Download - Hybrid Drain Geosynthetics for fine-grain soil improvements

Hybrid Drain Geosynthetics for fine-grain soil improvements

Chandan GhoshProf. & Head [Geohazards]

National Inst. of Disaster ManagementMinistry of Home Affairs, Govt. of India

PWP-3

PWP-2

PWP-1

H

CONSOLIDATION PRESSURE (P=20,50,100,200,400 KPA)

DR

AIN

FA

CE

U

150MM DIAMETER

Kanto loam slurry

Drain layer

Large strain slurry consolidation

• Do slurry behave similar to normal soil?• Do PWP in slurry different from normal

Terzaghi soil?• Can internal PWP be measured?• Do k, Cv, Cc, mv are constant with

consolidation pressure?• Permeability –direct and from Consolidation

theory differ much?

3

Typical application/troubles!! 様々な工法や問題

Important!!!Drain flow capacity

Local soils being excavated to construct road

Prepared foundation base

(a)

(b)Permeable high strengthgeocomposite

Rains

Imposed load

Geocomposite drain/reinforcement Details "b"

Drained water dueto consolidation

Settlement

Traffic load

Soft soil

In-plane flow

Problem domain

Local/problematic soils

Load types

Drain/reinforcement

Time dep. Sett.?

Clogging…flow capacity changes under confinement

Geosynthetics as drain

• Drain – clogging and efficiency in flow under pressure

• In-plane and x-plane flow be measured?• Index properties of geosynthetics• International codal practice• Evaluation of clogging – from slurry stage• Drain efficiency – hybrid drain system

6

AIM of present research

To recommend suitable drain system for field application

To assess nature of clogging and flow capacity of drains confined in fine-grained soil

7

Research needs

Flow capacity of synthetic drains placed in-situ

Assessment of clogging and its prevention

Recommending design flow capacity of drains based on available hydraulic index test data

Use of synthetic materials for improving fine-grained soils

8

Geosynthetics used

Geocomposite-AGC-A

Nonwoven –ANW-A

Nonwoven –BNW-B

Nonwoven –CNW-C

Nonwoven cover

Woven fabric

0

20

40

60

80

100

0 10 20 30 40 50 60 70 80

Elongation (%)

Tens

ile lo

ad (k

N/m

)

Nonwoven -A (EX-60)

Nonwoven-B (EX-80)Geocomposite-B (RD-15)

Geocomposite-A (RD-40)

Geocomposite-C (RD-80)In-air Tension test Width = 50mmGage length=100mmStrain rate = 20%/minTest done as per JIS L 1908

9

Grain size distribution

0

20

40

60

80

100

0.001 0.01 0.1 1 10 100Grain size (mm)

Perc

ent f

iner

(%)

Toyoura sand

Silty clay Kanto loam

Imposed load


drained water dueto consolidation

Settlement

In-plane flow

X-plane flow

10

Clogging mechanism

tg

Clogged particles

Piped particles

Randomly oriented geotextile fibres

Interface

Blinding

Woven-nonwoven type geocomposite

Woven fabricParticle deposition

Fine-grained soilswater flow with fines

Geosynthetic clogged by Kanto loam

Consolidation of soil – ideal vs natural

• Can we measure excess PWP directly?• Can excess PWP exceeds applied load increment?• What if load increment ratio varies from 0.5 to 3?• What if applied pressure is increased in steps or

in one go - say from p=0 to 400kPa?• How Excess PWP varies with H or with r?• How different is “k” – if measured in a

large specimen?

AIM

• what happens inside slurry when loaded upto 400kPa

• How different are all parameters?• Drained water and settlement – how are

they related?• To check soil bevaviour and looking into

gap – theory and practice

Leh cloud burst - 2010

• Slurry formation• Mud slides• Prevention of mud slides

• Measuring in-plane flow and drain efficiency using a large dia consolidation apparatus

• Measuring internal PWP during test• Validation of consolidation theory

NEW BUS STAND

SONAM NORBOO MEMORIAL HOSPITAL

BSNL OFFICE

HIGHLY POPULATED COMMERCIAL AREA

Cloud burst at Leh, 4-5 Aug 2010Boundary Wall of DIHAR Broken by slurry

16

Apparatus developed



(a)


Rains

Imposed load



Settlement

Traffic load

Soft soil

In-plane flow

Basis of developingexperimental methods

coarse sand

LVDT

Air pressure chamberPlexiglasscylinder

O-ring

150mm 350mmSoil slurry

20 channel data logger

Weightbalance

Weightbalance

Porous stone affixed withflexible tube

PWP-1 PWP-3

3.15flexible tube

Data cable

Air pressure vent

PWP-2

Geosyntheticdrain layer

17

Test procedure

PWP-3

PWP-2

PWP-1

Data logger

Airpressure regulator

Silty claysample

Setting PWP tipsCompacting sand base Geocomposite

as boundary drain filter

Silty clay slurry

Blinding of Geocomposite filter

Particle blinding

(a) (c)(b) (d)

(f)

(g)(e)

Silty clay

220 mm150mm

18

Flow tests in drains placed within Kanto loam and silty clay

during consolidation

Soil slurry

Drain (120x50mm)

Consolidation pressure

Drain pipe

Kanto loam slurry

Drain layer

19



(a)


Rains

Imposed load



Settlement

Traffic load

Soft soil

In-plane flow

Various in-plane flow tests carried at in-situTest situation – double layer drain system

Double layer drain and in-situ state

Geocomposite-AGC-A

Nonwoven –ANW-A

Nonwoven –BNW-B

Nonwoven –CNW-C

2.7mm thick4mm thick 5.5mm thick 6.2mm thick

20

Various drains tested in-situ during consolidation of slurry

Water flow in Flow out

Soil slurrySand

Perspex cylinder wall

Sectional plan 120mmX50mm drain sample

PWP device

Conso. pressure

Multilayer drain system

120mmPorous stone tip

Hybrid drains

(a) Basic sample - BA

(b) Horiz. sand drain - HSD

(c) Geocomposite drain - GCA

(d) GCA+HSD = HB1

(e) GCA+HSD = HB2

(f) GCA+HSD = HB3

150mm

100

GCA

HB1

HB3

HB2

NWA

HSD

NWB

NWC

Toyoura sand

21

Status of drains after test

(a) Geocomposite drain susceptible to clogging

KL-GC drain

(b) HYBRID drain less susceptible to clogging

KL-HB2

(c) Geocomposite drain susceptible to clogging (d) HYBRID drain less susceptible to clogging

CS-GC drain CS-HB2

Clogging by Kanto loam Almost no clogging due to sand mat

Thin sand mat used in HYBRID drain

120mm

50mm

Clogged geocomposite drain sampleplaced within silty clay

Nearly clean geocomposite drain found after test in HYBRID system

22

Permeability factor – in-situ

0

5

10

15

20

25

10 100 1000Consolidation pressure (kPa)

Perm

eabi

lity

k x

10-9

(m/s

) Silty clayKanto loam

k-values by water flow test

k-values from consolidation test

0

5

10

15

20

10 100 1000Consolidation pressure (kPa)

Perm

eabi

lity

fact

or x

105 =

k-G

C d

rain

/k-s

oils

Kanto loamSilty clay

Flow factor w.r.t. no clog GC drain

Flow factor w.r.t. clog GC drain

In-situ state

Permeability factor = ‘k’-no clog drain/’k’- soil1. Permeability factor >105, which is satisfactory2. With increasing pressure this factor increases, which is also a good indication

23

Flow tests in drains placed within Kanto loam and silty clay

during consolidation

Soil slurry

Drain (120x50mm)

Consolidation pressure

Drain pipe

Kanto loam slurry

Drain layer

24

Average in-plane flow capacity 平均水平流動量

0

0.05

0.1

0.15

0.2

0.25

0.3

10 100 1000Consolidation pressure, (kPa)

Tran

smiss

ivity

x 1

0-5,

(m2/

s)

Silty clay

No clog GC

(b)

Hybrid-2

0

0.05

0.1

0.15

0.2

0.25

0.3

10 100 1000Consolidation pressure, (kPa)

Tran

smis

sivi

ty x

10-5

, (m

2 /s)

No clog GCHSDGCDHB1HB2HB3

Kanto loamNo clog GC

(a)

0

1

2

3

4

5

10 100 1000

Consolidation pressure p, (kPa)

Ave

rage

flow

rate

q (m

l/min

)Hyd. Grad. i=1

Silty clay

(b)

Hybrid -2

0

1

2

3

4

5

10 100 1000

Consolidation pressure p, (kPa)

Ave

rage

flow

rate

q (m

l/min

) NWANWBNWCHB2

Hyd. Grad. i=1

Kanto loam

(a)

Soil

Drain

Consolidationpressure

In-situ state

1. Flow in HYBRID drain is the highest2. Without sand mat flow is the low, NWC drain is the lowest3. Confining pressure causes 70 to 80% reduction in GC drain

Clogging of drains

• How to evaluate clogging?• How to remove clogging of drains? –

ultrasonic removal• Hybrid drains – combination of geotextile

and sand mat

26

Clogging of geocomposite

Inner woven part

Kanto loamSilty clay

Nonwoven cover

Large dia – 1D consolidation

• Can PWP be measured directly?• Slurry and normal soil states – at 50 kPa• Variation of internal excess PWP – with height ?• Do excess PWP attains 100% immediately after

applied pressure?• Direct and indirect permeability – are they same?• k, p, mv, Cc, Cv – are these constant with p?• Can we measure Drained water during

consolidation?

Consolidation from slurry stage

• Kanto loam – slurry (is there a relation between LL and slurry water content?)

• Why p=50 kPa?- transition from slurry to Terzaghi soil

Kanto loam slurry

Drain layer

At p=400kPa (dia =150mm, H=57mm)

0 5 10 15 20 250

20

40

60

80

100

120

140 PWP-2PWP-3PWP-4

Time, hrs

PWP,

kPa

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

0.25

0.5

0.75

10.10 hrs0.281.55.511.521.55

PWP ratio, u/del p

Sam

ple

heig

ht, z

/H

Kanto loam – local soil and silty clay - commercial

Material Kanto loam (local soil)

Silty clay (commercial)

Plasticity LL % 108.1 37.7 PL % 82.3 16.4 PI 25.8 21.3Natural water content (%) 101 3

Particle density, s (Mg/m3) 2.687 2.612

d max (kN/m3) 7.66 11.96Optimum w% 82 17Initial void ratio of slurry 6.70-8.00 2.30-3.30

Grain size –Clay, Silt, Sand 10%, 27%, 63% 43%, 55%, 2%

Triaxial (UU), uu, cuu 40, 19.6 kN/m2 - - -

(CU), cu, ccu 250, 5.9 kN/m2 - - -

0 100 200 300

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Kanto loamSILTY CLAY

Time (hrs)

Verti

cal s

trai

n

0.01 0.1 1 10 100 1000 10000

0.00

0.03

0.06

0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2

p=400 kPa

(e)

0.01 0.1 1 10 100 1000 100000.00

0.03

0.06

0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2

p=200 kPa

(d)

0.01 0.1 1 10 100 1000 100000.00

0.03

0.06

0.09 0.0 0.2 0.4 0.6 0.8 1.0 1.2

p=100 kPa

(c)

0.0 1 0. 1 1 10 10 0 1 00 0 10 00 00. 0 0

0. 0 5 0. 1 0

0. 1 5 0. 2 0 0.0

0.2 0.4 0.6 0.8 1.0 1.2

p= 5 0 k P a

(b )

15 0m m di am e ter

P WP-3P WP-2P WP-1

H

C on so li da ti on p res su re , p

Drain

face

u

0.01 0.1 1 10 100 1000 100000.00 0.10 0.20 0.30 0.40 0.50 0.0

0.2 0.4 0.6 0.8 1.0 1.2 Vertical strain vs time

PWP-2 at mid height vs time

Consolidation time, min

p=20 kPa

Kanto loam (a)

Exce

ss p

ore

wat

er p

ress

ure

ratio

(u/d

el

p)

Verti

cal s

train

of s

lurr

y sa

mpl

e

t50 at p=400kPa

0 5 10 15 20 25 30 35 40 4587

89

91

93

95 400 T50,T10...

Sqrt. T(min)

t50=55mint100=264min

Is there a unique transitional stage at p=50kPa?

1 10 100 10000

50

100

150

200

250

Si lt y clayKan to lo am

Consol id ation pr essur e, k Pa

Slurr

y he

ight,

mm

H5 0=57m m

H50 =110m m

H50=23m m

No rm al soi l s tat e

Slur r y s tat e

P WP- 3

P WP- 2P WP- 1

H50

Co n so li da tio n p res su re (p = 50 k P a)

Drain

face

u

1 50 m m di am e te r

1 10 100 10000.0

0.5

1.0

1.5

2.0

2.5

0

20

40

60

80

100 110mm thick at 50 kPaSeries357mm thick at 50 kPa

Consolidation pressure, kPa

Void

ratio

, e0-

e

Indi

cativ

e w

ater

cont

ent (

%)

Silty clayLL=37.7%PL=16.4%

Oeodometer specimen (60mm dia, 20mm height)

(a)

CcS=1.1

Normal soil stateSlurry state

Water content = 37%

CcN=0.31

1 10 100 10000

2

4

6

8

0

50

100

150

200

250

300 110mm thick t 50 kPaoedo-KL57mm thick at 50 kPa


Void

ratio

, e0-

e

Indi

cativ

e w

ater

cont

ent (

%)

Kanto loamLL=108%PL=82%

Oedometer specimen(60mm dia, 20mm height)

(b)

CcN=1.1

CcS=3.1

Slurry state Normal soil state

Water content = 124%

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0


Voi

d ra

tio (e

at p

=1 to

400

kPa

)/e

at p

=1 k

Pa)

Normal soilSlurry

Std. Oedometer specimen(60mm dia, H=20mm)

Silty clay slurry150 mm dia for

H50=23mm, 56mm, 110mm

(a)

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0


Voi

d ra

tio (e

at p

=1 to

400

kPa

)/e

at p

=1 k

Pa)

Normal soilSlurry

Std. Oedometer specimen(60mm dia, H=20mm)

Kanto loam slurry150 mm dia with

H50=23mm, 56mm, 110mm

(b)

mv, Cv, k – are not constant

0 100 200 300 4000.0

2.0

4.0

6.0

8.0

10.0

0

2

4

6

8

10

12k-indirectk-direct

Consolidation pressure p, kPa

Perm

eabi

lity

k, m

/sX1

e-9

"k"

dire

ct X

1e-

6

10 100 10000.0

0.2

0.4

0.6

0.8

1.0

0

2

4

6


mv(

p)/m

v(p=

20 k

Pa) a

nd

k(p)

/k(p

=20k

Pa)

Coeff

. of c

onso

lidati

on, m

2/yr

cv vs p (Oedometer)

cv vs p

mv ratio vs p

k ratio vs p

10 100 10000.0

0.2

0.4

0.6

0.8

1.0

0

2

4

6


mv

(p)/

mv

(p=2

0 kP

a) a

nd

k(p)

/k(p

=20

kPa)

Coeff

. of c

onso

lidati

on, m

2/yr

cv vs p (Oedometer)

cv vs p mv ratio vs p

k ratio vs p

With more “p”, u/p reduces

0 25 50 75 100 125 150 175 200 225 250 275 3000

0.2

0.4

0.6

0.8

1

Kanto loam

Silty clay

Time (hrs)

Exce

ss P

WP

ratio

, u/p

Excess PWP (p=20 to 400kPa)

0 20 40 60 80 100 120 140 160 180 2000

20

40

60

80

100

120

1400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

PWP-2, kPaPWP-3PWP-4

Cons. Time, hrs

Exc

ess P

WP,

kPa

Ver

tical

stra

in

Clay sand basic 100 mm

0 0.5 1 1.50.00

0.25

0.50

0.75

1.00

0.05 hrs0.23351.3168333335.79016666711.7901666723.79016667

PWP u/D p

z/H5

0

p=20 kPa

0 0.5 1 1.50.00

0.25

0.50

0.75

1.00

0.03hrs0.1951666670.57855.04516666711.9951666725.99516667

PWP ratio, u/D p

z/H5

0

p=50 kPa

PWP-3

PWP-2

PWP-1

PWP-3PWP-2PWP-1 H

50

Consolidation pressure (p=50 kPa)

Dra

in fa

ce

u

150mm diameter

PWP inside specimen

0 0.5 1 1.50.00

0.25

0.50

0.75

1.00

0.02hrs0.23350.6501666674.95016666711.9501666725.95016667

PWP ratio, u/Dp

z/H5

0

p=100 kPa

0 0.5 1 1.50.00

0.25

0.50

0.75

1.00

0.05hrs0.23350.6501666671.4501666676.95016666725.95016667

PWP ratio, u/D p

z/H5

0

p=200 kPa

0 0 .5 1 1.50.0 0

0.2 5

0.5 0

0.7 5

1.0 0

0.10 hrs

0.281.55.511 .521 .5 5 01 66 67

P WP r atio , u /D p

z/H5

0

p= 400kP a

PWP-3

PWP-2

PWP-1

PWP-3PWP-2PWP-1

H 5 0

Co nsol i dat i on pr essure ( p=50 kPa)

Dra

in fa

ce

u150m m diam eter

PWP-3PWP-2PWP-1 H

50

Consolidation pressure (p=50 kPa)

Dra

in fa

ce

u

150mm diameter

Excess PWP is more than net increase in “p”

10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

PWP-3PWP-2PWP-1


Peak

exc

ess P

WP

ratio

, u/p

Silty clay

u/Dp

u/p

(a)

10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Consol ida tion pr essur e p, kPa

Peak

exce

ss PW

P ra

tio

Kanto l oam

u/Dp

u/p

(b)

15 0 mm di am e ter

P WP -3P WP -2P WP -1 H

Co n so li da ti on p re ssu r e, p

Drain

face

u

Permeability - direct

0 50 100 150 200 250 300 350 4000

500

1000

1500

0

1

2

3

4

5

t50 vs pClay sand t50 vs p Cv vs pclaysand Cv vs p

p, kPa

t50,

min

Coeff

. con

solid

ation

, m2/

yr

sample100 mm

0 50 100 150 200 250 300 3500

1

2

3

4

5

6

p=50 kPa 100

200 400

Flow pressure, u (top) kPa

Dire

ct P

erm

eabi

lity,

k (m

/s)X

exp

-9

Kanto Loam

0 50 100 150 200 250 300 3500

0.5

1

1.5

2

2.5

3

3.5

4

4.5p=50 kPa 100 200400

Flow pressure, u (top) kPa

Perm

eabi

lity,

k (m

/s)X

exp

-9

Silty clay

1 10 100 1000 100000

1

10

100

1000

5010020040020

Consolidation time, min

Darc

y pe

rmea

bilit

y x1

0-9,

m/s

Kanto loam

e – p curve

0 100 200 300 400 500 600 7000

2

4

6

8


void

ratio

, e Kanto loamCc=1.1Cc (Cal)=0.8 Silty clay

Cc=0.31Cc(cal)=0.25

Oedometer sample

11010010002.0

2.5

3.0

3.5

4.0

50 100

200 400

Darcy permeability x 10-9, m/s

Void

ratio

chan

ge, e

Kanto loam

55

New developments　New multi-purpose test apparatus developed

– Flow capacity at in-situ state & increasing confinement

– Excess pore water measurement inside specimen

– Direct measure of ‘k”, vertical strain, drained water

Conclusions• Transition between slurry and normal Terzaghi soil

state occurred at consolidation pressure of 50 kPa. • Water content at this transition state found fairly

close to the respective liquid limits of the Kanto loam and silty clay.

• Peak excess PWP represents the state at which soil undergoes maximum rate of compression.

• ‘e-log p’ curves for slurry state and normal soil state are different and it has two separate Cc values.

Thank you

Download - Hybrid Drain Geosynthetics for fine-grain soil improvements

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