1 interpretation and visualization of model test data for slope failure in liquefying soil bruce l....

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Interpretation and Visualization of Model Test Data for Slope Failure in

Liquefying Soil

Bruce L. Kutter

Erik J. Malvick

R. Kulasingam

Ross Boulanger

UC DAVIS

US-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures against Liquefaction

US National Science Foundation (Grant Number: CMS-0070111)

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Concepts: Void redistribution – contraction and dilation

(A)Dilating element: vin > vout

(B) Constant volume element: vin ~ vout

(C) Contracting element: vin < vout

Ht

Hb

AB

C

Example: impermeable layer covering a liquefiable layer

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Phase trasformation line limits the pore

pressure build up --- until flow failure

occurs

In itia lF ina l

e C SL

A

C

A

C

Concept:

Ht

Hb

AB

C

A

C

LocalizationFlow

dilatant

contractive

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Hypotheses

Pore water tends to accumulate at the interface of a relatively impermeable layer that covers a liquefying sand layer. The accumulation permits the saturated soil to dilate in this region and consequently, shear strains may localize near the interface.

The localization leads to an increase in the magnitude of deformations, and could lead to flow failure

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Before shaking

After Motion A

After Motion B(Longer duration)

Test #2 on the small centrifugeKulasingam et al.(2001)

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EJM01_217

Large Centrifuge Model Test

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Before

After 2 Shakes

0.38 m model

14 m prototype

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Before

After 2 Shakes

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Concentrated Shear Zone Below Silt-Sand Interface.

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Displacement Profile

12

Basic Diagram, Linear Potentiometers

L1 L2L3

L4,L5,L6

L7L8L9L10

ShakingNS

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Basic Diagram, Accelerometers

ACC =

ShakingNS

A1, A3

A2

A31

A29, A30

A32

A4A5 A6 A7 A8

A9 A10A11 A12

A13 A14 A15 A16 A17 A18

A19 A20

A21

A22

A23 A24A25

A26A27

A28

Grid Square = 10 cm Model Scale

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Selected results

0 20 40 60 80 100 120 140 160 180 200Tim e (s)

0

0Acc

ele

ratio

ntic

k =

0.2

g

0

0

Ru

tick

= 0

.2

0

Dis

pla

cem

ent

tick

= 0

.2 m

0

1 L3

L1

P23

A24

A27

A20

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Basic Diagram, Pore Pressure Transducers

PPT =

ShakingNS

P1 P2 P3 P4P5 P6 P7

P8 P9

P10 P11 P12 P13 P14 P15 P16P17

P18P19

P20

P21 P22 P23

P24 P25

P26

P27


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Surface

Silt Plane

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Procedure to calculate volumetric strains from measured pwp

1

1 )()(

i

ieie

win h

uukv

)(5.0 1

ii

inoutv

hh

vv

dt

d

Darcy’s law, based on ue measured in centrifuge

from conservation of volume

hi is the spacing of the sensors;

Volumetric strain rate is proportional to the second derivative of the pore water pressure

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Basic Diagram, Pore Pressure Transducers

PPT =

ShakingNS

P1 P2 P3 P4P5 P6 P7

P8 P9

P10 P11 P12 P13 P14 P15 P16P17

P18P19

P20

P21 P22 P23

P24 P25

P26

P27


Array 4

Array 6

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Array 4silt

Array 6

silt

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Effect of Void Redistribution on Residual Shear Strength (Sr)

Seed (1986) argued that Sr values back-calculated from case histories of flow failures implicitly accounted for any effects that void redistribution and/or other factors may or may not have had.

Mechanism B by NRC (1985) - Example of potential void redistribution within a globally undrained sand layer.

Seed & Harder (1990)

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Conclusions• Water tends to flow upward during liquefaction and this water may

accumulate in a dilating shear zone beneath an impermeable boundary. • Pore pressures in a dilatant stable slope tend to stabilize such that

mob=33o (~“phase transformation”); limiting ru values depend on the magnitude of shear stress.

• Critical combinations of shaking intensity, relative permeabilities, layer thicknesses, and densities determine whether localization will occur.

• It is virtually impossible to perform a systematic study of the all parameters affecting void redistribution from field case histories. Model testing is the only way!

• The use of even more instrumentation in model tests and automated visualization tools will improve the resolution of detail.

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Conclusions (2)• Procedures were developed to improve contour plot by

forcing contours to match estimated boundary conditions – Drained boundary: u = 0– Impermeable boundary: normal hydraulic gradient = 0– For pore pressure ratio: ru= ru(nearest transducer)

• The second derivative of measured pwp distribution was used to calculate volumetric strain rate distribution. Small errors in water pressure measurement can lead to larger errors in the second derivative. Nevertheless, the results seem meaningful.

• Visualization and analysis of pore pressure data from a large centrifuge test provides a lot of detail that is difficult to obtain by any other method.

CYCLIC SETTLEMENT AND SLIDING OF SEAWALLS

Randolph R. Settgast

Input Motions

0.1 10.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 3

Period (s)

0

2

4

6

PS

A (

g)

0.5 g Kobe0.4 g 3 Hz

0.6 g 3 Hz

1

0

-1

Acc

. (g)

0.6 g 3 Hz event

Time (s)4 6 8 10 12 14 16

Acc

. (g)

1

0

-10.5 g Kobe event

Seawall Model Deformation

Cyclic Load-Deformation Response Parameters

• Shear Stress

• * Shear Strain

• S* Axial (Vertical) Strain

• v* Effective Stress

NORTH

DISPLACEMENT TRANSDUCER (HORIZONTAL)

DISPLACEMENT TRANSDUCER (VERTICAL)

LEGEND

ACCELEROMETER (HORIZONTAL)

ACCELEROMETER (VERTICAL)

PORE PRESSURE TRANSDUCER

EARTH PRESSURE TRANSDUCER

Cyclic Load-Deformation Response

-40

-20

0

20

40

(

kPa)

(a) vs v*

0 50 100 150v* (kPa)

-0.015

-0.010

-0.005

0.000

0.005

S*

(c) S* vs v*

(b) vs *

-0.01 -0.00 0.01 0.02 0.03 0.04*

(d) S* vs *

Effects of Substratum Improvement

0.47B0.55B

B

Dr 95 %Dr 50 %

0 10 20 30 40 50 60 70 80 90 100

Improved Area (%B)

0

100

200

300

400

500

Cum

ulat

ive

Lat

eral

Dis

p. (

mm

)

Small Strain Events0.1 g Sine Wave0.35 g Sine Wave0.1 g Sine Wave0.5 g Sine Wave0.1 g Sine Wave0.5 g Kobe Motion

1 interpretation and visualization of model test data for slope failure in liquefying soil bruce l....

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