GEOTEXTILES

• A geotextile is a synthetic permeable textile material used with soil, rock, or any other geotechnical engineering related material.

• Geo textiles also called geosynthetics, are generally associated with high-standard all-season roads, but can be used in low-standard logging roads.

• A geotextile is designed to be permeable to allow the flow of fluids through it or in it, and a geomembrane is designed to restrict the fluid flow.

TYPES OF GEOTEXTILE

• In general, the vast majority of geotextiles are made from polypropylene or polyester formed into fabrics as follows:

1) Woven monofilament 2) Woven multifilament 3) Woven slit-film monofilament 4) Woven slit-film multifilament 5) Nonwoven continuous filament heat bonded6) Nonwoven continuous filament needle-punched7) Nonwoven staple needle-punched 8) Nonwoven resin bonded 9) Knitted

Applications:

• Modern geotextiles are usually made from synthetic polymers- polypropylenes, polyesters, polyethylene's, and polyamides - which do not decay under biological and chemical processes.

• This makes them useful in road construction and maintenance.

Polyester Polyamide Polypropylene Polyethylene

Strength H M L L

Elastic modulus H M L L

Strain at failure M M H H

Creep L M H H

Unit weight H M L L

Cost H M L L

Resistance to:

U.V. light stabilized H M H H

unstabilized H M M L

Alkalis L H H H

Fungus, vermin M M M H

Fuel M M L L

Detergents H H H H

Non-Woven• The nonwoven fabric, which looks like a felt fabric, is an

arrangement of fibres either oriented or randomly patterned in a sheet.

• Materials commonly made out of non-woven fabric include upholstered furniture coverings and cloth interiors of automobiles.

• These fabrics can be manufactured in a variety of ways, bonding fibres together using chemical, thermal or mechanical processes.

• Non-woven geotextile fabric is more likely to stretch than woven geotextile.

• It has the ability to let water flow along the plane of the geotextile.

Woven geo textile

• The woven geotextile, which looks like burlap, is a sheet made of two sets of parallel strands systematically interlaced to form a thin, flat fabric.

Geo Textiles in Road Industry

• In the road industry there are four primary uses for geotextiles: 1) Separation2) Drainage 3) Filtration 4) Reinforcement

• In separation, inserting a properly designed geotextile will keep layers of different sized particles separated from one another.

• In drainage, water is allowed to pass either downward through the geotextile into the subsoil, or laterally within the geotextile which functions as a drain.

• In filtration, the fabric allows water to move through the soil while restricting the movement of soil particles.

• In reinforcement, the geotextile can actually strengthen the earth or it can increase apparent soil support. For example, when placed on sand it distributes the load evenly to reduce rutting.

• Geotextiles now are most widely used for stabilizing roads through separation and drainage.

• When the native soil beneath a road is very silty, or constantly wet and mucky then its natural strength may be too low to support common traffic loads, and it has a tendency to shift under those loads.

• Geotextiles keep the layers of sub grade and base materials separate and manage water movement through or off the roadbed.

Geotextiles in separation

• Two important criteria for selecting a geotextile for separation are permeability and strength.

• The geotextile used for separation must allow water to move through it while retaining the soil fines or sand particles.

• It should let water pass through it at the same rate or slightly faster than the adjacent soil.

• It must also retain the smallest soil particle size without clogging or plugging.

• In selecting a specific geotextile for separation we must consider its basic strength properties, grain size distribution of the sub grade and the sub base and the permeability of the geotextile.

Required properties for separationMechanical Hydraulic Long-term

Performance

During installation

Impact resistance

Elongation at break

Apparent opening

size ( A.O.S.)Thickness

UV resistance

During construction

Puncture resistance

Elongation at break

Apparent opening

size ( A.O.S.)Thickness

Chemical stability

UV resistance

After completion of construction

Puncture resistance

Tear propagation resistance

Elongation at break

Apparent opening

size ( A.O.S.)Thickness

Chemical stability

Resistance to decay

Stabilization

• Higher strength woven and nonwoven geotextiles provide stabilization in addition to the primary function of separation.

• Through stabilization, a geotextile can increase the effective bearing capacity of low strength subgrade soils.

• A stabilization geotextile reduces subgrade pumping, over-excavating and required aggregate thickness.

• Stabilization geotextiles substantially reduce construction costs for paved and unpaved roads.

• For example, unpaved road aggregate thickness can be reduced by as much as 30% to 50% when a stabilization geotextile is used.

Geo textiles in pavement Repair:

• A major contributor to roadway deterioration is water beneath a pavement which softens subgrade soil which destroys pavement structural capacity.

• A pavement with a base which becomes saturated as little as 10% of the time will only have 50% of the life of a pavement where water is kept out of the base.

• Most of this water enters through cracks and pores in the pavement surface.

• Paving fabrics and repair membranes are engineered to reduce water infiltration and reflective cracking, thereby saving on costly repaving cycles.

• They have been proven to extend the life of highways, city streets, parking lots, and airport runways and taxiways.

• These kind of geotextiles are used in new asphalt pavements, beneath overlays of rigid and flexible pavements, and beneath chip-seal pavements.

• A needle punched, nonwoven polypropylene paving fabric which provides a moisture barrier over the full width of the paving surface when combined with an asphalt cement tack coats sub grade.

• It helps in extending pavement life while reducing maintenance costs.

Geo textiles in retaining Walls

• Retaining walls help to maximize their land use.• However, building a concrete gravity or crib wall is

often impractical because of their high construction cost.

• Geotextiles are used for a wide assortment of reinforcement applications, including embankments over soft soils, levees and retaining walls.

• Geotextiles are well-suited to construction of walls with timber, precast panel and segmental block facing.

• In fact a geotextile retaining wall can be built for less than half the cost of a conventional wall.

• Woven geotextiles offer other significant advantages over conventional methods, such as simplified installation and construction, and the ability to use on-site backfill material.Polypropylene geotextiles cost approximately half the amount of polyester and polyethylene geogrids, and they require considerably less labor to install.

Geo textiles subsurface Drainage

• Geotextiles have replaced graded soil filters for drainage of virtually all structures, including groundwater intercept systems, pavements, building foundations, dams and walls.

• Compared to conventional soil filters, geotextiles offer advantages by providing a consistent and continuous filter, reduced excavation, reduced environmental impact, simplified, higher quality construction and a substantial reduction in material costs.

Mechanical Hydraulic Long-term Performance

Permanent drainage function

Influence of normal overburden pressure

PermeabilityThickness

Apparent opening size (A.O.S.)

Chemical properties of water and soilChemical stabilityDecay resistance

Temporary drainage function

Influence of normal overburden pressure

Permeability Thickness

Apparent opening size (A.O.S.)

• Both woven and nonwoven geotextiles perform well when draining stable, coarse-grained soils.

• Nonwovens are generally used when the retention of fine soil particles is critical to the performance of the drainage system.

• Geotextile strength properties are selected to ensure that the geotextile survives construction and remains intact to perform as a filter.

Geo textiles erosion Control

• Geotextiles have replaced graded granular filters used beneath riprap or other armor materials in revetments.

• Applications include drainage channels, shorelines, and bridge and pier scour protection systems.

• Without a geotextile filter, wave action and water movement erode subgrade soils from beneath the riprap or armor.

• Degradation of the subgrade negates the benefit of the riprap or armor, resulting in extensive repair and replacement.

• The selection of geotextiles for permanent erosion control is similar to subsurface drainage.

• However, permanent erosion control applications usually require higher geotextile strength properties.

• The geotextile must survive placement of possibly very large, angular riprap, plus be able to endure severe wave action.

Geo textiles waste Containment

• Waste containment and environmental cleanup projects demand geotextiles with uncompromising physical properties and consistent product quality.

• In environmental applications, geotextiles must retain these critical properties while exposed to harsh chemical environments.

• Waste containment fabrics serves in a variety of environmental applications, including filtration of fluid and gas collection systems, protection of geomembrane liners, waste daily covers and reinforcement.

• Geotextiles are specified for municipal waste and hazardous waste landfills, heap leach pads, sewage treatment lagoons, as well as waste containment ponds and other surface impoundments.

Geo textiles railroad Stabilization

• Maintaining track bed geometry is critical for efficient railroad operation.

• Subgrade pumping into the overlying ballast can create an uneven track bed, resulting in delayed arrivals and even derailments.

• Geotextiles perform multiple functions in railroad applications.

• Nonwoven fabrics are used to stabilize both new and rehabilitated tracks.

• They prevent contamination of new ballast with underlying fine-grained soils and provide a mechanism for lateral water drainage.

• Using nonwoven geotextiles beneath track beds ensures that the ballast can sustain the loads for which it was designed.

• These geotextiles are used in all track applications, including switches, turnouts and grade crossings.

• High-strength woven geotextiles can also be used to reinforce weak subgrade soils and reduce required embankment fill materials.