geosynthetics types and functions

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  • 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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