experimental verification of shallow foundation
TRANSCRIPT
Experimental Verification
of Shallow Foundation Performance
under Earthquake-Induced Liquefaction
National Technical University of Athens Foundation Engineering Laboratory
Karamitros Dimitris (N.T.U.A., Greece)
Cilingir Ulas (U.Cam., U.K.)
Bouckovalas George (N.T.U.A., Greece)
Madabhushi Gopal (U.Cam., U.K.)
Papadimitriou Achilleas (U.Th., Greece)
Haigh Stuart (U.Cam., U.K.)
Seismic Engineering Research Infrastructures for European Synergies
Concluding Workshop - Joint with US-NEES:
“Earthquake Engineering Research Infrastructures” JRC-Ispra, May 28-30, 2013, in memory of Prof. Roy Severn
Cambridge University Technical Services
Niigata, Japan (1964)
M=7.5
Caracas, Venezuela (1967)
M=6.5
Liquefaction Performance of Shallow Foundations
in Recent Earthquakes
Luzon, Philippines (1990)
M=7.8
Chi-Chi, Taiwan (1999)
M=7.3
Liquefaction Performance of Shallow Foundations
in Recent Earthquakes
Kocaeli (Izmit)
Turkey (1999)
M=7.8
Liquefaction Performance of Shallow Foundations
in Recent Earthquakes
non-liquefiable
surface "crust"
liquefiable
soil
H
Zliq
D
0 2 4 6 8 10
H / D
0
2
4
6
8
10
Zli
q / D
D=
1m
D=
3m
Failure (D=1m)
Failure (D>3m)
Non-failure
Acacio et al (2001)
Data from Dagupan (1990)
Modified curves after Ishihara (1985)
Can a sufficiently thick and shear resistant non-liquefiable crust
ensure the viable performance-based design of shallow foundations?
Karamitros et al (2013)
Fully-Coupled Effective-Stress Analyses
Liquefiable Sand: Dr=40,50,60%
Clay Cap: Cu=25,40kPa
tied-node boundary conditions
B=5m
q=40,70,100,140kPa
H=2,4,6m
Z=6,11,16,21m
60m
73 parametric analyses
for strip foundations (2D)
N=5,10,20amax=0.05, 0.10, 0.15, 0.25, 0.35g
T=0.25, 0.35, 0.50sec
at
18 parametric analyses
for square foundations (3D)
Liquefiable Sand: D r=50%
Clay: cu=25, 40kPa
15m
50m
H=
2,4
,6m
Z=
5.2
5,1
0.5
0,1
5.7
5m
p'
q
Dilatancy Surface
Critical State Surface
Bounding Surface
Yield Surface(vanished)
r3 r2
r1
r
rIP
rLR
NTUA-Sand constitutive model…
…implemented into FLAC & FLAC3d (U.D.M.)
Calibrated against laboratory tests for Nevada Sand
Verified against centrifuge tests (incl. VELACS #12)
Square footing (3D)
c=0.008
Strip footing (2D)
c=0.035
0 0.2 0.4 0.6 0.8 1 1.2
1 / FSdeg
0
0.01
0.02
0.03
0.04
ρd
yn / [
(am
ax T
2 N
) (Z
liq / B
)1.5
]
31.5
liq2dyn max
deg
Z 1c a T N
B FS
Seismic Settlements
Meyerhof & Hanna (1978):
u cs
ult ,deg
u s q qs
2 c F
q min H 12c s H BN F HN F
B 2
functions of φ
Cascone &
Bouckovalas (1998)
φ → φdeg
degtan 1 U tan
Post-shaking Degraded Bearing Capacity
Clay cap
Liquefied Sand
qult,deg
B
H
cu,γ'
φ,γ',U
0.00
10.
01 0.1 1
0.00
2
0.00
50.
020.
05 0.2
0.5 2
ρdyn (m) - experimental
0.001
0.01
0.1
1
0.002
0.005
0.02
0.05
0.2
0.5
2
ρd
yn (
m)
- a
na
lyti
ca
l50
%
200%
Dynamic Settlements (Centrifuge & Shaking-table Tests):
Yoshimi & Tokimatsu (1977)
Liu & Dobry (1997)
Kawasaki et al (1998)
Acacio et al (2001)
Adalier et al (2003)
Coelho et al (2004)
38 experiments
Verification Against Experimental Data
Post-shaking degraded bearing capacity: no experimental data
Centrifuge Model Configuration
Test
1
Test
2
Test
3
H = 2.0m 3.0m 5.0m
Zliq = 14.5m 13.5m 11.5m
Kaolin Clay (Grade E)
Leighton-Buzzard Sand(Fraction E)
Square FootingB=3m , q = 94 kPa
HydraulicActuator
Load Cell
Accelerometer
P.P.T.
L.V.D.T.MEMS Accelerometer
Potentiometer
H
Zliq
0 Load (Q)0
Dis
pla
ce
me
nt
(ρ)a
b
d'd
c
static lo
adin
g
to fa
ilure
Test Procedure
Each test consisted of 3 steps:
Static loading (spin-up phase)
Seismic loading applied using S.A.M. actuator
Post-shaking loading applied by the hydraulic piston
ρst
ρd
yn
Qultdeg
Experimental Facilities
Philip Turner
Centrifuge
(Schofield Centre)
Radius = 4.125m
Capacity = 150g
Tests performed at 50g
Stored Angular Momentum
S.A.M. Actuator
amax = 0.25g (up to 0.4g)
T = 1.0sec (0.2÷1.0sec)
N = 20cylces (up to 100)
Equivalent Shear Beam
E.S.B. Box
Inside plan area: 673mm ×253mm
33.6m × 16.5m prototype, at 50g (sealed by spraying with synthetic plastic coating)
Dry Sand Pluviation
Robotic apparatus for uniform sand deposition
Leighton-Buzzard Sand (Fraction E)
Instrumentation Placement
Accelerometers PPTs
Model Saturation
Safety pressure release valve CO2 flushing
de-aired water – methylcellulose
mixture (viscosity = 50cSt)
vacuum applied through
computer-controlled
pressure regulator
for automatic control
of the saturation process
Clay Crust Preparation
1 10 100 1000
Applied Pressure (KPa)
220
230
240
250
260
270
280
Cla
y T
hic
kn
es
s (
mm
)
σ'v=80kPa
σ'v,max=400kPa
over-consolidated
Grade-E Kaolin Clay
Centrifuge Model
hydraulic actuator
pressure switch
L.V.D.T.s load cell footing web-cam
junction & power boxes Model Footing
Standpipe for excess pore water dissipation
Typical Results: Accelerations
5 10 15 20 25 30 35 40
time (sec)
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
ac
ce
lera
tio
n (
g)
5 10 15 20 25 30 35 40
time (sec)
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
ac
ce
lera
tio
n (
g)
5 10 15 20 25 30 35 40
time (sec)
-1.5
-1
-0.5
0
0.5
1
1.5
ac
ce
lera
tio
n (
g)
Typical Results: Excess Pore Pressure Ratios
5 10 15 20 25 30 35 40
time (sec)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
r u =
Δu
/ σ
' v,o
5 10 15 20 25 30 35 40
time (sec)
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
r u =
Δu
/ σ
' v,o
Typical Results: Settlements
5 10 15 20 25 30 35 40
time (sec)
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
0.1
se
ttle
me
nt
(m)
New Evidence:
Post-Shaking Loading
0 10 20 30 40 50 60 70 80 90 100
time (sec)
-100
0
100
200
300
400
500
600
700
q (
kP
a)
0 10 20 30 40 50 60 70 80 90 100
time (sec)
-1
-0.5
0
0.5
1
r u =
Δu
/ σ
' v,o
0 10 20 30 40 50 60 70 80 90 100
time (sec)
-2.5
-2
-1.5
-1
-0.5
0
0.5
se
ttle
me
nt
(m)
0.7
165kPa
Effect of Clay Crust on Dynamic Settlements
0.1 10.2 0.3 0.5 2
ρdyn (m) - analytical predictions
0.1
1
0.2
0.3
0.5
ρd
yn (
m)
- e
xp
eri
me
nta
l re
su
lts
+50%
-50%
0.5 1 1.5 2
H / B
0.1
1
0.2
0.3
0.5
ρd
yn (
m)
- e
xp
eri
me
nta
l re
su
lts
cu=32kPa
cu=21kPa
cu=32kPa
cu=21kPa
cu=32kPacu=32kPa
(H/B)cr = 1.54
B
H
B
H'
Subsoil liquefaction
does not affect foundation performance
in general: (ρdyn/B)cr<1%
Thank you for your attention!