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Numerical Modeling of the Bearing Capacity of Suction Caisson by Finite Element Method

Hejazian, Maryam | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40587 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mahdi
  7. Abstract:
  8. Suction caisson is a relatively new technology which was introduced about 30 years ago for the first time and after several investigations, was found its position in the oil industry and construction of anchorages, during previous decade. So nowadays, it is the most effective and economical choice as the mooring of offshore structures in comparison with the other foundations. Suction caisson is a hollow cylinder with an open bottom and a closed top. After placement on the seafloor, the caisson first penetrates into the soil by its self weight and then inserts into the ground by pumping water out of it. Although many researchers have attempted to understand the behavior of suction caissons by means of field tests, laboratory tests and numerical simulations, but several issues and uncertainties related to capacity estimation, are still not resolved. So, as the estimation of the ultimate capacity of suction caisson, is a critical issue in design and application of this new technology, the objective of this study, is to develop a stronger computational framework for more exact capacity estimation of suction caissons under different load inclinations, with various aspect ratios. In this investigation, the three dimentional analysis of the pull-out process of suction caisson was carried out in clay soil and under undrained conditions, using finite element method by Plaxis 3D Foundation computer program. The soil was modeled with saturated porous elements and the caisson was discretized using impermeable rigid elements, also for simulating the nonlinear behavior of clay soil, mohr-coulomb failure criterion was selected. For verifying the validity of the numerical model, Several experimental results were used and then a number of curves were presented for the more exact estimation of the pull-out capacity of suction caissons. In general good agreement was found between calculated and measured caisson capacities, Thus verifying the validity of the presented curves for capacity estimation of suction caissons with different aspect ratios. Finally, the results of the numerical model were compared with the results of the existing limit equilibrium methods to specify the ability of these methods in estimating the ultimate capacity of suction caissons. Therefore, the results of this research can help in more exact design and application of this new technology as the anchorage of large offshore structures.

  9. Keywords:
  10. Finite Element Method ; Three Dimensional Analysis ; Suction Caisson ; Pullout Capacity ; Undraind Conditions

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