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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 [email protected]
Caltrans Guidelines
Guideline availability and adoption:
