Buddhima IndraratnaProfessor of Civil, Mining & Environmental Engineering

Director, Centre for Geomechanics and Railway Engineering

Faculty of Engineering, University of Wollongong

Wollongong City, NSW 2522, Australia

RECENT ADVANCES IN THE APPLICATION OF VERTICAL DRAINS AND VACUUM PRELOADING IN SOFT SOIL

STABILISATION

Contents

• Introduction to PVDs and VP application

• Role of Smear zone (disturbed soil zone around the mandrel), its assessment and implications

• Effect of Vacuum Pressure propagation and variation with time (including vacuum removal &reapplication)

• Experimental Investigations

• Numerical Modelling and Case History Analysis

• Advances in Design and Practice Guides

Potential Benefits of Prefabricated Vertical Drains in Soft Potential Benefits of Prefabricated Vertical Drains in Soft Formation ClaysFormation Clays

Surcharge Fill

Vertical drains with surcharge

Surcharge fill only – no vertical drains

Time

Sett

lem

ent

Vertical drains with surcharge and vacuum preloading

Dep

th

Lateral displacement at toe

Embankment

Inward Inward movement due movement due

to VPto VP

Due to Due to PVDsPVDs

Installation of PVDsInstallation of PVDs

Drain anchors and Mandrel shapes

Principles of Vacuum Consolidation Via PVDs

C lay

V acuum pum pM em brane

S ucharge F ill

Periphera l trench

Im perv iousslurry w all

PVD s

Sand b lanket

C lay

Vacuum pum p

Sucharge F ill

D rain C ollector

Membrane less system (e.g. Beaudrain)

Membrane system (e.g. Menard)

Soft Foundation Stabilisation by Vacuum ConsolidationSoft Foundation Stabilisation by Vacuum Consolidation

Surcharge Fill Only(Anisotropic Load)

Vacuum Preloading with PVD(Isotropic Loading)

Risk of Slope failure is minimized by the use of Vacuum Preloading

Vertical Stress

Vertical Stress

No FailureSlip Surface

Site preparation for Membrane-type Vacuum Consolidation(Courtesy of Austress-Menard)

Drain InstallationDrain Installation

Horizontal drain Horizontal drain installationinstallation

Peripheral bentonite trenchPeripheral bentonite trench

Connection between horizontal Connection between horizontal drainage and vacuum pumpdrainage and vacuum pumpMembrane installationMembrane installation

Site preparation for Vacuum Consolidation-Membraneless(Courtesy, CeTeau)

Drain InstallationDrain Installation

Tube connectionTube connection

Tim e

-150

-75

0

75

150

Str

ess

/P

ress

ure

(kP

a)

Tim e

-150

-75

0

75

150

Str

ess

/P

ress

ure

(kP

a)

p (pre loading pressure)

p (pre loading pressure)

p0 (Vacuum pressure)

Tim e

-150

-75

0

75

150

Exc

ess

por

e pr

essu

re (

kPa

)

Tim e

-150

-75

0

75

150

Exc

ess

por

e pr

essu

re (

kPa

)

Tim e

-150

-75

0

75

150

Ve

rtic

al e

ffect

ive

st

ress

(kP

a)

Tim e

-150

-75

0

75

150

Ve

rtic

al e

ffect

ive

st

ress

(kP

a)

M axim um excess pore pressure

M axim um excess pore pressure

Principle of Vacuum Consolidation

Consolidation: (a) conventional surcharge loading; (b) idealised vacuum preloading (Indraratna et al. 2005c).

2 2

2 2

1( )h v

u u u uc c

r r r z t

Governing Equation

(a) Suction in the drain (240mm from bottom); b) surface settlement surface settlement associated with simulated vacuum loading and removal (Indraratna et al. 2004).

Effect of Vacuum Removal and Reloading on Effect of Vacuum Removal and Reloading on ConsolidationConsolidation

After some initial consolidation, putting

off the vacuum pump is not going to make the soil swell up again, but the rate of settlement is swiftly retarded. Pumps

may have to be switched off from time

to time to prevent over-heating.

Experimental Evaluation of PVD + VP systemExperimental Evaluation of PVD + VP system

Large-Scale, Radial Drainage Consolidometer at Uni. of Wollongong

PVDPVD

HoistHoist

PPTPPT

PPTPPT

PPTPPT

VPLVPL

550mm Diameter 550mm Diameter

1.2m Height1.2m Height

Installation of PVDs by the steel mandrel causes smear around the PVD

Constant Strain Mandrel Driving

Hydraulic Loading

d

k k'

R

vertical drainsmear zone

specimen

D = 45 cm

ds

l = 950 mm

L o a d

T1 T2

T4

T6T5

T3

impermeable

24 cm

24 cm

24 cm

23 cm

Pore water pressuretransducer

permeable

Settlement transducera)

Sand drain

b)

horizontal specimenvertical specimen

smear zone

PVD and smear zonePVD and smear zone

Locations of cored Locations of cored specimensspecimens

Assessment of the Extent of Smear Zone Assessment of the Extent of Smear Zone

(Indraratna & Redana, 1998, Sathananthan & Indraratna 2006)(Indraratna & Redana, 1998, Sathananthan & Indraratna 2006)

Drain

0 5 10 15 200

0.5

1

1.5

2

Radial distance, R (cm)

Smear zone

Band Flodrain

Mean Consolidation Pressure:6.5 kPa

16.5 kPa32.5 kPa64.5 kPa

129.5 kPa260 kPa

kk

hv

/

Permeability ApproachPermeability Approach

Indraratna & Redana, 1998, JGGE, ASCEIndraratna & Redana, 1998, JGGE, ASCE

Vol. 124(2)Vol. 124(2)

0 1 2 3 4 5r /rm

6 2

6 4

6 6

6 8

7 0

Wat

er c

onte

nt, w

(%

)

L o catio n o f th e s m ap lefro m b o tto m (m m )

0 (b o tto m )

2 0 0

4 0 0

6 0 0

8 0 0

Dra

in

S m ea r zo n e

w m a x = w s = 6 9 %

Water Content ApproachWater Content ApproachSathananthan & Indraratna 2006, JGGE, Sathananthan & Indraratna 2006, JGGE,

ASCE, ASCE, Vol. 132(7)Vol. 132(7)

Evaluation of Smear EffectsEvaluation of Smear Effects

Vacuum Propagation Model based on Laboratory Data

Vacuum pressure distribution patterns in the vertical and lateral directions (after Indraratna et al. 2005).

ks < kh

If k1 =1, there is no vaccum loss with depth

Lateral Propagation of VP

Soil element

Soil-drain interfaceCL

(a) Large-scale triaxial rig; (b) soil specimen (Indraratna et al. 2009a).

Cyclic Loading and Soil Consolidation via PVDsCyclic Loading and Soil Consolidation via PVDs

Cyclic Loading Actuator

Cyclic Excess Pore Pressure Response of Soft Clay With and Without PVD (Indraratna et al., 2009)(Indraratna et al., 2009)

Specimens without PVD fail very quickly as the

excess pore pressure rises rapidly!

0 1000 2000 3000 400 0N (C yc les )

0

0 .2

0 .4

0 .6

0 .8

1

Exc

ess

po

re p

ress

ure

ra

tio, u

*

0

0 .5

1

1 .5

Vo

lum

etr

ic s

tra

in, v

(%

)

0

10

20

30

Exc

ess

por

e p

ress

ure

, u

(kP

a)

C K oU , W ithou t P V D

T 6 , w ith P V D

T 3, w ith PV D

W ith P V D (com press ion )

(a)

(b)

U U ,W ithou t P V D

U ndra ined , w ithou t PV D

Failure of samples

T3

T6

FEM Simulation of Mandrel-driven PVD – Pore Pressure FEM Simulation of Mandrel-driven PVD – Pore Pressure CREATION due to very high plastic strainsCREATION due to very high plastic strains

Mandrel Driving INCREASES effective vertical stress, hence, the lateral permeability decreases within the smear zone (Indraratna et al. 2009, ASCE J. of Geomechanics).

1. Excess Pore Pressure is rapidly created during mandrel intrusion

2. Excess PWP dissipates very gradually after mandrel withdrawal in spite of the drain.

1 0

2 0

3 0

u (

kPa)

2 0 k P aT 1

T 2

T 3

T 4

T 5

1 0

2 0

3 0

u (k

Pa)

3 0 k P aT 1

T 2

T 3

T 4

T 5

1 0

2 0

3 0

4 0

u (k

Pa)

4 0 k P aT 1

T 2

T 3

T 4

T 5

0 1 0 0 2 0 0 3 0 0T im e E lap sed (sec)

0

2 0

4 0

6 0

Por

e P

ress

ure,

u (

kPa) 5 0 k P a

T 1

T 2

T 3

T 4

T 5

Pore pressure variation during mandrel installationPore pressure variation during mandrel installation

Locations of pore pressure transducersLocations of pore pressure transducers

1=

1=

1=

1=

T im e

Por

e w

ater

pre

ssur

e

Z o n e a

Z o n e b

Z o n e c

Z o n e d

Z o n e a : B efo re m a n d re l p en e tra tio nZ o n e b : P o re p ressu re in c re ase a s th e m an d re l a pp ro a ch es th e lo c a tio n o f p o re p re ssu re tra n sd u cerZ o n e c : M a n d re l p asses th e lo ca tio n o f tran sd uc erZ o n e d : M an d re l w ith d raw al

Mandrel

T1

T2

T3

T4

T5

Analytical and Numerical Simulation Analytical and Numerical Simulation Multi-drain Analysis and Plane Strain Conversion

Field condition: Axisymmetric

Reduce the convergence time and require less computer memory

Must give the same consolidation response

Maintain geometric equivalence

2D plane strain FEM

Conversion of an Axisymmetric Unit Cell into Plane Strain Conversion of an Axisymmetric Unit Cell into Plane Strain

Indraratna et al., 2000 & 2005 Indraratna et al., 2000 & 2005

Conversion must Conversion must give the give the SAMESAME time- time-

settlement curvesettlement curve

w

h

wp

hp

qkl

shkhk

sn

q

k

Bl

hpkhpk

hk

hpk

32

75.0lnln

34

2

2

No conversion (some published work)

After conversion

0.1 1 10 100 1000T im e (days)

0

0.2

0.4

0 .6

0 .8

1A

vera

ge

exc

ess

po

re p

ress

ure

ra

tio

c h=0.32m 2/yeard e=0.45m

A xisym m etric

P lane stra in

0.1 1 10 100 1000T im e (days)

0

0.2

0.4

0 .6

0 .8

1A

vera

ge

exc

ess

po

re p

ress

ure

ra

tio

ch=0.32m 2/yearde=0.45m

Axisym m etric

P lane strain

2 graphs co inc ide

0

vach

o

vac

o u

uT8exp

u

u1

u

u

Normalized average excess pore pressure in axisymmetric condition with vacuum (Indraratna et al., 2005), CGJ

= pore pressure at time t (average values)

= time factor

= undisturbed horizontal permeability

= smear zone permeability

0u = initial pore pressure

u

hT

w

h

h

h

q

kls

k

k

s

n

3

275.0)ln(

'ln

2

hk

h'k

vacu = average applied vacuum pressurekh

ks

-p0

-k1p0

z

l

ds/2

de/2

Smear zone

Undisturbed zone

Vacuum pressure distribution

CL

Degree of Consolidation: Pore pressure Based Models (Indraratna et al. 2008)

Surcharge alone

Vacuum alone

Vacuum + Surcharge alone

D epth

Effective stress

u 0=hww hww + h fillf i llu t

U t

u 0+(f ill)

D epth

Effective stress

u 0=h wwu t

U tSuction line (u s)

VP(fill)

u 0+(f ill)

D epth

Effective stress

u 0=h ww

u t

U t

Suction line (u s)

VP

hww -V P

t

fillfill

tfillfillwwp

u

h

uhhU

VP

u

VP

uhU ttww

p

VP

u

VPh

uhhU t

fillfill

tfillfillwwp

Case Study 1: Port of Brisbane Ground Improvement

Dredging for Reclamation fill PVD installation

Vacuum stabilised areaMarine boundary and sandy platform

Essential Design Aspects (selected section)

W D 5A W D 5BW D 1

V C 2

W D4

W D 2 W D3

VC 1

155m

35m

70m 41m 84.5m 84.5m

70m

70m

50m

169m

210m

M S 15-1

M S17-1 M S 18-1

M S16-1M S22-1 W D 5B

VC 1-2

VC 2-1

Surface settlem ent p la tes

P iezom eters

VW P2-W D 1

V W P1-W D 2

VW P4-W D 4

M S 20-VW P5

M S19-VW P5

M S 28-VC 1

M S 27-W D 3

Inclinom eters

0 40 80

L iqu id and p lastic lim it (% )

-30

-20

-10

0

10

Ele

vatio

n (m

)

PL

LL

W ater Content

0.4 0.6 0.8 1

C c

2 4 6 8C v, C h (m 2/yr)

C h

C v

20 40 60 80S u (kP a)

D redged m ud

U pper H o locene sand

H olocene C lay

P le is tocene

Plan view Soil Properties

Service load @ 25 kPa, Max. residual settlement@ 250 mm over 20 yrs.

Sea wall and future

development area

Time-Settlement and Pore Pressure Response

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

14/0

5/0

7

11/0

6/0

7

09/0

7/0

7

06/0

8/0

7

03/0

9/0

7

01/1

0/0

7

29/1

0/0

7

26/1

1/0

7

24/1

2/0

7

21/0

1/0

8

18/0

2/0

8

17/0

3/0

8

14/0

4/0

8

12/0

5/0

8

09/0

6/0

8

07/0

7/0

8

04/0

8/0

8

01/0

9/0

8

29/0

9/0

8

27/1

0/0

8

Sett

lem

en

t (m

)

Prediction

Field

UOW Predicted DOC (%)

0

20

40

60

80

100

14/05/07 22/08/07 30/11/07 09/03/08 17/06/08 25/09/08

Degre

e o

f C

onsolid

atio

n

(%)

-10

0

10

20

30

40

50

60

70

14/05/07 22/08/07 30/11/07 09/03/08 17/06/08 25/09/08

Exc

ess

po

re p

ress

ure

(kP

a)

MudSandClaySoft ClayField Measurement

(a) Settlement and (b) excess pore pressure for non-vacuum site

Higher k promotes greater PWP dissipation

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

11/0

5/07

08/0

6/07

06/0

7/07

03/0

8/07

31/0

8/07

28/0

9/07

26/1

0/07

23/1

1/07

21/1

2/07

18/0

1/08

15/0

2/08

14/0

3/08

11/0

4/08

09/0

5/08

06/0

6/08

04/0

7/08

01/0

8/08

29/0

8/08

26/0

9/08

24/1

0/08

21/1

1/08

Set

tlem

ent

(m)

Prediction

Field

UOW Predicted DOC (%)

0

10

20

30

40

50

60

70

80

90

100

11/05/07 19/08/07 27/11/07 06/03/08 14/06/08 22/09/08

De

gre

e o

f C

on

so

lid

ati

on

(%

)

-80

-60

-40

-20

0

20

40

60

11/05/07 19/08/07 27/11/07 06/03/08 14/06/08 22/09/08

Exc

ess

pore

pre

ssur

e (k

Pa)

Dredged MudUpper Holocene SandUpper Holocene ClayLower Holocene ClayMeasurement

More than doubled settlement obtained with VP at the same time scale

(a) Settlement and (b) excess pore pressure for a typical vacuum site

Effect of OCR and clay thickness on residual settlementLateral Displacement reduction due to vacuum application

Reduction in lateral movement due to VP

Case Study (2): Trial Embankment Stabilized with PVD and Vacuum Preloading, Ballina Bypass, Australia

Typical soil properties

8 12 16D ensity (kN /m 3)

20

10

0

De

pth

(m

)

D ry density

W et density

40 80 120

M oisture content (% )

In-s itu

L iqu id lim it

P lastic lim it

0 .32 0.36 0.4

C c/(1+e 0)

0 .04 0.08 0.12

C r/(1+e 0)

40 60 80

p c '

0 10 20 30 40 50

U ndra ined shear strength (kPa)

Soft S ilty C lay

M edium S ilty C lay

Instrumentation layout

No vacuumVacuum

Test Embankment Cross Section

-70 kPa vacuum and max. 8 m surcharge applied at this site

S o ft S ilty C lay

M ed iu m S ilty C lay

S= 1m , 3 4 m m d iam eter c ircu la r d ra in s w ith a squ a re p a tte rn

B e n to n ite tre n c h

S an d G eo m em b ran e P u m p

2 0 mC L

S u rfac e se ttle m e n t p la te

In c lin o m e te r

P ie z o m e te rs

Dep

th (m

)

Performance : soil properties before and after vacuum application

The void ratio, compressibility Index and water content decrease significantly in the initial 17m. Beyond that, only a marginal decrease is observed.

PVD+VP system is mainly effective at the upper regions of the clay.

Performance: Lateral displacement

• Lateral movement decreases due to vacuum, even at higher fill heights.

• Ratio of lateral movement to fill height is a better indicator of the stability provided by VP

No VacuumNo Vacuum

Case Study (3): Test Embankment Stabilized with PVD and Vacuum

Preloading in Soft Bangkok Clay, Thailand (Indraratna et al 2005, Int. J. of Geomechanics, ASCE, 114-124)

-60 kPa design vacuum and max. 2.5 m surcharge

W e a th e re d c la y

V e ry so ft c la y

S o ft c lay

M ed iu m c la y

S tiff to h a rd c la y

S= 1 m , l= 1 5 m , T rian g u la r p a tte rn

B e n to n ite tre n c h

S a n d G eo m em b ra ne P erfo ra ted p ip eP u m p

2 0 mC L

+ 2 .5

+ 0 .80 .0

-2 .0

-8 .5

-1 0 .5

-1 2 .0

-1 3 .0

-1 5 .0

S u b -su rfac e se ttle m e n t p la te an de le c tica l p ie z o m e te r

L e g e n d

In c lin o m e te r

1 5 m

D u m m y a re a(re fe ren c e p o in t)

O b se rv a tio n w e lls a n ds ta n d p ip e p ie z o m e te rs

Dep

th (m

)

Vacuum Simulation (selected section)(Indraratna and Redana, 2000)

Model A: Conventional analysis (no vacuum; only surcharge fill)

Model B: Vacuum pressure is adjusted according to field measurement and reduces linearly to zero at the bottom of the drain (k1= 0)

Model C: Perfect seal (vacuum pressure was kept constant at -60kPa after 40 days); vacuum pressure varies linearly to zero along the drain length (k1= 0)

Model D: No vacuum loss along the drain length (k1=1)

Field measurementsField measurements

Model C: Assumed VP

0 4 0 8 0 1 2 0 1 6 0Tim e (D ays)

-8 0

-6 0

-4 0

-2 0

0

Vac

uum

pre

ssur

e (k

Pa

)

Excess pore pressure

Surcharge OnlySurcharge Only

0 4 0 8 0 1 2 0 1 6 0T im e (D ays)

-8 0

-6 0

-4 0

-2 0

0

2 0E

xces

s po

re w

ater

pre

ssur

e (k

Pa

)

F ie ld m e asu rem e n t M o d e l A

M o d e l B

M o d e l C

M o d e l D

0 4 0 8 0 1 2 0 1 6 0T im e (D ays)

-1 .6

-1 .2

-0 .8

-0 .4

0

Set

tlem

ent (

m)

F ie ld m e asu rem en t M o del A

M o de l B

M o de l C

M o de l D

Settlement

Lateral Movements at Embankment Toe

Key Advantages:

Surcharge fill height reduced from 4.0m to 2.5 m

Time for 95% consolidation reduced from 12 months to 4 months.

Weathered Crust is much Weathered Crust is much stiffer in reality than the stiffer in reality than the assumed properties assumed properties

3D vacuum pressure propagation across the boundaries of treated zone

Effect of vacuum application (negative movements) may extend

more than 10 m from the edge of the embankment

A

A

Lateral movement

A

x

y

A A

0

1 2

3

4 56 78 9 1011

12

1314

15

1617

18

1920

21

2223

24

25

26

51

52

5366

67

68

Case Study 4: Railway Applications: FEM Analysis of Short PVDs at Sandgate

Class A Prediction (Indraratna et al, ASCE, JGGE, 2010)

Very Soft AlluvialVery Soft Alluvial Clay Clay

Soft Silty ClaySoft Silty Clay

0 100 200 300 400 500Tim e (days)

0

20

40

60

80

Exc

ess

pore

pre

ssu

re (

kPa

) No PVD

W ith PVDs @ 1.5m spacing

0 0.1 0.2 0.3Latera l d isp lacm ent (S h,m )

-20

-16

-12

-8

-4

0

De

pth

(m

)

N o PVD

W ith PVD s @ 1.5m spacing

R eduction in la tera l d isp lacem ent

Rapid dissipation of excess pore pressure Curtailing lateral displacement

CONCLUSIONSCONCLUSIONS

Vacuum preloading rapidly decreases excess pore pressure, and directly increases effective stress with time. Conventional surcharge models simulate the increase in total stress, and associated increase in the excess pore pressure.

Smear effects adversely affect PWP dissipation, and the application of VP and corresponding increase in the hydraulic gradient partially compensates for this.

PVDs in combination with vacuum and surcharge fill curtail lateral movements and provide stability for the superstructure. Excessive VP generates high inward movement causing tensile zones.

Sophisticated 3-D numerical modelling is not required if appropriate conversion to 2D plane strain can be made for most sites for multi-drain analysis. Exceptions would be marine boundaries and corners.

Field monitoring for VP sites is essential to ensure performance, and to establish any time-dependent variation of VP distribution.

CONCLUSIONSCONCLUSIONS Vacuum preloading rapidly decreases excess pore pressure, and

directly increases effective stress with time. Conventional surcharge models simulate the increase in total stress, and associated increase in the excess pore pressure.

Smear effects adversely affect PWP dissipation, and the application of VP and corresponding increase in the hydraulic gradient partially compensates for this.

PVDs in combination with vacuum and surcharge fill curtail lateral movements and provide stability for the superstructure. Excessive VP generates high inward movement causing tensile zones.

Sophisticated 3-D numerical modelling is not required if appropriate conversion to 2D plane strain can be made for most sites for multi-drain analysis. Exceptions would be marine boundaries and corners.

Field monitoring for VP sites is essential to ensure performance, and to establish any time-dependent variation of VP distribution.

AcknowledgementAcknowledgement

Australian Geomechanics Society (AGS)

Dr Geng Xueyu and Dr Cholachat Rujikiatkamjorn during compiling and editing of a vast amount of data from the past 15 years of research in vertical drains and vacuum preloading conducted at University of Wollongong (UOW).

More than a dozen past and present research students who have contributed to the contents of this lecture directly and indirectly.

Australian Research Council – Linkage and Discovery project funding

Research Collaborations with many Industry Partners and Institutions over the years: Queensland Department of Main Roads, Port of Brisbane Corporation, Roads & Traffic Authority, Coffey Geotechnics, Asian Institute of Technology, Thailand; Polyfabrics, Geofabrics, ARUP, Douglas Partners, Snowy Mountains Engineering Corporation, RailCorp, ARTC, Chemstab, Queensland Rail and Austress-Menard

Technical staff, University of Wollongong

Thank YouThank You

Practicing Engineers’ Dilemma - Disparity between Excess Pore Pressure and Settlement

Indraratna, Balasubramaniam & Ratnayake, Journal of Geotechnical Engineering, ASCE, Vol. 120, No. 2, pp. 257-273, 1994..

Settlements may continue to occur, when excess pore pressure is still not dissipated.

Solution: Increase hydraulic Gradient towards drains by applying vacuum pressure

Rate of excess pore pressure dissipation influenced by:

(a) high visco-plastic strains

(b) clogging of drains

(c) malfunctioning piezometer tips

Sudden high rainfall

0 100 200 300 400Tim e (d a ys)

0

20

40

60

80

100

Lo

ad

(kP

a)

0 100 200 300 400Tim e (d a ys)

1 .6

1 .2

0 .8

0 .4

0

Se

ttle

me

nt (

m)

0 100 200 300 400Tim e (d a ys)

0

40

80

120

160

Exc

ess

po

re p

ress

ure

(kP

a)

S tag e c o n stru c tio n

S ettle m en t

E x c ess p o re p ressu re

Settlement close to the embankment centreline

0 40 80 120 160 200Tim e (s)

5

10

15

20

5

10

15

20

5

10

15

20

5

10

15

20

25

M easured

FE M

Exc

ess

por

e p

ress

ure

(kP

a)

T1

T2

T3

T4

Predicted and measured pore pressure during vertical drain

installation

Extent of the smear zone based on permeability

measurement and finite element prediction

0 1 2 3 4 5r/rm

0

2

4

6

Soi

l per

mea

bilit

y (x

10-1

0 m

/s)

0 .4

0 .8

1 .2

1 .6

u/p

0

M easured

FEM

rs/rm =2.5

PW

P/in

itial

tota

l st

ress

Applications (4): 3D FEM Application: Land Reclamation Stabilized with PVD and Vacuum Preloading Tianjin port ,

China (Rujikiatkamjorn, Indraratna and Chu 2008, Int. J. of Geomechanics, ASCE)

Soil Profile

0 20 40 60Atte rberg lim its (% )

25

20

15

10

5

0

De

pth

(m

)

Plastic lim it

W ater conten t

L iqu id lim it

20 40 60 80

V ane S hear S trength (kPa)

0.4 0.8 1.2 1.6 2Void ra tio Soil

descrip tion

S ilty c lay(taken from sea bed)

M uddy clay

So ft s ilty c lay

S tiff s ilty c lay

Embankment Plan View & Instrumentation

Soil Profile, Embankment Cross Section & Instrumentation

1 5 m 1 0 m

P erfo ra ted P ip e M e m b ra n e

P refab rica ted V ertica l D ra in S = 1 .0 0 m in sq u a re p a tte rn

3 .5 m .

0 .3 m

0 .0 m

-4 .5 m

-7 .0 m

-2 0 m

-1 0 .5 m

V acuum P u m p

M ulti-leve l gauge

Pore water transducer

Inclinom eter

CL

Piezom eter

-1 4 .5 m

-1 6 .5 m

yz

Embankment Cross Section

N

30m

80m 119m

S ettlem ent gauge

P ore w ater transducer

F ie ld vane

Inclinom eter

P iezom eter

M ulti-level gauge

Section I Section II

A

A

Section III

50m

27.9m

x

y

x

y

Settlement Predictions

Soil parameters

Depth(m)

e0

s

kN/m3

kv10-10 m/s

kh,ax10-10 m/s

k’h,ax10-10 m/s

kh,ps10-10 m/s

k’h,ps10-10 m/s

OCR

0.0-3.50.12

0.03

0.3 1.1 18.3 6.67 20 6.67 5.91 1.461-1.1

3.5-8.50.14

0.03

0.25

1.0 18.8 13.3 40 13.3 11.8 2.921.2-1.5

8.5-16.0

0.20

0.04

0.31.35

17.5 6.67 20 6.67 5.91 1.461.2-1.6

16.0-20.0

0.10

0.02

0.27

0.9 18.5 1.67 5 1.67 1.48 0.3651.1-1.4

0 40 80 120 160 200T im e (days)

1.6

1.2

0.8

0.4

Set

tlem

ent

(m)

0

40

80

120

160

Pre

load

pre

ssu

re (

kPa)

F ie ld

2D FE M (R ujik ia tkam jorn et a l. 2007)

3D FEM

Vacuum pressure under m em brane

Vacuum plus pre loading

(a)

(b)

Surface

3.8m

7.0m

10.5m

14.5m

D epth

3D FEM mesh

x

z

y

14m25m

20m

20m

20m

20m

0

x=0 p lane

y=0 p lane

14m 20m

y

z

0

2D FEM mesh (converted)

Surface Settlement Predictions

Soil parameters

Finite element analysis: Vertical settlement

2009 E H DAVIS LECTURE Buddhima Indraratna