Disaster Mitigation Geotechnology 5, 6 · PDF fileDisaster Mitigation Geotechnology 5, 6 Reality check: Field observation and physical modelling . ... caisson quay wall with lightweight

Disaster Mitigation Geotechnology

5, 6

Reality check: Field observation and

physical modelling

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

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.

Examples of numerical analysis checked against

field observations

Takahama Wharf, Kobe Port (PIANC, 2001)

Pier-type quay wall:

What’s the difficulty?

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

(PIANC,

2001)

- 3-D interactions between structures (piles) and soil

3-D interactions

Plan view

2-D representation

750mm (1/50 scale)

‘Physically’ model problems in interest – often in reduced scales

Physical Modelling

Model of

gravity quay

wall

- 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）

- 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)?

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

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

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

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

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

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

Instrumentation

Sensors (SSK website)

ロードセル

受圧板

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.

Validation of numerical analysis

‘Class A’ prediction or

blind test – Sometimes

successful, but not in

many cases.

Example of embankment (50G) – Tobita et al. (2005)

Loose sand Dense sand

Shaken at approx. 170 Gal

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

Effects of density and stress on undrained stress-

strain behaviour (Verdugo, 1992)

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)

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

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

Air-foam treated lightweight soil

Slurry tank

Cement and air foam mixing plant

Placing with Tremie pile

Air foam

Dredging

Screening

Tremie pile

Air foam treated

Light weight Geo-Material

(LGM)

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

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

Earth pressure transducer

Pore water transducer

Caisson

Caisson

Coarse sand Dr=98%

Caisson

Caisson

Sand Dr=80%

Coarse sand Dr=98%

Lightweight Backfill

Sand Dr=80%

Caisson

Coarse sand Dr=98%

LGM

Sand Dr=80%

(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

(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)


(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)


(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)



: A cce le ra tion

: E a rth p ressure


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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

(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

)


(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

)



: A cce le ra tion

: E a rth p ressure


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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

(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

)


(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

)


(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

)



: A cce le ra tion

: E a rth p ressure


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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


: A cce le ra tion

: E a rth p ressure


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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


De

pth

(m

)

0

2

4

6

8

10

0 30 60 90 120 150


De

pth

(m

)

: Before

: After

: 5th cycle

(c) Case3

0

2

4

6

8

10

-300306090120


De

pth

(m

)

0

2

4

6

8

10

0 30 60 90 120 150


De

pth

(m

)

: Before

: After

: 5th cycle

Case1

Case2 Case3

200 Gal shaking

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)


: A cce le ra tion

: E a rth p ressure


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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)

Case1 Case2

Case3 Case5 inversed trapezoidal

100 + 200 + 300 Gal shaking

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


A C 0

A C 4

A C 3

A C 2

E P 2



－＋

－＋

＋

AC1

W ate r


g =11kN/m3

q u =120kP a


＋－

＋

＋－

Unit: m

（Model: ×1／50 m）

E P 3

W P 1

E P 1

HD 2HD 1

C a isson

g =22kN/m3


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

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

(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


(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


Case1： Without Light BF

Case2： With Light BF of 5 m

Case3： With Light BF of 10 m

friction coefficient m = 0.5

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.

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

Now let’s see an thrilling film – Norwegian quick clay

ｰ Land slide in Nara Pref.

Documents

Disaster Mitigation Geotechnology 5, 6 · PDF fileDisaster Mitigation Geotechnology 5, 6 Reality check: Field observation and physical modelling . ... caisson quay wall with lightweight