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

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
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
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
Pile Head Responses of Full-Scale Test and FEM

Unimproved Pile

Improved Pile



Effective length
Effective Length

  • Attenuation of stresses in soil layer

Guo and Lee (2001)

or

0.05


Equivalent rigidity
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
Combined Properties Cont.


P y modification factors
p-y Modification Factors

JinWei Huang (2011)



Global response comparisons centrifuge1
Global Response Comparisons (Centrifuge)

JinWei Huang (2011)


Global response comparisons centrifuge2
Global Response Comparisons (Centrifuge)

JinWei Huang (2011)


Field lpile global responses
Field & LPILE Global Responses

JinWei Huang (2011)


Field lpile test local responses
Field & LPILE Test Local Responses

JinWei Huang (2011)


Conclusions
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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