1International Geosynthetics SocietyIGS Education Committee

Training Course on Geosynthetics Shanghai, 2008

Geosynthetics Types Functions/Applications

Prof A BouazzaProf. A. BouazzaMonash University, Melbourne

Australia

What are geosynthetics?

Synthetic polymer materials that are specifically manufactured to

What are geosynthetics?

GeosyntheticsPermeable Impermeable

Synthetic polymer materials that are specifically manufactured to be used in geotechnical and geo-environmental applications

Geotextiles Geomembranes

Geosynthetics Types

Geotextiles (woven nonwoven) Geotextiles (woven, nonwoven) Geogrids Geocells Geodrains Geofoam Geomats Geonets Geonets Fibres Geomembranes Geocomposites

Roles of Geosynthetics

Separator Reinforcement Drainage Filter Energy absorber Container Barrier

2Overview of Functions

Geosynthetics applications can be classified according to primary functions

However, it is important to note that geosynthetics may also perform one or more secondary functionsmay also perform one or more secondary functions

Function vs. Geosynthetic Type

Type of Geosynthetic

Separation Reinforcement Filtration Drainage ContainmentGeosynthetic

geotextile geogrid geonet geomembrane geosynthetic clay liner

geopipe geofoam geocomposite

Geosynthetics TypesGeotextiles

G t til ti h t f k itt d tit h b d dGeotextiles are continuous sheets of woven, nonwoven, knitted or stitch-bondedfibres or yarns. The sheets are flexible and permeable and generally have theappearance of a fabric. Geotextiles are used for separation, filtration, drainage,reinforcement and erosion control applications.

Nonwoven Woven

3Geosynthetics TypesGeogrids

Geogrids are geosynthetic materials that have an open grid-likeg g y p gappearance. The principal application for geogrids is the reinforcement ofsoil.

Geosynthetics TypesFibresDefinition: Pieces of fibres or continuous fibres or filaments mixedDefinition: Pieces of fibres or continuous fibres or filaments mixed to the soil for reinforcement

Geosynthetics TypesGeonets

Geonets are open grid-like materials formed by two sets of coarse,parallel, extruded polymeric strands intersecting at a constant acuteangle. The network forms a sheet with in-plane porosity that is used tocarry relatively large fluid or gas flows.

FOTO***

4Geosynthetics TypesGeocomposites

Geocomposites are geosynthetics made from a combination of two ormore geosynthetic types. Examples include: geotextile-geonet;geotextile-geogrid; geonet-geomembrane; or a geosynthetic clay liner(GCL). Prefabricated geocomposite drains or prefabricated vertical drains(PVDs) are formed by a plastic drainage core surrounded by a geotextilefilter.

geotextile geogrid

geomembrane geotextile

Geosynthetics TypesGeocomposites for Drainage

Geosynthetics TypesGeodrainsDefinition: Drainage materials consisting of a plastic core envelopedby a non woven (resin bonded) geotextile.

Geosynthetic TypesGeocells

Geocells are relatively thick three-dimensional networks constructed

soil confinement

Geocells are relatively thick, three dimensional networks constructedfrom strips of polymeric sheet. The strips are joined together to forminterconnected cells that are infilled with soil and sometimes concrete. Insome cases 0.5 m- to 1 m-wide strips of polyolefin geogrids have beenlinked together with vertical polymeric rods used to form deep geocelllayers called geomattresses.

5Geosynthetics TypesGeomats

Definition: Three dimensional, permeable, polymeric (synthetic or natural), p , p y ( y )structure, used for soil protection and to bind roots and small plants for

erosion control applications.

Geosynthetics TypesGeospacers

Definition: Three-dimensional polymeric structure with large voidspaces used in contacts with Soil/rock and/or any other geotechnicalmaterial in civil engineering applications.

geotextile

geospacer

Geosynthetics TypesGeofoam

Geofoam blocks or slabs are created by expansion of polystyrene foam

geofoam

soft soil

to form a low-density network of closed, gas-filled cells. Geofoam is usedfor thermal insulation, as a lightweight fill or as a compressible verticallayer to reduce earth pressures against rigid walls.

Typical Density:12 kg/m3 to 30 kg/m3

Geosynthetics TypesGeomembranes

Geomembranes are continuous flexible sheets manufactured fromone or more synthetic materials. They are relatively impermeable andare used as liners for fluid or gas containment and as vapour barriers.

6Geosynthetics TypesGeomembranes

rough surfacesmooth surface

Geosynthetics TypesGeosynthetic Clay Liners - GCL

Geosynthetic clay liners (GCLs) are geocomposites that areGeosynthetic clay liners (GCLs) are geocomposites that areprefabricated with a bentonite clay layer typically incorporated between atop and bottom geotextile layer or bonded to a geomembrane or singlelayer of geotextile. Geotextile-encased GCLs are often stitched or needle-punched through the bentonite core to increase internal shear resistance.When hydrated they are effective as a barrier for liquid or gas and arecommonly used in landfill liner applications often in conjunction with ageomembrane.

ypes of Geosynthetic Clay LinersGeosynthetics TypesGeosynthetic Clay Liners - GCL

Bentonite

(a) Stitch bonded bentonite between upper and lower GTX

Bentonite

(b) Needle punched bentonite through upper and lower GTX(b) Needle punched bentonite through upper and lower GTX

(c) Adhesive bound bentonite to a geomembrane

Bentonite + Adhesive

Geosynthetics TypesGeosynthetic Clay Liners - GCLBentonite: Hydraulic conductivity 10-11 m/sGCL combination of geosynthetics and bentonite

Bentonite expansion after hydration

7Geosynthetics Applications

Barrier Drainage Filtration Protection Reinforcement Separationp Surficial erosion control Multiple functions

Fluid/Gas (barrier) containment: The geosynthetic acts as a relatively

Geosynthetics ApplicationsBarriers for Fluids and Gases

Fluid/Gas (barrier) containment: The geosynthetic acts as a relativelyimpermeable barrier to fluids or gases. For example, geomembranes,thin film geotextile composites, geosynthetic clay liners (GCLs) and field-coated geotextiles are used as fluid barriers to impede flow of liquid orgas. This function is also used in asphalt pavement overlays,encapsulation of swelling soils and waste containment.

geosyntheticbarrier

The use of a geosynthetic material to prevent the migration of liquids orgases.

Geosynthetics ApplicationsBarriers for Fluids and Gases

waste

geomembrane + drainage layer

geomembrane and/or GCL

Geosynthetics ApplicationsBarriers for Fluids and Gases

8Geosynthetics ApplicationsDrainage and Filtration

Drainage: The geosynthetic acts as a drain to carry fluid flows throughDrainage: The geosynthetic acts as a drain to carry fluid flows throughless permeable soils. For example, geotextiles are used to dissipate porewater pressures at the base of roadway embankments. For higher flows,geocomposite drains have been developed. These materials have beenused as pavement edge drains, slope interceptor drains, and abutmentand retaining wall drains. Prefabricated vertical drains (PVDs) have beenused to accelerate consolidation of soft cohesive foundation soils belowembankments and preload fills.

Filtration: The geosynthetic acts similar to a sand filter by allowing waterto move through the soil while retaining all upstream soil particles. Forexample, geotextiles are used to prevent soils from migrating into drainageaggregate or pipes while maintaining flow through the system. Geotextilesare also used below rip rap and other armour materials in coastal and riverbank protection systems to prevent soil erosion.

Geosynthetics ApplicationsDrainage and FiltrationSubstituting or in combination with natural draining materials

capilarity barrierdrain

geotextile filtergeocomposite drainage layer

geosynthetic

Q

PVD

Geosynthetics ApplicationsDrainage and Filtration

Geocomposite behind a retaining wall (Photo: Courtesy J.P. Gourc)

Geosynthetics ApplicationsDrainage and Filtration

9Geosynthetics ApplicationsProtection

Protection: The geosynthetic material is used as a localised stressg yreduction layer to prevent or reduce damage to a given surface orlayer.

geomembrane

geomembrane

geomembrane

protective geotextilelayer

nonwoven geotextile

Geosynthetics ApplicationsReinforcement

Reinforcement: The geosynthetic acts as a reinforcement element withina soil mass or in combination with the soil to produce a composite thathas improved strength and deformation properties over the unreinforcedsoil. For example, geotextiles and geogrids are used to add tensilestrength to a soil mass in order to create vertical or near-vertical changesin grade (reinforced soil walls).

Reinforcement enables embankments to be constructed over very softyfoundations and to build embankment side slopes at steeper angles thanwould be possible with unreinforced soil. Geosynthetics (usuallygeogrids) have also been used to bridge over voids that may developbelow load bearing granular layers (roads and railways) or below coversystems in landfill applications.

Geosynthetics FunctionsReinforcementReinforced mass: stronger and stiffer

geosynthetic

Reinforced mass: stronger and stiffer

geosynthetic

Geosynthetics ApplicationsReinforcementReinforced Walls and Steep Slopes

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Geosynthetics ApplicationsReinforcementFibre Reinforced Soil

continuous filaments

discrete fibres

fibre reinforced backfill

Geosynthetics ApplicationsReinforcementEmbankments on Soft Soils

reinforcementFactor of safety increases

Better distribution of stressesto the soft foundation

fillfill

soft soil

Geosynthetics FunctionsReinforcement

Geosynthetics ApplicationsEmbankment Stabilisation

pilecap

softil

geosynthetic layer

soil

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Geosynthetics ApplicationsReinforcementReinforced pavements/caps

geosynthetic reinforcement

geosyntheticcap

Geosynthetics ApplicationsMultiple FunctionsPavements: Reflective cracking prevention

P ti f i f fiPrevention of pumping of fines

new capnew capgeosynthetic

old cap

geosynthetic sealcracks

Pumping of fines

Geosynthetics ApplicationsMultiple Functions

Geogrid application in overlaysg pp y Geotextile application in overlays

Geosynthetics ApplicationsMultiple Functions

pp y

Rezende (2002)

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Geosynthetics ApplicationsMultiple Functions

Without geotextile With geotextile (some cracksbut no pumping of fines

Geosynthetics ApplicationsSeparation

Separation: The geosynthetic acts to separate two layers of soil that havep g y p ydifferent particle size distributions. For example, geotextiles are used toprevent road base materials from penetrating into soft underlying softsubgrade soils, thus maintaining design thickness and roadway integrity.Separators also help to prevent fine-grained subgrade soils from beingpumped into permeable granular road bases.

separator(geotextile)

fill

soft soil

(geotextile)

Without geotextile With geotextile

Geosynthetics ApplicationsErosion Control

Erosion control: Geosynthetics can minimise soil erosion caused byrainfall impact and surface water runoff. For example, temporarygeosynthetic blankets and permanent lightweight geosynthetic mats canbe placed over exposed slope surfaces. Geotextile silt fences can beused to remove suspended particles from sediment-laden runoff water.Some erosion control mats are manufactured using biodegradable woodfibres.

geocellgeotextilegeomat

Geosynthetics ApplicationsErosion Control

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Geosynthetics Other Applications

Geotextile Tubes: used for containment, erosion control, water and

geotextile

sand

flood control, etc.

Narrowneck Reef - Australia

Surfers Paradise 1999-2001

370 100-300t mega containers

Needle-punched nonwovens

Courtesy of Soil Filters Pty. Ltd. & Naue Gmbh

Geosynthetics Other Applications

Protection Against Falling Stones and Avalanches

geosynthetic reinforced fill

Protection Against Falling Stones and Avalanches

Geosynthetics Other ApplicationsNoise Reduction Barrier

geosynthetic reinforced fill

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Geosynthetics Emerging ApplicationsElectrokinetics GeosyntheticsDefinition: Drainage materials associating an electrically conductivegeosynthetic which allows soil consolidation by electro-osmosis.

Jones et al. (2005)

Enhanced Soil Vapor Extraction Using PV Drains

VentVent

Extraction

Abuel-Naga, Bouazza, Bowders, Collazos (2008)

Flow VaporLines

Surface Seal

Extraction PVD

Vent PVD

Lines

Ri

Geosynthetics Emerging Applications

geotextile

Alexiew et al

geosynthetic encasedcolumns

sand or gravel

Alexiew et al. (2004)

Trunk et al. (2004) Eurogeo04

geogrid

Gniel & Bouazza (2008)Eurogeo08

Conclusions

No standard solutions. Each application asks for individual design.

There is no one size to fit them all

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Sources for geosynthetics information

Technical papers published in Geosynthetic International, Geotextiles & Geomembranes, Geosynthetics (ex GFR), etc.

www.geosyntheticssociety.org