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Caltrans Guidelines on Foundation Loading Due to Liquefaction Induced Lateral Spreading

Caltrans Guidelines on Foundation Loading Due to Liquefaction Induced Lateral Spreading. Tom Shantz , Caltrans. 2010 PEER Annual Meeting. PEER TEAM. PEER Guidelines. Scott Ashford (OSU) Ross Boulanger (UCD) Scott Brandenberg (UCLA). Project Participants and Organization.

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Caltrans Guidelines on Foundation Loading Due to Liquefaction Induced Lateral Spreading

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  1. Caltrans Guidelines on Foundation Loading Due to Liquefaction Induced Lateral Spreading Tom Shantz, Caltrans 2010 PEER Annual Meeting

  2. PEER TEAM PEER Guidelines Scott Ashford (OSU) Ross Boulanger (UCD) Scott Brandenberg (UCLA) Project Participants and Organization CALTRANS TEAM Tom Shantz Internal Review Team Caltrans Guidelines

  3. Lessons from history…. Source: ce.washington.edu Showa Bridge, Niigata (1964)

  4. Nishinomiya-ko bridge, Kobe (1995)

  5. Photo by Yashinsky Puente Tubul, Chile (2010)

  6. Better performance… Shukugawa Bridge, Kobe (1995)

  7. Better performance… Photos by Yashinsky Heisei Bridge, Sabaichi River, Niigata (2007)

  8. Better performance… Photos by Yashinsky Kaiun Bridge, Sabaichi River, Niigata (2007)

  9. Better performance… Photos by Yashinsky RinkoYasaka Bridge, Ugawa River, Niigata (2007)

  10. Caltrans’ current practice per Memo to Designer 20-15. Crust 0.67 PULT Liquefied Dense • liquefied soil modeled as factored p-y curves (0.10 p-multiplier) • 67% of the ultimate passive crust load is applied to the cap • no inertial loads are considered • performance criteria: piles remain elastic

  11. Issues the Guidelines Team sought to address… Fill Liquefiable Soil Dense Soil • Crust load–deformation behavior. How much deformation to reach ultimate passive pressure? Adjustments for non-plane strain behavior. • Prediction of crust displacement. • Potential restraining effect of the foundation. • Potential restraining effect of the superstructure. • Contribution of inertial loads to the foundation displacement demand. • More specific performance criteria

  12. The team must confront challenging issues… Pile pinning effect Crust – pile cap interaction Residual strength Static vs. dynamic loading Estimation of crust displacement Kinematic and inertial load combination

  13. Strategy: Where possible, rely on test results. NIED Shake Table: Elgamal (2003) UC Davis centrifuge: Boulanger, Chang, Brandenberg, Armstrong, and Kutter (2006)

  14. Field testing… Port of Takachi Tests by Ashford (2002)

  15. Extend test results with numerical modeling… Fill in gapswith judgment… + +

  16. Caltrans Guidelines Limitations “Since every project has unique aspects, these guidelines should not be used to constrain or replace engineering judgment.” Software Options Nonlinear moment-stiffness behavior: xSECTION, XTRACT, LPILE 5, others… Soil-foundation interaction: LPILE 5, wFRAME, SAP2000 Slope stability: most commercial codes – no special requirements

  17. Caltrans Guidelines Two design cases considered… Fill Liquefiable Soil Dense Soil Foundation restrained ground displacement Unrestrained ground displacement

  18. Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile 1 mp = 0.0031N + 0.00034N2 1 Fultbased on log-spiral solution fdepth pgroup =(psingle)(Npiles)(mp) or pgroup =(psoft clay)(Npiles) fwidth 0 Adjustment for wedge effect by Ovensen (1964). Kw ~ 1.3 0 (Zc –D)/T 3 Matlock pgroup =(psingle)(Npiles)(GRF) Matlock (74) soft clay p-y model with Su = Sres and e50 = 0.05 0 0 WT/T 14 LPILE 5 is limited to a single pile analysis

  19. Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile Pile stiffness Linear case: EIgroup =(EIsingle)(Npiles) Nonlinear case: (See plot…) Mmax (fa,Ma) Stiffness (EI) fa= 12 fy Ma = 1.1 Mmax Moment Moment fy Curvature fa LPILE 5 is limited to a single pile analysis

  20. Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile xi Kax,ni Class 100 pile: Kax = 0.75 (400 kips) / 0.25 in = 1200 kips/in LPILE 5 is limited to a single pile analysis

  21. Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile Inertial Loads H Mo Vi = H Mi=Mo(LPILE 5: Mi Mo V Fcapi=0.65 PGA mcap 0 ) Abutment Case: assume inertial loadsare zero LPILE 5 is limited to a single pile analysis

  22. Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile Combination of kinematic and inertial loading Combination of kinematic and inertial loading LPILE 5 is limited to a single pile analysis

  23. Caltrans Guidelines Performance Criteria

  24. Caltrans Guidelines Guideline availability and adoption: The new guidelines will be available on the Geotechnical Services and Office of Earthquake Engineering websites Guidelines official adoption date has not yet been determined. Any questions or concerns, or you can’t find the guidelines, contact me at tom.shantz@dot.ca.gov

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