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Liquefaction: Behavior Evidence, Prediction, and Prevention. Richard P. Ray, Ph.D, P.E. Today’s Menu. What is Liquefaction ? How is it expressed ? Can we estimate liquefaction potential ? Can we prevent it from happening or reduce its impact ?. What is it.

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Presentation Transcript
today s menu
Today’s Menu
  • What is Liquefaction ?
  • How is it expressed ?
  • Can we estimate liquefaction potential ?
  • Can we prevent it from happening or reduce its impact ?
what is it
What is it
  • Worm’s eye view - Physical Behavior
  • Professor’s eye view - Laboratory and Analytical Approach
slide7

a

b

c

Worm’s eye view

expression of liquefaction
Expression of Liquefaction
  • Sand boils and flows – free-field
  • Landslides – static lateral stress
  • Foundation Failures – surface loadings
slide23

Evaluating Liquefaction Potential

  • Empirical Methods SPT, CPT
  • Stress or Strain-Based Simplified
  • Effective Stress Time History Models
  • Probabilistic Methods
slide24

Evaluating Liquefaction Potential

Compare Earthquake Load to Soil Resistance

Stress Based

Strain Based

  • Seed & Idriss
  • One Dimensional Response Analysis
  • Laboratory Stress Cyclic Testing
  • Dobry et al
  • One Dimensional Response Analysis
  • Laboratory Strain Cyclic Testing
slide25

Seed & Idriss Simplified Method

FS=Resistance/Load

Resistance = res = fn( SPT Blow Count,

Earthquake Mag,

Percent Fines)

Load = cyc = fn( Earthquake Accel,

Vertical Stress)

slide26

Load Equation, Seed & Idriss Simplified Method

  • Divide profile into segments (~2ft.)
  • Compute  v , rd for each segment
  • Compute  cyc for each segment
slide29

Resistance Equation, Seed & Idriss Simplified Method

  • Use same depth segments (~2ft.)
  • Compute ’vfor each segment
  • Compute CSR for each segment
  • Compute res for each segment
slide30

Resistance Equation, Seed & Idriss Simplified Method

  • CSR = Cyclic Stress Ratio res/’v
  • CSR based on SPT N160 values
  • CSR influenced by Percent Fines

Therefore

  • Must correct N blow counts
  • Must account for Percent Fines
slide33

Resistance Equation, Seed & Idriss Simplified Method (Alternatives)

  • CSR = Cyclic Stress Ratio res/’v
  • CSR based on CPT =>SPT N160 , or
  • CSR based on Vs => SPT N160
slide34

Loading Conditions, Dobry et al Simplified Strain Method

  • Divide profile into segments (~2ft.)
  • Compute  v , rd for each segment
  • Compute cyc for each segment (iterative procedure)
slide35

Liquefaction Resistance, Dobry et al. Simplified Strain Method

  • Perform strain-controlled laboratory tests at several stages of cyc-lab to measure number of cycles to liquefaction N(l,)
    • At cyc = cyc-lab compare Neqto N(l,)
    • If Neq >N(l,) liquefaction possible
    • If Neq <N(l,) liquefaction not possible
slide36

Settlement During Liquefaction, Dobry et al-Castro Method

  • Uses correlation of cyc to vol for dry and saturated sands (SP, SP-SC, SC)
  • For every profile segment use cyc to find vol
  • Multiply vol times segment height to get segment settlement contribution
  • Add all segment contributions for settlement estimate at surface.
slide38

Alternative Methods for Liquefaction Potential Estimation

  • Empirical Approach, Cone Resistance
  • Empirical Approach, Shear Wave Velocity
  • MOC 1-D Analysis
prevention control
Prevention/Control
  • Soil modification
  • Reduced Loads
  • Drainage (pore pressure relief)