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Transcript of 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
Structural Engineering and Earthquake Simulation Laboratory3
Review of SG-1 TestReview of SG-1 Test
Structural Engineering and Earthquake Simulation Laboratory4
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
Structural Engineering and Earthquake Simulation Laboratory5
SG-1 Test ConfigurationSG-1 Test Configuration
Top View
Side View
Structural Engineering and Earthquake Simulation Laboratory6
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
Structural Engineering and Earthquake Simulation Laboratory7
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
Structural Engineering and Earthquake Simulation Laboratory8
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
Structural Engineering and Earthquake Simulation Laboratory9
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
Structural Engineering and Earthquake Simulation Laboratory10
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 [%
]
Structural Engineering and Earthquake Simulation Laboratory11
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
Structural Engineering and Earthquake Simulation Laboratory12
Lateral Spreading Lateral Spreading MechanismMechanism
Structural Engineering and Earthquake Simulation Laboratory13
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
Structural Engineering and Earthquake Simulation Laboratory14
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
Monotonic Strength Envelope
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
Structural Engineering and Earthquake Simulation Laboratory15
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)?
Structural Engineering and Earthquake Simulation Laboratory16
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
Monotonic Strength Envelope
Flow Begins !!!
Structural Engineering and Earthquake Simulation Laboratory17
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
Structural Engineering and Earthquake Simulation Laboratory18
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
Structural Engineering and Earthquake Simulation Laboratory19
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
Structural Engineering and Earthquake Simulation Laboratory20
Soil Response @ 1.3m - Soil Response @ 1.3m - AnimationAnimation
Structural Engineering and Earthquake Simulation Laboratory21
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
Structural Engineering and Earthquake Simulation Laboratory22
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
Structural Engineering and Earthquake Simulation Laboratory23
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
Soil Response & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory24
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
Soil Response & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory25
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 & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory26
Soil Response @ 4m - Soil Response @ 4m - AnimationAnimation
Structural Engineering and Earthquake Simulation Laboratory27
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
Soil Response & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory28
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
Soil Response & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory29
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
Soil Response & Spreading InitiationSoil Response & Spreading Initiation
Structural Engineering and Earthquake Simulation Laboratory30
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
=
Structural Engineering and Earthquake Simulation Laboratory31
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
Structural Engineering and Earthquake Simulation Laboratory32
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
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
Structural Engineering and Earthquake Simulation Laboratory33
Mobilized Friction Angle Mobilized Friction Angle [during sliding][during sliding]
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
Structural Engineering and Earthquake Simulation Laboratory34
Mobilized Friction Angle Mobilized Friction Angle [during sliding][during sliding]
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
Structural Engineering and Earthquake Simulation Laboratory35
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
Structural Engineering and Earthquake Simulation Laboratory36
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
Structural Engineering and Earthquake Simulation Laboratory37
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
Structural Engineering and Earthquake Simulation Laboratory38
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
Structural Engineering and Earthquake Simulation Laboratory39
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
Structural Engineering and Earthquake Simulation Laboratory40
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%
Structural Engineering and Earthquake Simulation Laboratory41
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.
Structural Engineering and Earthquake Simulation Laboratory42
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 !
!!
Structural Engineering and Earthquake Simulation Laboratory43
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 !!!
Structural Engineering and Earthquake Simulation Laboratory44
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
Structural Engineering and Earthquake Simulation Laboratory45
Factors Conducive for Lateral Factors Conducive for Lateral SpreadingSpreading
SG-1
Shear Strain
0
Cyclic
Flow Failure
Strain Accumulation
Monotonic Strength Envelope
Sh
ear
Str
ess
Shear Strain
LG-0
Monotonic Strength Envelope
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
Structural Engineering and Earthquake Simulation Laboratory46
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)?
Structural Engineering and Earthquake Simulation Laboratory47
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?