International Geosynthetics SocietyIGS Education Committee

Training Course on Geosynthetics8IGG, Yokohama, 2006

Geosynthetics in Drainage and Filtration

Prof. J.P. GourcUniversity of Grenoble, France

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Geosynthetics in Drainage and Filtration

Prof. J.P. GourcUniversity of Grenoble, France

International Geosynthetics SocietyIGS Education Committee

Training Course on Geosynthetics 8IGG, Yokohama, 2006

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Hydraulic functions of geosynthetics

-1- Separation

-3- Drainage

-2- Filter

Container

2

33

Woven Geotextiles

Woven

Examples ofPermeable basic Geotextilesfor hydraulic applications

Non-Woven

monofilament

Slit-film

Needle-punched

44

--11--SeparationSeparation

-First application of geotextiles (before 1970)

-To prevent mixing of two soils , due to mechanicalsolicitations

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55

66

RoadsRoadsRailwayRailway

Parking area,…Parking area,…

Applications ofGeosynthetics for Separation

4

77

88Highway embankment

5

99

To avoid such a difficult situation !

1010

geotextiles are used to prevent road base materials from penetrating into soft underlying soft subgrade, thus maintaining design thickness and roadway integrity

geotextile separators also prevent fine-grained subgrade soils from being pumped into permeable, granular road bases

geotextile

6

1111

1212

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1313

Separation function is nota clearly independant function:

-Solicitation isn’t only mechanicalbut also hydraulic

-Separation function is correlated to reinforcement & filtration functions

1414

Punching of the Soft soil

FillSettlement

Embankment on very soft soilEmbankment on very soft soil

Geosynthetic

(Tensile mobilization)

8

1515

Embankment on soft soil

(Northern Canada)

1616

subsoil

subgrade

ballast

Geotextile

Railway

Geotextile (risk of abrasion)

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1717

Pollution Pollution ofof thethe ballast layer,ballast layer,due to due to pumpingpumping

ofof fine fine particlesparticles ofof thethe subsoilsubsoil

1818

10

1919

2020

--22--FiltrationFiltration

( Complex phenomenon ! )

-To prevent the instability of soil

subjected to hydrodynamic stresses

-To mobilize a low passive resistance

to water flow in the same time ,

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2121

Filtration with geosynthetics

Filter Application – Trench Drain

Without filtration(pipe clogging)

2222

Trench with geosynthetic filter

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2323

French drain

2424

Requirements for an Efficient Filter

• To be permeable enough

• To NOT retain the fines particles (in a first step)

• To Retain the soil

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2525

Design Criteria for Geosynthetic Filters

. Soil Retention ( to prevent piping)

. Permeability (to insure adequate flow)

. Long Term Effectiveness ( to prevent clogging)

. Survivability-Durability (to prevent damaging during installation)

2626

Filtration function:

Mechanism of retention

To promote equilibrium of particles

after limited washout of finer particles

by inducing a self-filtration zone (bridging)

at the interface (Lafleur,1989).

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2727

Mechanism of Retention:-Retain largest (upstream)particles first

-Retain by bridging effect finer particles

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Filtration Behaviour

Retention of soil but not full clogging!• « Clogging »: the voids of a medium are progressively filled by solid matter to the point that the passage of water is restricted.

• Internal Clogging:- By mineral particles.- By precipitation and chemical deposition in the voids by water containing iron, de-icing salts.- By biological growth encrustation in aerobic conditions.

Both result in a decrease in the hydraulic conductivity.

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2929

Sample of non-wovenwith partial clogging

3030

Performance test : Long-Term Flow Test(to assess clogging/piping risk)

Outlet

OverFlow

Soil

Geotextile

Constant Head

• Simple

• 10 to 1,000 Hours

• Initial SoilCompaction

• RepresentativeGradient flow

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3131

Koerner, 1994; Bhatia et al 1990

Flow

Rat

e (V

ol/T

ime)

Log Time (Hrs)1 10 100 1000

A

B

C

B - Piping

A - Stable

C - Clogging

Results from Long-Term Flow Test

3232

Standard test:

Gradient Ratio Test

(ASTM D5101)

Outlet

Soil

Geotextile

Constant Head

• Corps of Engrs

• Benefit = 24 hrs test

• Measure Hydr Heads

• Determine Head Loss

• Calc Gradient Ratio

Manometers

2"

1"

A

B

C

Gradient Ratio =

HeadB - HeadC25 mm

HeadA - HeadB50 mm

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3333

GR Implications< 1 Piping= 1 Stable > 1 Clogging> 3 Severe Clogging

- Gradient Ratio, GR < 1

- Mass of Piped Particles, Mp < 2500 g/m2

Fannin, et al., (1994):

Gradient Ratio Acceptance Criteria:

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Tentative of modelizationof the retention of soil particles through the geosynthetic thickness

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3535

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ConstrictionsConstrictions

Diameter of incribed circlesbetween fibers

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3737

0

2

1

mm

Soil sideConstrictions dans

une couche unitaire

(3 ensembles de 8 trousde même taille)

Ouvertures de l’empilement de 3 couches unitaires :Tailles minimalesdes constrictions rencontrées le long d’un chemin d’écoulement

couche unitaire

couche unitaire

ModellingModelling ofof a a GeotextileGeotextile as a as a stackstack ofof unit unit layerslayers((FaureFaure--GourcGourc))

Modelization of the retention of soil particlesthrough the geosynthetic thickness

Particle likely to cross the geotextile thickness

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Opening Size « O »

Diameter of the biggest particlelikely to cross the geosynthetic

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3939

One of the standard testsOne of the standard testsfor “Opening Size” measurementfor “Opening Size” measurement

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0

10

20

30

40

50

60

70

80

90

100

0.0100.1001.000

Diameter of Opening (mm)

Perc

ent F

iner

Heavy Wt GT

Lite Wt GT

95

O95 O95

Of O95 = Size such as 95% soil mass passes

Opening SizeSoil passing through the geosynthetic

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Basic Basic RetentionRetention criterioncriterion

( ) ( )soil85 or 95filterf dO ≤

Of opening size of the filter

d85 or 95 representative of the biggest soil particles

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40

60

80

100

120

140

160

0 1 2 3 4 5 6

Epaisseur du géotextile (mm)

Ouv

ertu

re d

e fil

trat

ion

max

imum

(µm

) Geotextiles • same structure (n, df)• different thickness

(Faure-Gourc)

Geotextile thickness

Opening size

Variation of « opening size » with non-woven geotextile thickness

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0

200

400

600

800

0 1 2 3 4

Of/d85

toile de tamis

tissé de bandelettes

non-tissé

Masse de sol passé (g/m2)

σ = 100 kPai = 1

Performance test:Influence of the geosynthetic structure

on the loss of soil mass

Faure, 1988

Outlet

OverFlow

Soil

Geotextile

Constant Head •

•

Loss of soil mass

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Normal hydraulic conductivityNormal hydraulic conductivity

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PERMITTIVITY, Ψ (Cross-Plane Flow)

Darcy’s Law q = kiA

= kn∆h/t A

ψ = kn/t = q/∆h*A

ψ = Permittivity, s-1

ASTM D 4491 Water Permeability of Geotextiles by Permittivity.

qGeotextile

4646

ψallow =ψult

FSCB * FCR * FIN * FCC * FBC

FSCB = soil clogging and blinding (2 to 10)

FCR = creep (1 to 3)

FIN = intrusion (1.0 to 1.2)

FCC = chemical clogging (1.0 to 1.5)

FBC = biological clogging (1 to 10)(for geotextiles, Koerner 1998)

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Applications of geosynthetics

as FILTERS

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Bank protection

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4949

FilterFilter for for bankbank protectionprotection

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Silt fence

Sediments

Geotextile

Sediment-carrying

sheet runoff

Water surface

“Clear” water

Turbid water

Mai

n su

ppor

t pos

ts

Clo

gged

fabr

icFl

ow

H

X

h1

h2

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5151

Sand Containement for control erosion (Atlantic Ocean,France)

5252

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5353

Cross section of the Cross section of the ValcrosValcros damdam

8177,7

611:3

1:3

dowstream sampling zone

upstream sampling zone

draingeotextile

needlepunched non-woven (300 g/m²)

geotextile needlepunchednon-woven (400 g/m²)

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Valcros Dam (France) - 1970

1970 : First dam (20 m) with Geotextile filters

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Dam of Samira (Niger) H : 18 m - 2001

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--33--DrainageDrainage

-To transfer water,leachate, gazalong the geosynthetic ( in its thickness)

-Adequate flow capacity under design loads to convey maximum anticipated seepage during design life.-Long-term performance considerations.

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5757

GEONETS

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Geonets can convey liquid and gas within their channels.

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5959

The drain core of a geocomposite can also be:

GEOMAT CUSPATED SHEET

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Transmissivity, Ө or Flow Rate, q

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TransmissivityTransmissivity, , θθ

t

FlowRate

q

FlowRate

q

w

L

Dh

θult = (k x t)

Lhi ∆=

“In-Plane” Flow

Flow Rate, qult(Use for high flow volume materials)

or

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Normal compressive stress (kPa)

Variation of transmissivity with normal stress

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6363

GeonetsGeonets and geotextiles and geotextiles

can be installed separately or can be installed separately or can be combined can be combined

to form a drainage geocomposite.to form a drainage geocomposite.

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GEOCOMPOSITE

Geotextile filter

Geonetdrain

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Normal Stress and Intrusion Effects for a geocomposite

Polymeric Ribs

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Performance of a drainage geocomposite

Plastic core

Geotextile

Transports waterto the collectordrain

Protects waterproofing from damage when trench is backfilled

Retains its drainage capacity even under high earth pressure

Removes excess water from the soil

Prevents the collectordrain from silting upwith fine soil particles

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θallow =θult

FCR * FIN * FCC * FBC

FCR = creep (1.0 to 2.5)

FIN = intrusion (1.0 to 2.5)

FCC = chemical clogging (1.0 to 2.0)

FBC = biological clogging (1.0 to 10)(For Drainage Composites, Koerner 1998)

Transmissivity:

6868

Highway edge drain

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6969

Geocomposite Drain

Filter

Retaining structure

7070

Drainage behind a retaining structure

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7171

14lWeephole14lWeephole14lWeephole

Filter Application - Wall Drains

7272

FILL(Draining) SETTLEMENT

de

CO

MPR

ESSI

BLE

SOFT

CLA

Y

DRAINING LAYER

H

Vertical Consolidation Drains (wick drains)

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7373

Typical core structures

for wick drains

7474

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7575

mini-drain

filter

Non wovenlayer

Distance entre mini- drains

d= 0.25 , 0.50, 1 , 2 m

Specific drainage geocomposite

7676

Drainagebeneath an embankment

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7777

Fluid transferts in a landfillmany applications for geosynthetics

Gravity flow

Run-off

Waste

Collection of biogaz

Bottom & Slopesliners

RainfallTop cover

Leachate

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geopipe

geopipe

Confinement of waste , using mineral / geosynthetic barriers

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7979

Leachate drainage

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GEONET LEAKAGE DETECTION LAYER

GEONET

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Key Properties for Geosynthetics in Key Properties for Geosynthetics in Drainage and Filtration ApplicationsDrainage and Filtration Applications

TransmissivityTransmissivity, , θθ, in, in--plane permeability, kplane permeability, k

Permittivity, Permittivity, ψψ, cross, cross--plane permeability kplane permeability k⊥⊥

Opening Size Opening Size (AOS or EOS)(AOS or EOS)

Index Tests Index Tests vsvs Performance TestsPerformance Tests

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Thank you very much for yout attention.

Enjoy the Yokohama 8th ICG !

A special thank you to my colleaguesfor their documents used for this training course:

J.Bowders,Y.H.Faure,J.P.Giroud,B.Koerner,A.Rollin,…