Caltrans Guidelines on Foundation Loading Due to Liquefaction

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

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

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

Nishinomiya-ko bridge, Kobe (1995)

Photo by Yashinsky Puente Tubul, Chile (2010)

Better performance… Shukugawa Bridge, Kobe (1995)

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

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

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

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

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

The team must confront challenging issues… Pile pinning effect Crust – pile cap interaction Estimation of crust displacement Residual strength Static vs. dynamic loading 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 “Since every project has unique aspects, these guidelines should not be used to constrain or replace engineering judgment. ” Software Options Nonlinear moment-stiffness behavior: x. SECTION, XTRACT, LPILE 5, others… Soil-foundation interaction: LPILE 5, w. FRAME, SAP 2000 Slope stability: most commercial codes – no special requirements

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

Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Adjustment for wedge effect Matlock (74) soft clay p-y model with Su = SKres and by Ovensen (1964). 1. 3 e 50 = 0. 05 Matlock w~ 0 fwidth 1 pgroup =(psingle )(Npiles p) or solution Fult based on)(m log-spiral pgroup =(psoft clay)(Npiles) pgroup =(psingle)(N 1 piles)(GRF) fdepth Crust loads applied through imposed soil displacement profile mp = 0. 0031 N + 0. 00034 N 2 0 (Zc –D)/T 3 0 0 WT/T LPILE 5 is limited to a single pile analysis 14

Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Pile stiffness Crust loads applied through imposed soil displacement profile Linear case: EIgroup =(EIsingle)(Npiles) Nonlinear case: (See plot…) Stiffness (EI) (fa, Ma) Moment Mmax fa= 12 fy Ma = 1. 1 Mmax fy Curvature fa Moment 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 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

Caltrans Guidelines Unrestrained ground displacement case: Equivalent Nonlinear Static Analysis Approach Crust loads applied through imposed soil displacement profile Inertial Loads Vi = H M o V Mo H Mi =Mo (LPILE 5: Mi 0) Fcapi=0. 65 PGA mcap Abutment Case: assume inertial loads are zero 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 Crust loads applied through imposed soil displacement profile LPILE 5 is limited to a single pile analysis

Caltrans Guidelines Performance Criteria Cap Displacement Pile Moment Pile Shear Well confined pilings H/20 Ma SDC 3. 6 Well confined abutment pilings 12 inches Ma SDC 3. 6 Poorly confined pilings 2 inches - - *H = column height

Caltrans 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