An Investigation on the Effects of Liquefaction-Induced Lateral Spreading on Deep Foundations Using Finite Difference Method

Afzal Soltani, Sina | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50288 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Liquefaction is an important phenomenon in geotechnical engineering which can cause severe damages to structures. Liquefaction-induced lateral spreading is defined as the lateral displacement in mild slopes or level grounds ending in free faces (such as quay walls) triggered by liquefaction in subsurface soil layers. During recent years, extensive studies have been conducted around the world documenting liquefaction induced lateral spreading and its effects on deep foundations. In the present study, a series of shaking table experiments which were previously conducted at Sharif University of Technology are numerically simulated using the three dimensional finite difference based program, FLAC3D. This study is aimed to numerically model a number of physical model tests, to investigate the effect of lateral spreading on piles and pile groups and also to assess the capability of an advanced critical state two-surface plasticity model in predicting soil and pile responses to lateral spreading. Changes in permeability of the soil layers during the shaking are also accounted for using the software’s built-in programming language, FISH. Numerical results showed that the onset of liquefaction occurs after just a few cycles from the beginning of the shaking and the main share of ground lateral movement takes place during the first few seconds of dynamic excitement which is a common phenomenon in physical model testing of loose liquefiable layers. Elastic rebound of the piles when they reach to their maximum lateral displacement was simulated using nonlinear springs in shear and normal directions along the length of the piles. In this springs, yield strength is dependent on the effective confining stress in adjacent zones. Effect of pile stiffness and its location relative to the other piles in the group on response of the piles to lateral spreading are also discussed. It was observed that bouncing back of the stiffer piles begins sooner relative to that of the flexible ones. Flexible piles showed relatively consistent movements with the surrounding soil which resulted in neglegible ground upheave on the upslope side of the piles; whilst upheave of about 4 centimeters (in model scale) was observed on upslope side of the stiff piles. Maximum bending moment at the end of the middle pile in each row of the pile group is shown to be smaller relative to the side piles in the same row (neighboring effect); in a similar way, larger bending moments was observed in the front piles (on the upslope side of the group) relative to the downslope piles (shadow effect). In general, comparison of the experimentally obtained data and the simulation results, showed decent accuracy of the numerical predictions
  9. Keywords:
  10. Fully Coupled Analysis ; Liquefaction ; Lateral Spread ; Finite Difference Method ; Earthquake ; FLAC Software ; Critical State Two-Surface Plasticity Model ; Pile Group

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