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An Investigation On The Effects Of Liquefaction Induced Lateral Spreading on a 3×3 Pile Group Using Shake Table Test and Laminar Shear Box and Consideration of Boundary Conditions on Physical Model Results

Salaripour, Saman | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52319 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Lateral spreading is defined as finite lateral displacement of mildly sloping grounds or those ending in free faces induced by liquefaction. Severe damages of pile groups due to lateral spreading in past earthquakes has been reported. Since earthquake is unavoidable, it is necessary to study the response of piles, especially pile groups, to liquefaction induced lateral spreading. Until now, a number of methods have been developed by researchers for design of deep foundations against lateral spreading, but reported failure of piles in last earthquakes indicates that these methods are associated with high uncertainties. This is due to the lack of laboratory and experimental data to evaluate these methods as well as the lack of a comprehensive understanding of the soil-pile interaction problem. In the present study, the effects of liquefaction induced lateral spreading in a mildly sloping ground on the behavior of a 3×3 pile group were investigated using a large scale laminar box on a shake table. For this purpose, a physical model test with three soil layers including bottom non-liquefiable layer, liquefiable layer and crust layer was conducted and tested using shake table facility of Sharif University of Technology. The physical model was shaken with a 30 cycle sinusoidal base acceleration having a frequency of 3.0 Hz and amplitude of 0.3g and two starting and ending ramps of 3 cycles. Duration of the base excitation was 12.0 sec including two rising and falling parts, each of duration of about 1.0 sec at the beginning and the end of the shaking. The slope of all layers was 4 degrees (7 percent) and the liquefying soil was Firuzkuh sand no.161. The laminar shear box used in this study consisted of 23 steel laminates with inner length, width and height of 306, 172 and 180 cm respectively. Different parameters of soil and pile behavior such as acceleration of soil in free field, acceleration of pile cap, pore water pressure in free field, pore water pressure close to piles, soil lateral displacement in free field, pile cap displacement and bending moment of six piles of the 3×3 pile group were investigated. To study the effects of boundary conditions (box type) on physical model results, the results of the present model test were compared with those of a similar physical model test which was conducted using a rigid box on the shake table of Sharif University of Technology. The rigid box length, width and height was 3.5, 1 and 1.5 m. The thickness of the soil layers, the location of most of the transducers, and the number and material of the piles in the pile group in both tests were identical and comparable. Therefore, the main purpose of this study was to investigate the effects of liquefaction induced lateral spreading on a 3×3 pile group as well as the effects of boundary conditions on the results of the physical model. The results of this study showed that the value and pattern of bending moment applied to the piles are influenced by the location of the pile in the group. The other main result of this study is being investigated for the first time is the significant effect of boundary condition on soil and pile group response. It was found that, the values of soil free field displacement, pile cap displacement and force and bending moment of the pile group in the model with rigid box is larger than those of the model with laminar shear box. This observation is because of the rebound of the material when it hits the rigid wall of the rigid box in addition to the greater reflection of the wave from the rigid walls of the rigid box
  9. Keywords:
  10. Liquefaction ; Lateral Spread ; Pile Group ; Shaking Table ; Laminar Shear Box ; Physical Modeling ; Rigid Box

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