Liquefaction: Behavior Evidence, Prediction, and Prevention

Today’s Menu

• What is Liquefaction

• How is it expressed

• How can we predict its occurrence

• How can we prevent it from happening

What is it

• Worm’s eye view

• Professor’s eye view

Cyclic Mobility

• Normally stable soils cross phase line

• Stress reversals cause it to happen over and over

Expression of Liquefaction

• Sand boils and flows – free-field

• Landslides – static lateral stress

• Foundation Failures – surface loadings

Empirical Approach, Shear Wave Velocity

Empirical Approach, Cone Resistance

dvcyc rg

a max65.0

Stress Reduction vs. Depth

-20

0

20

40

60

80

100

0.000 0.200 0.400 0.600 0.800 1.000

Stress Reduction Factor, rd

Dep

th, f

t

Low

Avg

High

Poly. (Low )

Stress Reduction Factor

N vs taucyc/sigv'

0

0.1

0.2

0.3

0.4

0.5

0 5 10 15 20 25 30

(N1)60

tau

/sig

ma

<5%, Wu

15%, Wu

35%, Wu

<5%, Ray

15%, Ray

35%, Ray

Empirical Strength Based on N, Blow Count

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

0.00 500.00 1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 4000.00 4500.00 5000.00

Series1

Series2

ReachNodes

1

2

3

4

5

Base

SurfaceBaseReach

Layer

dzz¶¶+

1-D Shear Wave

-1.50E+00

-1.00E+00

-5.00E-01

0.00E+00

5.00E-01

1.00E+00

1.50E+00

2.00E+00

0 5 10 15 20 25 30

Time (sec)

Vel

ocity

(ft

/sec

)

5.00E-01

6.00E-01

7.00E-01

8.00E-01

9.00E-01

1.00E+00

1.10E+00

1.20E+00

Ene

rgy

Rat

io

Vel 1

Vel 187

Energy Ratio

-5.00E+02

-2.50E+02

0.00E+00

2.50E+02

5.00E+02

-8.0E-03 -6.0E-03 -4.0E-03 -2.0E-03 0.0E+00 2.0E-03 4.0E-03 6.0E-03 8.0E-03

Shearing Strain (m/m)

Shearing Stress (psf)

Prevention/Control

• Soil modification

• Reduced Loads

• Drainage (pore pressure relief)