DYNAMIC STIFFNESS OF PILES IN LIQUEFIABLE Stiffness by ... foundation stiffness, foundation damping, lateral spreading, ... Dynamic response of nonlinear structures

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  • Research Report Research Project Agreement T9903, Task A4

    Dynamic Stiffness

    by

    Pedro Arduino Steven L. Kramer Assistant Professor Professor

    Ping Li David A. Baska Research Assistant Research Assistant

    Department of Civil and Environmental Engineering University of Washington, Box 352700 Seattle, Washington 98195

    Washington State Transportation Center (TRAC) University of Washington, Box 354802

    University District Building 1107 NE 45th Street, Suite 535

    Seattle, Washington 98105-4631

    Washington State Department of Transportation Technical Monitor Jim G. Cuthbertson

    Chief Foundations Engineer, Materials Laboratory

    Prepared for

    Washington State Transportation Commission Department of Transportation

    and in cooperation with U.S. Department of Transportation

    Federal Highway Administration

    DYNAMIC STIFFNESS OF PILES IN LIQUEFIABLE SOILS

    October 2002

  • TECHNICAL REPORT STANDARD TITLE PAGE1. REPORT NO. 2. GOVERNMENT ACCESSION NO. 3. RECIPIENT'S CATALOG NO.

    WA-RD 514.1

    4. TITLE AND SUBTITLE 5. REPORT DATE

    Dynamic Stiffness of Piles in Liquefiable Soils October 20026. PERFORMING ORGANIZATION CODE

    7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO.

    Pedro Arduino, Steve L. Kramer, Ping Li, David A. Baska

    9. PERFORMING ORGANIZATION NAME AND ADDRESS 10. WORK UNIT NO.

    Washington State Transportation Center (TRAC)University of Washington, Box 354802 11. CONTRACT OR GRANT NO.University District Building; 1107 NE 45th Street, Suite 535 Agreement T9903, Task A4Seattle, Washington 98105-463112. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED

    Research OfficeWashington State Department of TransportationTransportation Building, MS 47370

    Research report

    Olympia, Washington 98504-7370 14. SPONSORING AGENCY CODEKeith Anderson, Project Manager, 360-709-540515. SUPPLEMENTARY NOTES

    This study was conducted in cooperation with the U.S. Department of Transportation, Federal HighwayAdministration.16. ABSTRACT

    This research developed tools and procedures for evaluating the stiffness of pile foundations inliquefiable soils during earthquakes. Previous research on dynamic stiffness performed for theWashington State Department of Transportation resulted in the development of a Manual that providedsimple charts for estimating the stiffnesses of typical pile foundations in soil deposits typical of thoseencountered in Washington state. The tools and procedures developed in the current project were basedon up-to-date models for liquefiable soil and for soil-pile interaction, which obviated the need for many ofthe simplifying assumptions used in the Manual. The tools were developed by updating and extending thecapabilities of two computer programs developed in part during previous WSDOT research studies.

    A greatly improved model for describing the seismic response of liquefiable soil was implementedinto a nonlinear, effective stress site response analysis (WAVE). This model, termed the UWsand model,allows estimation of the response of typical sands to the stresses induced by earthquake shaking. Themodel has the important advantage of being easily calibrated with commonly available data. It capturesimportant aspects of the behavior of liquefiable soils, including the phase transformation behaviorassociated with cyclic mobility that strongly influences free-field response and soil-pile interaction. Themodel has been successfully validated against field observations of soil liquefaction.

    Soil-pile interaction analyses were performed with an extended version of the programDYNOPILE. DYNOPILE was modified to allow different pile head loading conditions, including theattachment of a single-degree-of-freedom structure to the pile head to allow coupled analysis of soil-pile-structure interaction. A Windows-based version of DYNOPILE was developed.

    The modified WAVE and DYNOPILE programs were used to improve and extend the stiffnesscharts for liquefiable soils that were presented in the Manual. WAVE and DYNOPILE can also be appliedto site-specific evaluation of dynamic pile stiffness by using the same procedures used to develop theimproved charts.

    18. DISTRIBUTION STATEMENT

    Piles, liquefaction, foundation stiffness, foundationdamping, lateral spreading, seismic response

    No restrictions. This document is available to thepublic through the National Technical InformationService, Springfield, VA 22616

    19. SECURITY CLASSIF. (of this report) 20. SECURITY CLASSIF. (of this page) 21. NO. OF PAGES 22. PRICE

    None None

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    DISCLAIMER

    The contents of this report reflect the views of the authors, who are responsible

    for the facts and the accuracy of the data presented herein. The contents do not

    necessarily reflect the official views or policies of the Washington State Transportation

    Commission, Department of Transportation, or the Federal Highway Administration.

    This report does not constitute a standard, specification, or regulation.

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    CONTENTS Chapter 1. Dynamic Stiffness of Piles in Liquefiable Soils .................................. 1 Background................................................................................................................ 2 Purpose of Research................................................................................................... 2 Organization............................................................................................................... 4 Chapter 2. Soil Liquefaction ................................................................................... 5 Terminology............................................................................................................... 5 Initiation of Liquefaction ........................................................................................... 6 Loading .......................................................................................................... 7 Resistance ...................................................................................................... 7 Evaluation ...................................................................................................... 8 Liquefaction and Cyclic Mobility.............................................................................. 10 Summary .................................................................................................................... 13 Chapter 3. Previous Work ...................................................................................... 14 Case Histories of Liquefaction-Induced Pile Damage............................................... 14 Experimental Research .............................................................................................. 17 Centrifuge model testing................................................................................ 17 Shaking table model testing........................................................................... 19 Analytical Research ................................................................................................... 20 Horne (1996).................................................................................................. 22 Free-field response analysis........................................................................... 22 Kinematic pile response analysis ................................................................... 22 Wu and Finn (1997) ....................................................................................... 23 Lok et al. (1998)............................................................................................. 25 GeoSpectra Manual.................................................................................................... 26 Discussion.................................................................................................................. 28 Chapter 4. Free-Field Response Analysis .............................................................. 30 UWsand Soil Model................................................................................................... 31 Yield function ................................................................................................ 31 Hardening law................................................................................................ 32 Flow rule ........................................................................................................ 33 Stress reversals............................................................................................... 33 Undrained analysis......................................................................................... 34 Examples........................................................................................................ 35 Calibration of UWsand Model................................................................................... 36 Miscellaneous parameters.............................................................................. 38 Number of cycles that occur until initial liquefaction ................................... 40 Rate of pore pressure generation ................................................................... 41 Effects of (N1)60 ............................................................................................. 41 Effects of static shear stress ........................................................................... 54 Validation of UWsand/WAVE Model....................................................................... 59

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    Permanent ground surface displacements..............................................