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

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

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

Nishinomiya-ko bridge, Kobe (1995)

Photo by Yashinsky Puente Tubul, Chile (2010)

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

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

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

Rinko Yasaka Bridge, Ugawa River, Niigata (2007) Better performance… Photos by Yashinsky Rinko Yasaka Bridge, Ugawa River, Niigata (2007)

Caltrans’ current practice per Memo to Designer 20-15. 0.67 PULT Crust 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

Issues the Guidelines Team sought to address… Liquefiable Soil Fill 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

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

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

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

+ + Extend test results with numerical modeling… Fill in gaps with judgment… + +

Caltrans Guidelines Limitations Software Options “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

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

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

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

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

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

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

Caltrans Guidelines Performance Criteria Ma Cap Displacement Pile Moment Pile Shear Well confined pilings H/20 Ma SDC 3.6 Well confined abutment pilings 12 inches Poorly confined pilings 2 inches - *H = column height

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