structural engineering and earthquake simulation laboratory sg-1: lateral spreading – observations...

Structural Engineering and Earthquake Simulation Laboratory

SG-1: Lateral Spreading –SG-1: Lateral Spreading –Observations & AnalysisObservations & Analysis

Raghudeep B. & Thevanayagam S.

20 Aug 2007: 9-9:30 AM, NEESR-Workshop

PI: R. Dobry, co-PI’s: A. Elgamal, S. Thevanayagam, T. Abdoun, M. ZeghalUB-NEES Lab: A. Reinhorn, M. Pitman, J. Hanley, SEESL-StaffTulane: Usama El ShamyStudents & Staff: UB (N. Ecemis, Raghudeep B.) and RPI (J. Ubilla, M. Gonzalez, V. Bennett, C. Medina, Hassan, Inthuorn)

Structural Engineering and Earthquake Simulation Laboratory2

OutlineOutline

Review of Test SG-1 Lateral Spreading Observation

Comparisons of LG-0 and SG-1 Highlights – Similarities & Differences (flat versus sloping

ground) Reanalysis of Lateral Spreading

Initiation of spreading – hypothesis Newmark analysis - Sliding Some thoughts

Thoughts on lateral spreading


Review of SG-1 TestReview of SG-1 Test


Review of Test SG-1Review of Test SG-1

Inclined Box (2o) Hydraulic Fill (Dr = 45~55%) 5.58m [18 ft] Deep Saturated Sand Dense Instrumentation Design Base Motion (5s/10s/10s/10s) Uninterrupted Base Motion (5s ~0.01g/3s ~0.05g) Soil Liquefied Large lateral spreading observed


SG-1 Test ConfigurationSG-1 Test Configuration

Top View

Side View


Input Base MotionInput Base Motion

14 16 18 20 22 24 26 28-0.5

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

Time [s]

Hor

izon

tal D

ispl

acem

ent [

cm]

POL1X 5.58m - Tied to the Base Shaker

1st Stage Motion

Damped Motion

Actuator Cut-Off

Data Analyzed in this Range

2nd Stage Motion2 Hz


Base AccelerationsBase Accelerations

14 16 18 20 22-0.2

-0.1

0

0.1

0.2X-Motion of the Base

b1x

14 16 18 20 22-0.2

-0.1

0

0.1

0.2

Acc

ele

ratio

n [g

] b2x

14 16 18 20 22-0.2

-0.1

0

0.1

0.2

Time [s]

b3x

14 16 18 20 22-0.2

-0.1

0

0.1

0.2Y-Motion of the Base

b1y

14 16 18 20 22-0.2

-0.1

0

0.1

0.2b2y

14 16 18 20 22-0.2

-0.1

0

0.1

0.2

Time [s]

b3y

Base Input Motion


Excess Pore Pressure ResponseExcess Pore Pressure Response

0 10 20 30 40 50

0

1

2

3

4

5

6

Average Pore Pressure Profile

Excess Pore Pressure [kPa]

De

pth

[m]

t = 19st = 20st = 21st = 22st = 22.5slimit

0 0.2 0.4 0.6 0.8 1

0

1

2

3

4

5

6

Average ru Profile

De

pth

[m]

ru

t = 19st = 20st = 21st = 22st = 22.5s


Displacement ResponseDisplacement Response

5

15

25

35POL22X at 0m d

x-vertex17

5

15

25

35POL16X at 1.56m d

x-vertex13

5

15

25

35

Ho

rizo

nta

l Dis

pla

cem

en

t [cm

]

POL10X at 3.11m dx-vertex7

5

15

25

35POL5X at 4.4m d

x-vertex4

14 15 16 17 18 19 20 21 22-5

5

15

25

35POL3X at 4.91m d

x-vertex3

Time [s] 0 5 10 15 20 25 30 35

0

1

2

3

4

5

6

Horizontal Displacement [cm]

De

pth

[m]

t = 19st = 20st = 21st = 22st = 22.5s


Shear Strain Shear Strain [Potentiometers][Potentiometers]

14 15 16 17 18 19 20 21 220

5

10

15

L#1-3 at 5.17mL#3-5 at 4.65mL#5-8 at 4.01mL#8-10 at 3.37mL#10-13 at 2.71m

5

10

15

L#13-16 at 1.94mL#16-18 at 1.3mL#18-20 at 0.78mL#20-21 at 0.38mL#21-23 at 0.12m

cyc

ceases and continues

as monotonic shear

cyc

still exists

Time [s]

glob

al [%

]


Accelerations & PWP ResponseAccelerations & PWP Response

0

0.1

0.5

1

0

0.1

0.5

1

0

0.1

Acc

ele

ratio

n [g

]

0.5

1

r u

0

0.1

0.5

1

14 16 18 20 22-0.1

0

0.1

Time [s]14 16 18 20 22

0

0.5

1

0.24m

1.56m

2.32m

3.11m

4.4m

________ Acceleration --------------- ru

Ring Accelerations

Top

Middle

To

0 1 2 3

0

1

2

3

4

5

6

Amplification Factor

De

pth

[m]

Amplification in SG-1

ND Shaking


Lateral Spreading Lateral Spreading MechanismMechanism


Shear StressesShear Stresses

2.5

5

2.5

5

2.5

5

[k

Pa

]

2.5

5

14 15 16 17 18 19 20 21 220

2.5

5

14 15 16 17 18 19 20 21 22

at 0.122m

at 0.381m

at 0.777m

at 1.295m

at 1.936m

at 2.713m

at 3.368m

at 4m

at 4.648m

at 5.166m

Time [s]

Top Rings

Bottom Rings


Factors Conducive for Lateral Spreading: Factors Conducive for Lateral Spreading: LG-0 versus SG-1LG-0 versus SG-1

SG-1

Shear Strain

0

Cyclic

Flow Failure

Strain Accumulation

Monotonic Strength Envelope

Sh

ear

Str

ess

Shear Strain

LG-0


Small Strain Accumulation

• No Static Shear• Very little Strain Accumulation• No Flow observed• Failure termed as Liquefaction

• Non-zero Static Shear• Strain Accumulation until curve hits the strength envelope• Large Flow thereafter and curve follows the envelope• Failure termed as Flow Failure

Lateral spreading begins when cyclic shear stress meets monotonic failure envelope


Triaxial Test Data Triaxial Test Data (no initial shear, Theva 2003)

• e=0.779 (Moist tamping) • e = 0.778 (MT)

• e=0.804 (MT)

Is this what is seen in SG-1?Is hydraulic fill creating meta-stable structure more prone to collapse?Is collapse potential higher if static shear is present (i.e occurs at higher densities)?


Lateral Spread Mechanism Lateral Spread Mechanism [Contd.][Contd.]

0 5 10 15 20-5

0

5Stress Path comparison between LG0 & SG1

'v [kPa]

[k

Pa

]

0-5s LG00-5s SG1 Failure Envelope

Failure Envelope

Lateral spreading begins when cyclic shear stress meets monotonic failure envelope.Soil is not necessarily at liquefied state when lateral spread begins.

Ultimate

int


Flow Begins !!!


Strain Accumulations - Strain Accumulations - ND PhaseND Phase

-1

1

3

5Stress-Strain Behavior in LG0

-1

1

3

5

-1

1

3

5

[k

Pa

]

-1

1

3

5

0 3 6 9 12-3

-1

1

3

5

Stress-Strain Behavior in SG1

0 3 6 9 12

0.15m 0 - 5s_____

1.9m 0 - 5s_____

2.67m 0 - 5s_____

3.35m 0 - 5s_____

4.57m 0 - 5s_____

0.12m

1.94m

2.71m

3.38m

4.65m

[%]

LG-0 SG-1

Little Strain Accumulations in 0-5s More Strain Accumulations in 0-5s


Strain Accumulations Strain Accumulations – – ND & Strong Shaking PhaseND & Strong Shaking Phase

-1

1

3

5Stress-Strain Behavior in LG0

-1

1

3

5

-1

1

3

5

[k

Pa

]

-1

1

3

5

0 3 6 9 12-3

-1

1

3

5

Stress-Strain Behavior in SG1

0 3 6 9 12

0.15m 0 - 5s

5 - 8.5s

_____

_____

1.9m 0 - 5s

5 - 8.5s

_____

_____

2.67m 0 - 5s

5 - 8.5s

_____

_____

3.35m 0 - 5s

5 - 8.5s

_____

_____

4.57m 0 - 5s

5 - 8.5s

_____

_____

0.12m

1.94m

2.71m

3.38m

4.65m

[%]

Small DeformationsLarge Deformations, primarily initiated

by gravitational static shear


Comments on LG-0 Vs SG-1Comments on LG-0 Vs SG-1 Soil degraded faster in SG-1 compared to LG-0 Mostly Cyclic Strains in LG-0; Monotonic strains dominate in

SG-1 Level Ground Soil Strains accumulate @ high ru ~ 0.9-1.0. Sloping Ground Soil Strains accumulate @ low ru (~ 0.6-0.7).

Initial Static shear has a significant influence in initiating large strains.

Cyclic shear in SG-1 degrades the soil sufficiently to a point where the cyclic shear stress meets undrained strength envelope, lateral spreading begins?

Identify lateral spread initiation points from stress-strain curves deduced from acceleration data (next)

Then perform Newmark analysis modified to account for strength degradation


Soil Response @ 1.3m - Soil Response @ 1.3m - AnimationAnimation


14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 1.3mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 1.3m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 1.3m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 1.3m

1.3m

Soil Response & Spreading InitiationSoil Response & Spreading Initiation



14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 0.78mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 0.78m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 0.78m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 0.78m

0.78m


14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 1.94mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 1.94m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 1.94m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 1.94m

1.94m



14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 2.71mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 2.71m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 2.71m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 2.71m

2.71m



14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 3.37mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 3.37m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 3.37m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 3.37m

3.37m



Soil Response @ 4m - Soil Response @ 4m - AnimationAnimation


14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 4mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 4m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 4m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 4m

4m



14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 4.65mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 4.65m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 4.65m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 4.65m

4.65m



14 16 18 20 220

1

2

3

4

5

Time [s]

[k

Pa

]

at 5.17mInitiation

14 16 18 20 220

2

4

6

8

10

12

Time [s]

[%

]

at 5.17m

0 2 4 6 8 10 120

1

2

3

4

5

[%]

[k

Pa

]

- at 5.17m

0 10 20 30 40 500

1

2

3

4

5

'v [kPa]

[k

Pa

]

p-q at 5.17m

5.17m



Mobilized Strength & Friction Angle Mobilized Strength & Friction Angle duringduring Spreading Spreading

Strain-dependent strength and Friction Soil strength equal to the existing stress, from the spread

initiation point onwards Friction angle increases with strain, during spreading

tanf()

(1-ru)’v0

=


Mobilized Friction Angle Mobilized Friction Angle [during sliding][during sliding]

15

30

45

14 15 16 17 18 19 20 21 220

15

30

45

14 15 16 17 18 19 20 21 22

0.78m 1.3m

1.94m 2.71m

Time [s]

0 = 29.4o

0 = 15.88o

0 = 18.05o

0 = 10.74o

Dilation and Variation of Friction Angle

0 = 13.9o

0 = 10.65o

0 = 9.7o

0 = 8.1o

Top Rings



15

30

45

14 15 16 17 18 19 20 21 220

15

30

45

14 15 16 17 18 19 20 21 22

3.37m 4m

4.65m 5.17m

Time [s]

0 = 9.23o

0 = 7o

0 = 8.1o

0 = 7.7o

Dilation and Variation of Friction Angle

0 = 7.35o

0 = 7o

0 = 6.4o

0 = 6.4o

Bottom Rings



15

30

45

0 2 4 6 8 10 120

15

30

45

2 4 6 8 10 12

0.78m 1.3m

1.94m 2.71m

Strain [%]

Friction Angle Vs Strain

Top Rings



15

30

45

0 2 4 6 8 10 120

15

30

45

2 4 6 8 10 12

3.38m 4m

4.65m 5.17m

Strain [%]

Friction Angle Vs Strain

Bottom Rings


Modified Newmark Rigid Modified Newmark Rigid Sliding Block AnalysisSliding Block Analysis

Coupled with Strength Coupled with Strength Degradation and variable yield Degradation and variable yield

accelerationacceleration


Model DescriptionModel Description

Original Laminar Box

Rings

Soil

a1(t)

a2(t)

ai(t)

an(t)

an-1(t)

Rigid Blockaavg(t)

• Weight of Rings, including the unfilled incorporated• Weight of each ring 11% of the weight of saturated soil filled in one ring• Horizontal Ground surface considered

Acceleration of the rigid block = Average of accelerometers present above the sliding surface

Yield Acceleration


Other AssumptionsOther Assumptions

Strength & Yield Acceleration varying with strain (& time) Yield Acceleration obtained from shear strength during

sliding

ayield = (fA-Wsin)/M f() = (1-ru)’v0tan

f() = shear strength during sliding = Friction angle varying with Strain (& time) A = Area of Laminar Box (12.75 m2), M = mass of the rigid

block

tatata yieldavgrel

t

rel ddatd0

1

0

22

1


Newmark Displacements Newmark Displacements [Top Rings][Top Rings]

10

20

30

40

50

14 16 18 20 220

10

20

30

40

50

16 18 20 22

0.78m 1.3m

1.94m 2.71m

Time [s]

Ho

rizo

nta

l Dis

pla

cem

en

t [cm

]

ShapeArray24 Initiation 1 Initiation 2

MODIFIED NEWMARK RIGID SLIDING BLOCK ANALYSIS

Excellent Agreement with Shape Array Data


Newmark Displacements Newmark Displacements [Bottom Rings][Bottom Rings]

10

20

30

40

50

14 16 18 20 220

10

20

30

40

50

16 18 20 22

3.37m 4m

4.65m 5.17m

Time [s]

Ho

rizo

nta

l Dis

pla

cem

en

t [cm

]

ShapeArray24 Initiation 1 Initiation 2

MODIFIED NEWMARK RIGID SLIDING BLOCK ANALYSIS


Threshold Flow Slide Strains & TimesThreshold Flow Slide Strains & Times

14 16 18 20 22

0

1

2

3

4

5

6

Time [s]

De

pth

[m]

0.25 0.5 0.75 1Strain [%]

Initiation 1Initiation 2

Time int

Top Rings slide at 19.29s Bottom Rings at 20.2s

Initiation 2 (Red)Threshold Strains between 0.4 to 0.65%


Excess Pore Pressure ResponseExcess Pore Pressure Response

0 10 20 30 40 50

0

1

2

3

4

5

6

Average Pore Pressure Profile

Excess Pore Pressure [kPa]

De

pth

[m]

t = 19st = 20st = 21st = 22st = 22.5slimit

0 0.2 0.4 0.6 0.8 1

0

1

2

3

4

5

6

Average ru Profile

De

pth

[m]

ru

t = 19st = 20st = 21st = 22st = 22.5s

Soil is NOT at liquefied state when lateral spread begins at 19.3 and 20.2 s.


Flow Slide Threshold StrengthsFlow Slide Threshold Strengths

0 10 20 30 40 50

0

1

2

3

4

5

6

'v [kPa]

De

pth

[m]

0.2 0.4 0.6 0.8 1'

v/'

v0

2 4 6S

u

0.1 0.2 0.3S

u/'

v0

15 30 45 [deg]

Initial State State at Initiation 1 State at Initiation 2

'v

'v/'

v0 Su

Su/'

v0

≈ C

onst

ant !

!!


Threshold StrengthsThreshold Strengths

0 10 20 30 40 50

0

1

2

3

4

5

6

'v [kPa]

De

pth

[m]

0.2 0.4 0.6 0.8 1'

v/'

v0

2 4 6S

u

0.1 0.2 0.3S

u/'

v0

15 30 45 [deg]

Initial State State at Initiation 1 State at Initiation 2 State at 22.5 s

'v

'v/'

v0 Su

Su/'

v0

Undrained Shear strength approaching initial static shear stress !!!


Some Variations in Initiation PointSome Variations in Initiation Point(More to come later)(More to come later)

Shear Strain

Sh

ea

r S

tre

ss

Shear Strain

Sh

ea

r S

tre

ss

Higher Amplitude

Shear Strain

Sh

ea

r S

tre

ss

Steady State Strength ≠ Initial Static Shear

Shear Strain

Sh

ea

r S

tre

ss

Peak Strength ≈ Initial Static Shear


Factors Conducive for Lateral Factors Conducive for Lateral SpreadingSpreading

SG-1

Shear Strain

0

Cyclic

Flow Failure

Strain Accumulation


Sh

ear

Str

ess

Shear Strain

LG-0


Small Strain Accumulation

• No Static Shear• Very little Strain Accumulation• No Flow observed• Failure termed as Liquefaction

• Non-zero Static Shear• Strain Accumulation until curve hits the strength envelope• Large Flow thereafter and curve follows the envelope• Failure termed as Flow Failure


Triaxial Test Data Triaxial Test Data (no initial shear, Theva 2003)

• e=0.779 (Moist tamping) • e = 0.778 (MT)

• e=0.804 (MT)

Is this what is seen in SG-1?Is hydraulic fill creating meta-stable structure more prone to collapse?Is collapse potential higher if static shear is present (i.e occurs at higher densities)?


ConclusionsConclusions Soil does not have to fully liquefy for lateral spreading to begin. But soil must be degraded to a ‘threshold’ strength for lateral spreading to

begin. Lateral spread likely begins when the soil is sufficiently degraded and the

cyclic curve hits monotonic strength envelope Threshold spreading point depends on initial static shear, cyclic shear amplitude,

pore pressure generation and associated degradation of soil strength. Once lateral spreading begins, little or no cyclic component exist. ‘Effective’ soil

friction angle during spreading increases. Modified Newmark Analysis, coupled with strength degradation, traces the

measured lateral displacements well. Undrained strength ratio at threshold lateral spreading falls in a narrow range

of about 0.08 Does hydraulic fill method create soil structure prone to collapse?

structural engineering and earthquake simulation laboratory sg-1: lateral spreading – observations...

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