Disaster Mitigation Geotechnology 5, 6 · PDF fileDisaster Mitigation Geotechnology 5, 6...
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Disaster Mitigation Geotechnology
5, 6
Reality check: Field observation and
physical modelling
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Particular problem given
(slope, retaining wall, etc.)
Performance evaluation: evaluation system
Typical flow
Prediction of performance
Simple
pseudo-
static
analysis
Newmark’s
method
Dynamic
numerical
analysis
Physical
modelling
Field
observations
Empirical
charts
L1 L2
Research
behind design
codes
Validation
Derivation
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Why cannot numerical analysis alone be enough?
- Imperfect constitutive modelling
Unrealistic stress-strain relationships
- Imperfect boundary value problem modelling
Some problems are difficult to model perfectly
(complex geometry, etc.)
- Imperfect implementation of numerical analysis
Particularly difficult for large strain problems; why?
These are in addition to uncertainty in the ground conditions
(for which numerical analysis itself is not to be blamed!)
Check against reality needed.
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Examples of numerical analysis checked against
field observations
Takahama Wharf, Kobe Port (PIANC, 2001)
Pier-type quay wall:
What’s the difficulty?
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Examples of numerical analysis checked against
field observations
(PIANC,
2001)
- 3-D interactions between structures (piles) and soil
(friction, drag, etc.)
- Relative strength of soil layers
- Properties of backfill soil
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(PIANC,
2001)
- 3-D interactions between structures (piles) and soil
3-D interactions
Plan view
2-D representation
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750mm (1/50 scale)
‘Physically’ model problems in interest – often in reduced scales
Physical Modelling
Model of
gravity quay
wall
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- Conditions well controlled
(Geotechnical, hydraulic, structural, loading conditions)
- Instrumented
(Measuring loads, pressures, accelerations, displacements, etc.
at desired locations)
- Mechanisms observed; useful for large deformation problems
- Ease of construction in reduced scales
Advantages of physical modelling
Punching-through of spudcan
foundation
(Hossain and Randolph, 2010)
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- Comparatively expensive and labour-intensive
- It is not a copy of real phenomena; only idealisation
(e.g. normally laboratory-prepared soil is used instead of natural
soils)
- Some physical limitations exist – A problem of similitude (相似則)
Disadvantages / limitations of physical modelling
Scaling law of physical quantities between real
scale (prototype scale) and model scale
e.g. Let us assume we make a 1/50-scale model.
What should the input acceleration be?
Same as the prototype (say, 400 Gal for L2)?
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Example of bearing capacity problem on clay
Problem of similitude
v h
uS
Stress and undrained
shear strength profiles
Plasticity solution (when Su is constant across depth):
Bearing capacity, q, even though it is a ‘per-area’ quantity, is under-
estimated due to reduced stress level in reduced scales.
q : Bearing capacity
uSq 14.5
Prototype
½ model
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Example of bearing capacity problem on clay
Solution – Centrifuge testing
v h
uS
Stress and undrained
shear strength profiles
Increase the stress level by centrifuge acceleration:
1G 2G in this case (i.e. similitude for acceleration)
q : Bearing capacity
Prototype
½ model
v h
uS
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How to apply centrifugal acceleration?
– Geotechnical centrifuge
- Arm (beam) type
- Drum type
@ Port and Airport Research Institute
Effective radius of 3.8m
@ Hokkaido University
Effective radius of 1.5m
2 rc r
: Radius
: Angular velocity
c
g
r
Model
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Similitude in centrifuge test
Noting the dimensions of quantities,
scaling factors are derived. Physical
quantities
Model /
Prototype
Length 1/n
Acceleration n
Mass 1
Force 1/n2
Stress 1
Strain 1
Displacement 1/n
Time 1/n
Frequency n
Velocity 1
If there existed heavy soil particles
whose properties are identical to
real soils, what would they be?
Simulating seismic acceleration
of A [Gal] in centrifuge requires
nA [Gal] (but amplitude reduced by
1/n)
In-flight shaking table
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Consolidation in centrifuge
Consolidation theory:
If length is 1/n, consolidation
progresses n2 times faster.
(same for seepage)
Physical
quantities
Model /
Prototype
Length 1/n
Acceleration n
Mass 1
Force 1/n2
Stress 1
Strain 1
Displacement 1/n
Time 1/n
Frequency n
Velocity 1
Contradiction here:
To correct for this, fluid with larger
(n-times larger than that of water)
viscosity is used as pore water.
Important in simulation of
liquefaction
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Physical limitation: an example
Think of levee;
To keep the Reynolds number Re = UL/n :
Viscosity needs to be 1/n times the reality :
To keep the seepage/consolidation time:
Viscosity needs to be n times the reality
Dynamics of fluid:
Reynolds number ,etc.
Seepage
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Instrumentation
Sensors (SSK website)
ロードセル
受圧板
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Shaking in centrifuge (50G)
Shaking
0 100 200 300 4000.0
0.1
0.2
0.3
Light Caisson
No DM grid
Half-depth DM grid
Full-depth DM grid
Heavy caisson
No DM grid
Half-depth DM grid
Full-depth DM grid
Settle
ment at to
e (
Pro
toty
pe s
cale
) [m
]
Base acceleration (prototype scale) [Gal]
Example shown in photos
Mechanism clearly seen.
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Validation of numerical analysis
‘Class A’ prediction or
blind test – Sometimes
successful, but not in
many cases.
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Example of embankment (50G) – Tobita et al. (2005)
Loose sand Dense sand
Shaken at approx. 170 Gal
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1-G (gravity field) physical model tests
Behaviour of stress-dependent materials such as soil
cannot be reproduced under 1G.
If it is to be done, a care is required:
For example, for liquefaction problem:
- Looser sand than reality
See next slide
- Faster shaking (i.e. higher frequency)
To achieve undrained conditions
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Effects of density and stress on undrained stress-
strain behaviour (Verdugo, 1992)
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Examples of 1G physical model tests
Subsidence of embankment (Mizutani, 2001)
Liquefaction of quay wall backfill (Towhata, 2008)
Physical models are also used
to evaluate effectiveness of
countermeasures (discussed in
later weeks)
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Overall Summery of Anti-Seismic Geotechnical Design
- Anti-seismic design concept has undergone changes:
Specification-based Performance-based
- We need to know what performance we need of
individual geotechnical structures
- Analytical methods exist at varying degree of
sophistication and complexity. All of them (even very
simple ones) are used widely in practice.
- Field observations and physical modelling are an
integrated part of ant-seismic design; on their own, or
as means to validate analysis
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Seismic performance of
caisson quay wall with lightweight backfill
Yoichi Watabe Port and Airport Research Institute
Shinichiro Imamura Nishimatsu Construction Co., Ltd.
Takashi Tsuchida Hiroshima University
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Air-foam treated lightweight soil
Slurry tank
Cement and air foam mixing plant
Placing with Tremie pile
Air foam
Dredging
Screening
Tremie pile
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Air foam treated
Light weight Geo-Material
(LGM)
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WUpper
(m) WLower
(m) H (m)
Shaking (Gal) 2Hz, 20 cycles
Case 1 0 0 0 100, 200 & 300
Case 2 5 5 5 100, 200 & 300
Case 3 10 10 5 100, 200 & 300
Case 4 10 10 5 300
Case 5 10 5 5 100, 200 & 300
Backfill sand
Substratum
CCaaiissssoonn
Lightweight soil
: 5 m (prototype) / 100 mm (model)
WLower
H
10 m
7 m WUpper
Centrifuge model
shaking test at 50g
Rectangle
Inversed trapezoid
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Substratum(Silica sand)Dr = 98%
Lightweight backfill
g = 11 kN/m3,qu = 120 kPa
Water
Unit: m
(Model: ×1/50 m)
+ +
AC1
+ -
AC2
+ -
AC3+ -
AC4+ -
AC02 Hz(Model 100 Hz)
20 cycles100, 200, 300 Gal
EP2
Caisson
g = 22 kN/m3
Backfill (Toyoura sand)
Dr = 80%
WP1
HD1 HD2
EP1
-50
50
150
250
-30 70 170 270 370 470 570
12.5
2.5
82
5
5 7
Case 1: 0 mCase 2: 5 mCase 3: 10 mCase 4: 10 mCase 5: 5 m (lower); 10 m (upper)
303.5 3.5
2.5 for Cases 1, 2 & 55.0 for Cases 3 & 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
Horizontal displacement Earth Pressure
Water Pressure Acceleration
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Earth pressure transducer
Pore water transducer
Caisson
Caisson
Coarse sand Dr=98%
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Caisson
Caisson
Sand Dr=80%
Coarse sand Dr=98%
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Lightweight Backfill
Sand Dr=80%
Caisson
Coarse sand Dr=98%
LGM
Sand Dr=80%
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(a ) A C 0
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: C ase1 : C ase2 : C ase3
: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
200 Gal shaking
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(b ) A C 1
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: C as e1 : C as e2 : C as e3
(c ) A C 2
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: C as e1 : C as e2 : C as e3
(d ) A C 3
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: C as e1 : C as e2 : C as e3
(e ) A C 4
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: C as e1 : C as e2 : C as e3
: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
200 Gal shaking
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(f) HD 1
-0 .04
0 .00
0 .04
0 .08
0 .12
0 .16
0 .20
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ho
rizo
nta
l d
isp
lac
em
en
t (m
)
: C as e1 : C as e2 : C as e3
(g ) HD 2
-0 .04
0 .00
0 .04
0 .08
0 .12
0 .16
0 .20
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ho
rizo
nta
l d
isp
lac
em
en
t (m
)
: C as e1 : C as e2 : C as e3
: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
200 Gal shaking
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(h) W P 1
0
20
40
60
80
100
120
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Wa
ter
pre
ss
ure
(k
Pa
)
: C as e1 : C as e2 : C as e3
(i) E P 1
0
10
20
30
40
50
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ea
rth
pre
ss
ure
(k
Pa
)
: C as e1 : C as e2 : C as e3
(j) E P 2
0
20
40
60
80
100
120
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ea
rth
pre
ss
ure
(k
Pa
)
: C as e1 : C as e2 : C as e3
: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
200 Gal shaking
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: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
(a) Case1
0
2
4
6
8
10
-300306090120
W ater pressure (kPa)
Dept
h (
m)
0
2
4
6
8
10
0 30 60 90 120 150
Earth pressure (kPa)
De
pth
(m
)
: Before
: After: 5th cycle
(b) Case2
0
2
4
6
8
10
-300306090120
W ater pressure (kPa)
De
pth
(m
)
0
2
4
6
8
10
0 30 60 90 120 150
Earth pressure (kPa)
De
pth
(m
)
: Before
: After
: 5th cycle
(c) Case3
0
2
4
6
8
10
-300306090120
W ater pressure (kPa)
De
pth
(m
)
0
2
4
6
8
10
0 30 60 90 120 150
Earth pressure (kPa)
De
pth
(m
)
: Before
: After
: 5th cycle
Case1
Case2 Case3
200 Gal shaking
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0.0
0.1
0.2
0.3
0.4
0.5
0 100 200 300 400
入力加速度 (G al)
ケーソンの水平変位増分
(m
) : C A-1
: C A-2
: C A-3
: C A-4
Input acceleration (Gal)
0 100 200 300 400
0.5
0.4
0.3
0.2
0.1
0.0
Case 1
Case 2
Case 3
Case 4
Case 5
Incr
emen
tal h
oriz
onta
l dis
plac
emen
t
at e
ach
stag
ed s
haki
ng (
m)
: Ho rizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
Incre
menta
l horizonta
l
dis
pla
cem
ent
at each s
taged s
hakin
g
(m)
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Case1 Case2
Case3 Case5 inversed trapezoidal
100 + 200 + 300 Gal shaking
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M o d e l b o x
fro n t
M o d e l b o x
b a c k
C a is s o n
fro n t
(a b s o lu te ly )
C a is s o n
b a c k
(a b s o lu te ly )
C a is s o n
fro n t
(re la t ive ly )
C a is s o n
b a c k
(re la t ive ly )
C ase2
-600
-400
-200
0
200
400
600
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Ac
ce
lera
tio
n (
Ga
l)
: A C 0 (a ) : A C 2 (b ) : (b ) - (a )
: Horizonta l d isp lacem ent
: A cce le ra tion
: E a rth p ressure
: W a te r p ressure
A C 0
A C 4
A C 3
A C 2
E P 2
2Hz(Model 100Hz)20cycles
100, 200, 300GalInput acce le ra tion
-+
-+
+
AC1
W ate r
L ightwe ight backfi ll
g =11kN/m3
q u =120kP a
Substratum(Silica sand)Dr=98%
+ -
+
+ -
Unit: m
(Model: ×1/50 m)
E P 3
W P 1
E P 1
HD 2HD 1
C a isson
g =22kN/m3
B ackfi ll (Toyoura sand )
D r=80%
-50
50
150
250
-30 70 170 270 370 470 570
12
.5
2.5
82
5
5 7
Case1: 0m
Case2: 5m
Case3: 10m
Case4: 10m
303.5 3.5
2.5 for C as e1& 2
5 for C as e3& 4
2.4
11
2.6
53
4.3
5 13
1
1.2
5
200 Gal shaking
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C ase2
-800
-400
0
400
800
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Fo
rce
(k
N)
: Ine rtia (C a isson) : E a rth p ressure (a )
: W a te r p ressure (b ) : (a )+(b )
200 Gal shaking
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(a )C ase1
200G a l
B ac k →F ron t
(re la t ive ly )
-1000
-500
0
500
1000
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Fo
rce
(k
N)
: S lid ing fo rce
: F ric tion res is tance
(b )C ase2
200G a l
B a c k →F ro n t
(re la t ive ly )
-1000
-500
0
500
1000
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Fo
rce
(k
N)
: S lid ing fo rce
: F ric tion res is tance
(c )C ase3
200G a l
B a c k→F ro n t
( re la tive ly)
-1000
-500
0
500
1000
0 .00 0 .25 0 .50 0 .75 1 .00 1 .25 1 .50
Tim e (sec)
Fo
rce
(k
N)
: S lid ing fo rce
: F ric tion res is tance
Case1: Without Light BF
Case2: With Light BF of 5 m
Case3: With Light BF of 10 m
friction coefficient m = 0.5
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CONCLUSIONS
In the case with sand backfill, active failure in the
backfilled sand occurred, while in the cases with
lightweight backfill, two independent active failures
occurred in the sand behind the lightweight backfill and
the caisson.
Horizontal displacement of the caisson during
earthquake was significantly decreased by lightweight
backfill.
The effect of the inversed trapezoidal lightweight backfill
to decrease the horizontal displacement is much higher
than that of the rectangular lightweight backfills.
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No.1,No.3
1 : 2
–15.50
–7.80
H.W.L. +1.70
L.W.L. +0.00 –1.00
+1.80
+4.20
32.4m
裏埋土砂
盛砂
裏込石
基礎捨石
置換砂粘性土 粘性土
気泡混合処理土R.W.L. 0.6m
ケーソン
12.4m
22.8m
No.2
印:サンプリング位置
S.C.P.改良土
No.1,No.3
1 : 2
–15.50
–7.80
H.W.L. +1.70
L.W.L. +0.00 –1.00
+1.80
+4.20
32.4m
裏埋土砂
盛砂
裏込石
基礎捨石
置換砂粘性土 粘性土
気泡混合処理土R.W.L. 0.6m
ケーソン
12.4m
22.8m
No.2
印:サンプリング位置印:サンプリング位置
S.C.P.改良土
: Sampling points
(No.1—3)
Lightweight soil
Caisson
Rubble
Backfill
(stones)
Sand
Compaction
Piles Sand fill
Sand mound
Displaced sandClay Clay
H.W.L. +1.70 m
L.W.L. +0.00 m
–15.50 m
+4.20 m
+1.80 m
–1.00 m
–7.80 m
32.4 m
12.4 m22.8 m
R.W.L. +0.6 m
Kobe Port Island Restoration work after
Kobe Earthquake in 1995
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Now let’s see an thrilling film – Norwegian quick clay
ー Land slide in Nara Pref.