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 GuidelinesScott Ashford (OSU)

Ross Boulanger (UCD)Scott Brandenberg (UCLA)

PEER TEAM

CALTRANS TEAMTom ShantzInternal Review Team

Caltrans Guidelines

Project Participants and Organization

Showa Bridge, Niigata (1964)

Lessons from history….

Source: ce.washington.edu

Nishinomiya-ko bridge, Kobe (1995)

Puente Tubul, Chile (2010)Photo by Yashinsky

Shukugawa Bridge, Kobe (1995)

Better performance…

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)

Better performance…

Photos by Yashinsky

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

0.67 PULT

Liquefied

Dense

Crust

• 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

Liquefiable Soil

Fill

Dense Soil

Issues the Guidelines Team sought to address…

• 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

Static vs. dynamic loadingEstimation of crust displacement

Residual strength

Kinematic and inertial load combination

Crust – pile cap interaction

Pile pinning effect

The team must confront challenging issues…

NIED Shake Table: Elgamal (2003)

Strategy: Where possible, rely on test results.

UC Davis centrifuge: Boulanger, Chang, Brandenberg, Armstrong, and Kutter (2006)

Port of Takachi Tests by Ashford (2002)

Field testing…

Extend test results with numerical modeling…

Fill in gaps with judgment…

+ +

Caltrans Guidelines

Software Options

Limitations

“Since every project has unique aspects, these guidelines should not be used to constrain or replace engineering judgment.”

Nonlinear moment-stiffness behavior: xSECTION, XTRACT, LPILE 5, others…

Soil-foundation interaction: LPILE 5, wFRAME, SAP2000

Slope stability: most commercial codes – no special requirements

Liquefiable Soil

Fill

Dense Soil

Two design cases considered…

Unrestrained ground displacement

Foundation restrained ground displacement

Caltrans Guidelines

Equivalent Nonlinear Static Analysis Approach

LPILE 5 is limited to a single pile analysis

Crust loads applied through imposed soil displacement profile

Caltrans Guidelines

Unrestrained ground displacement case:

Fult based on log-spiral solution

Adjustment for wedge effect by Ovensen (1964). Kw ~ 1.3

1

00 3

f dept

h

(Zc –D)/T

f wid

th

1

00 14WT/T

pgroup =(psingle)(Npiles)(GRF)

pgroup =(psingle)(Npiles)(mp) orpgroup =(psoft clay)(Npiles)

mp = 0.0031N + 0.00034N2

MatlockMatlock (74) soft clay p-y model with Su = Sres and e50 = 0.05

Equivalent Nonlinear Static Analysis Approach

LPILE 5 is limited to a single pile analysis

Crust loads applied through imposed soil displacement profile

Caltrans Guidelines

Unrestrained ground displacement case:

Pile stiffnessLinear case:EIgroup =(EIsingle)(Npiles)Nonlinear case:(See plot…)

fafy

Mmax (fa,Ma)

Ma = 1.1 Mmax

fa= 12 fy

Curvature

Mom

ent

Moment

Stiffn

ess (

EI)

Equivalent Nonlinear Static Analysis Approach

LPILE 5 is limited to a single pile analysis

Crust loads applied through imposed soil displacement profile

Caltrans Guidelines

Unrestrained ground displacement case:

Kax, ni

xi

K M 144 K ax n i xi 2

Class 100 pile: Kax = 0.75 (400 kips) / 0.25 in = 1200 kips/in

Equivalent Nonlinear Static Analysis Approach

LPILE 5 is limited to a single pile analysis

Crust loads applied through imposed soil displacement profile

Caltrans Guidelines

Unrestrained ground displacement case:

H

VMo

Vi =Mo

H

Inertial Loads

Mi =Mo (LPILE 5: Mi

Abutment Case: assume inertial loads are zero

Fcapi=0.65 PGA mcap

0 )

Equivalent Nonlinear Static Analysis Approach

LPILE 5 is limited to a single pile analysis

Crust loads applied through imposed soil displacement profile

Caltrans Guidelines

Unrestrained ground displacement case:

Combination of kinematic and inertial loading

Combination of kinematic and inertial loading

Cap Displacement Pile Moment Pile Shear

Well confined pilings

H/20 MaSDC 3.6

Well confined abutment pilings

12 inches MaSDC 3.6

Poorly confined pilings

2 inches - -

*H = column height

Performance Criteria

Caltrans Guidelines

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

Caltrans Guidelines

Guideline availability and adoption: