Understanding and improving the seismic behavior of pile foundations in soft soils
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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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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


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


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


Pile Head Responses of Full-Scale Test and FEM

Unimproved Pile

Improved Pile


LPILE Model & Modified p-y Curves


Effective Length

  • Attenuation of stresses in soil layer

Guo and Lee (2001)

or

0.05


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


Combined Properties Cont.


p-y Modification Factors

JinWei Huang (2011)


Global Response Comparisons (Centrifuge)

JinWei Huang (2011)


Global Response Comparisons (Centrifuge)

JinWei Huang (2011)


Global Response Comparisons (Centrifuge)

JinWei Huang (2011)


Field & LPILE Global Responses

JinWei Huang (2011)


Field & LPILE Test Local Responses

JinWei Huang (2011)


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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