Effect of Lateral Spreading Due to Liquefaction on Piles, Numerical Simulation with OpenSees

Ghasemi Fard, Ali | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48148 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Lateral spreading due to liquefaction and resulting destruction of buildings is important in Iran because of high seismicity and important infrastructure near south and north coasts of Iran. Lateral spreading is vast lateral movement of sloping ground or level ground ending in an opening like river which is caused by earthquake inducedliquefaction. For considering the effects of lateral spreading during design of deep foundations of structures in a susceptible area, one needs to determine the lateral loads on piles under lateral spreading. Present study investigates the behavior of a 3x3 pile group against lateral loads due to lateral spreading with numerical methods using OpenSees software. Laboratory tests of the effect of lateral spreading on pile groups using shake table have been performed at Sharif University of Technology during 2010-11 in a rigid box with dimensions of 3.5m x 1m x 1.5m. The laboratory test used for verification of the numerical model of this study is the test done on 3x3 pile group tested under a sinusoidal motion with a maximum acceleration of 0.3g Soil layers in that experiment included a liquefiable layer with a thickness of 1m which was located between two non-liquefiable layers, an upper layer with a thickness of 25cm and a lower layer with a maximum thickness of 25cm. The inclination of discribed layers was 4o. The numerical model of this research was first verified with the described physical model and then a parametric study in prototype dimensions was performed. Comaprison of the results from numerical model with that of physical model showed that predictions of excess pore water pressure and bending moment of piles using numerical method are acceptable. Also the maximum displacement of the soil profile at the end of the test has about 10% difference between the measured values in physical model and the results of conducted numerical model. Parametric studies include the effects of the thicknesses of the liquefiable and upper non-liquefiable layers and the effect of pile stiffnesson the response of 3x3 pile group to lateral spreading. The Increasing liquefiable layer thickness increases the maximum displacement of the soil profile and bending moment of the piles. For example increasing liquefiable layer thickness from 8m to 12m causes a 5 times increase in maximum soil profile displacement and a 12 times increase in bending moment of upstream middle pile at interface of upper non-liquefiable layer and the liquefiable layer. By decreasing surface layer thickness the value of positive and negative pile moment and pile cap displacement increases. For example decreasing the thickness of surface layer from 2m to 1m causes a 2 times increase in positive and negative moment of upstream middle pile. Also decreasing surface layer thickness from 2m to 0 causes a 60% increase in the pile cap displacement. Reducing pile stiffness causes reduction in bending moment of the piles. For example one fold reduction in pile stiffness causes a 40% reduction in bending moment of the piles
  9. Keywords:
  10. Liquefaction ; OpenSees Software ; Numerical Model ; Pile Group ; Lateral Spread

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