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Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils

Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils. Bradley Fleming, Sri Sritharan , & JinWei Huang Iowa State University Kanthasamy Muraleetharan & Gerald Miller Oklahoma University. Modeling Techniques. Finite Element ( OpenSees )

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Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils

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  1. Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils Bradley Fleming, Sri Sritharan, & JinWei Huang Iowa State University KanthasamyMuraleetharan & Gerald Miller Oklahoma University

  2. Modeling Techniques • Finite Element (OpenSees) • Detailed 3D analysis • Used to understand complex interactions between • pile and improved soil • improved soil and unimproved soil • p-y Analysis Method (LPILE) • Simple 2D analysis • Attractive for engineers in industry • Account for improved soil of limited width by applying modification factors to p-y relationships

  3. OpenSees Finite Element Model • Soil “Island” (OpenSeesPL soil mesh generation) • 10.3 m long, 5.15 m wide, and 7.62 m high • 3,450 nodes • 2,492 soilelements • Pile (forceBeamColumn) • 7.23 m total length • 34 beam elements • 5.3 m embedded length • Non-linear fiber section (half of pile) P Clay Sand Contact Elements (BeamContact3D) Soil Elements (SSPbrick) ClaySand • PressureIndependMultiYield•PressureDependMultiYield •Gmax = 3250 kN/m2•Gmax = 1.0E+5 kN/m2 • c = 30.5 kN/m2 •φ = 37 deg. • γsat =1.8 ton/m3• γsat =2.0 ton/m3 Soil m1 Pile slave r m2

  4. Pile Head Responses of Full-Scale Test and FEM Unimproved Pile Improved Pile

  5. LPILE Model & Modified p-y Curves

  6. Effective Length • Attenuation of stresses in soil layer Guo and Lee (2001) or 0.05

  7. Equivalent Rigidity • R – Equivalent rigidity (analogous to AE for axially loaded member) • Leff - Length of uniform soil layer • ki – Equivalent stiffness of the p-y curve • S - Stiffness of spring Improved Soil Unimproved Soil

  8. Combined Properties Cont.

  9. p-y Modification Factors JinWei Huang (2011)

  10. Global Response Comparisons (Centrifuge) JinWei Huang (2011)

  11. Global Response Comparisons (Centrifuge) JinWei Huang (2011)

  12. Global Response Comparisons (Centrifuge) JinWei Huang (2011)

  13. Field & LPILE Global Responses JinWei Huang (2011)

  14. Field & LPILE Test Local Responses JinWei Huang (2011)

  15. Conclusions • Both LPILE and OpenSees closely resembles centrifuge and field behavior • OpenSees is an effective analysis tool but requires specialized knowledge and involves high computation costs • LPILE is an attractive tool for engineers and has flexibility to modify p-y curves • The proposed method for modifying p-y curves does well in characterizing the behavior of piles in improved soil of limited width

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