liquefaction effects on (a) individual capless pile and group of capless piles under an artificial earthquake and (b) group of three piles under real and artificial (lab generated) earthquake has been studied.In these tests, stiff piles are used which are placed in a two layers of sands; the lower dense and non-liquefiable layer and the upper loose and susceptible to liquefaction layer. In the experiments, for recording values of acceleration, pore water pressure, displacement and bending momment, relevant instruments have been placed in free field, on the soil surface, around and on the piles. In this study, the measured data and the results of these experiments were analyzed in the forms of time history of acceleration, excess pore-water pressure, bending moment and bending moment profiles of piles , pressure and lateral displacement along piles and cyclic P-Ycurves.Based on the analysis carried out in this study on liquefaction effects on individual and group capless piles using an artificial earthquakes, piles of the model behaved like a cantilever beam and the maximum bending moment occured at the ends pointsof the piles. Shadow effect reduces the amount of bending moment of the piles. neighboring effect reduces the bending moment in the pile group compared to a single pile. In study of the triple pile (group of three pile) under real and artificual earthquakes load, restraining effect of fixed end is higher than that for the head restricted by the pile cap and thus the point of maximum bending moment occurs near the bottom of the piles .In both experiments, liquefaction occurs later adjacent to the pile than that for the free field and drainage of pore-water pressure occurs faster.Bending moment of piles reaches to its maximum when liquefaction triggers and then decrease, after occurrence of liquefaction, the slope of the P-Y curves are reduced.Therforethe stiffness and strength of the soil decrease and the softening phenomenon occurs
  9. Keywords:
  10. Liquefaction ; Pore Water Pressure ; Bending Moment ; Physical Model ; Single Pile

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