Geotextiles in Civil Engineering: Classification, Functions and Application

#Geotextiles are made from polypropylene, polyester, polyethylene, polyamide (nylon), polyvinylidene chloride, and fiberglass. Polypropylene and polyester are the most used. Sewing thread for geotextiles is made from KevlarL or any of the above polymers.Based on their structure and the manufacturing technique, geotextiles may be broadly classified into woven and nonwoven. Woven geotextiles are manufactured by the interlacement of warp and weft yarns, which may be of spun, multifilament, fibrillated or of slit film. Nonwoven geotextiles are manufactured through a process of mechanical interlocking or thermal bonding of fibers/filaments.

An important contribution of the textile industry to the civil engineer­ing sector is what is, according to their use, referred to as construction textiles or geotextiles. Geotextiles help in reducing energy consumption and improv­ing performances in the construction sector. Textile structures are also used in architectural sector to improve the aesthetics of buildings.

• Physical properties
• Mechanical properties
• Hydraulic properties
• Endurance, Degradation, and Survivability properties

Physical properties: 
The physical properties of geotextiles which are of primary concern are fiber composition, areal density, thickness, stiffness, and specific gravity. In geogrids and geonet, the properties such as structure type, junction type, aperture size, and shape are of prime importance. The structure of the geo­textile often dictates the application area for which the material is appro­priate. The physical properties of the geotextile are more temperature and humidity dependent.

Mechanical properties: 
Mechanical properties are important for the applications where a geotex­tile is required to perform as a load-bearing member under applied loads and where it is required to survive on-field installation related stresses. Mechanical properties of geotextile are often categorized as in-isolation properties and performance properties. In-isolation properties are deter­mined on the geotextiles itself with the absence of surrounding soil. Performance properties are determined on geotextiles in the presence of site-specific soil.

Hydraulic properties: 
The hydraulic properties of geotextiles are those that relate directly to filtration and drainage functions of geotextiles. The filtration function of a geotextile requires the pore size sufficiently small to retain the erodible soil particles and permeability adequate to allow the free passage of seepage from the protected soil. Filtration properties are controlled by pore sizes, pore size distribution, and porosity of the fabric. The permeability of the geotextile is determined by measuring the rate of flow of water through the fabric in the direction nor­mal to the plane of the fabric. Porosity, permittivity, and transmissivity are the most important hydraulic properties of geotextiles, geonets, and geocompos­ites, which are commonly used in filtration and drainage applications.

Endurance, Degradation, and Survivability properties:
The endurance, degradation, and survivability properties (e.g., creep behav­ior, abrasion resistance, long-term flow capability, durability—construction survivability, and longevity) of geotextiles are related to their behavior during service conditions, including time.

Types or Classification of Geotextile: 
Geotextile is divided by two ways. They are-

• According to Manufacture
• According to Time of Use

Classification of geotextiles based on manufacture: 
Geotextiles can be manufactured by weaving or knitting or nonwoven technologies. Geotextiles are classified as follows:

1. #Woven geotextiles: Woven geotextiles are produced with the interlacement of two sets of yarns at right angles in the weaving process. Woven geotextiles have high strengths and modulus in the warp and weft directions and low elongations at rupture.

2. #Knitted geotextiles: Knitted geotextiles are produced with the interlooping of one or more yarns in the knitting process. These geotextiles are highly extensible and have relatively low strength compared to woven geotextiles, which limits its usage.

3. #Nonwoven geotextiles: Nonwoven geotextiles are thicker than woven and are made either from continuous filaments or from staple fibers. They are produced in the following bonding techniques:

• Needle punching
• Thermal bonding
• Chemical bonding

4. #Stitch-bonded geotextiles: Stitch-bonded geotextiles are produced by interlocking fibers or yarns or both, bonded by stitching or sewing. Even strong, heavyweight geotextiles can be produced rapidly. Tubular geotextiles are manufac­tured in a tubular or cylindrical fashion without longitudinal seam.

5. #Geogrids: Geogrids are materials that have an open grid-like appearance. The principal application for geogrids is the reinforcement of soil.

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

7. #Geomembranes: Geomembranes are continuous flexible sheets manufactured from one or more synthetic materials. They are relatively impermeable and are used as liners for fluid or gas containment and as vapor barriers

8. #Geocomposites: Geocomposites are made from a combination of two or more geosyn­thetic types. Examples include geotextile-geonet; geotextile-geogrid; geonet-geomembrane; or a geosynthetic clay liner (GCL).

9. GCLs: GCLs are geocomposites that are prefabricated with a bentonite clay layer typically incorporated between a top and bottom geo­textile layer or geotextile bentonite bonded to a geomembrane or single layer of geotextile.

10. Geopipes: Geopipes are perforated or solid-wall polymeric pipes used for drain­age of liquids or gas.

11. #Geocells: Geocells are relatively thick 3-D networks constructed from strips of polymeric sheet. The strips are joined together to form intercon­nected cells that are filled with soil and sometimes concrete.

12. Geofoam: Geofoam blocks or slabs are created by expansion of polystyrene foam to form a low-density network of closed, gas-filled cells.

According to time of use: 

1st Generation: Geotextile that were being manufactured for another purpose, such carpet or industrial sacking, but later used for geo technical purpose are known as 1st generation geotextile.

2nd Generation: Geotextile that were manufactured for certain geo-technical purpose, but without adopting modern technology.

3rd Generation: Geotextile that was manufactured, designed, and produced to meet certain end use. It is actual geo-textile.

Functions of Geotextiles: 
#Geotextiles have numerous application areas in civil engineering including pavements, filtration and drainage, reinforced embankments, railroads, ero­sion and sediment control, moisture barrier, silt fencing, and earth-retaining walls. They always perform one or more of the earlier functions when used in contact with soil, rock, and/or any other civil structures. The basic func­tions of geotextiles are as given in the following sections.

Separation: 
Separation is the process of preventing undesirable mix-up of two dis­similar materials. The geotextile acts as a separating layer between fine aggregates and coarse aggregates or soils that have different particle size distributions to avoid undesirable mix-up. Separators also help to prevent fine-grained subgrade soils from being pumped into permeable granular road bases thereby keeping the structural integrity and functioning of both materials intact.

Fig: Geotextile in civil engineering

Filtration: 
#Geotextile is placed in contact with and down gradient of soil to be drained. The plane of the geotextile is positioned normal to the expected direction of water flow. To perform this function the geotextile needs to satisfy two conflicting requirements: the filter’s pore size must be small enough to retain fine soil particles while the geotextile should permit relatively unimpeded flow of water into the drainage media.

Drainage:
The geotextile acts as a drain to carry fluid flows through less permeable soils. The application of geotextiles in drainage applications has improved the economical usage of blanket and trench drains under and adjacent to the pavement structure, respectively.

Reinforcement: 
The geotextiles act as a reinforcement element within a soil mass or in combination with the soil to produce a composite that has improved strength and deformation properties over the unrein­forced soil. The geotextile interacts with soil through frictional or adhesion forces to resist tensile or shear forces.

Moisture and liquid barrier: 
The protection of civil structures from the effects of seeping water is a common need. The geotextiles acts as a relatively impermeable barrier to prevent the penetration of liquids or moisture over a projected service period.

Erosion control:
Erosion is the process by which soil and rock are removed from the earth’s surface by exogenetic processes such as wind or water flow, and then transported and deposited in other locations. The geotextile anchored in steep slope protects soil surfaces from the trac­tive forces of moving water or wind and rainfall erosion.

Applications of Geotextiles: 
The applications of geotextiles are numerous and continuously growing steadily. The various detrimental factors deteriorating the service life of roads and pavements including environmental factors, subgrade conditions, traffic loading, utility cuts, road widening, and aging. In an asphalt con­crete pavement system, the geotextile provides a stress-relieving interlayer between the existing pavement and the overlay that reduces and retards reflective cracks under certain conditions and acts as a moisture barrier to prevent surface water from entering the pavement structure that increases the life of the pavement. The presence of the geotextile restricts lateral move­ment of both the aggregate and the subgrade, improving the strength and the stiffness of the road structure.

Geotextile-reinforced retaining walls consist of geotextile layers as rein­forcing elements in the backfill to help resist lateral earth pressures. The con­struction of embankments over soft soils is a challenge for civil engineers. The placement of geotextile layer over the soft soil and construction of the embankment directly over it will consolidate the soft soil. Nonwoven paving fabrics have high elongation and low tensile strength and are used for stress relief. When saturated with asphalt, the flexible interlayer allows considerable movement around a crack but nullifies or at least lessens the effect the move­ments have on the overlay. The geotextile-reinforced foundation soils are being used to support footings of many structures including warehouses, oil drilling platforms, platforms of heavy industrial equipments, parking areas, and bridge abutments.

The control of water is critical to the performance of buildings, pavements, embankments, retaining walls, and other structures. Drains are used to relieve hydrostatic pressure against underground and retaining walls, slabs, and underground tanks and to prevent loss of soil strength and stability in slopes, embankments, and beneath pavements. Geotextiles retain the surrounding soil while readily accepting water from the soil and removing it from the area. Railway tracks serve as a stable guideway to trains with appropriate vertical and horizontal alignment. Geotextiles are used to stabilize the track.

Geotextiles are widely used in the construction of sports turf. Playing fields are synthetic grass surfaces constructed of light-resistant PP mate­rial with porous or nonporous carboxylated latex backing pile as high as 2.0–2.5 cm. Another synthetic turf sport surface made of nylon 6,6 pile fiber knitted into a backing of polyester yarn provides high strength and dimen­sional stability. Geotextiles are used for the improvement of muddy paths and trails those used by cattle or light traffic; nonwoven fabrics are used and are folded by overlapping to include the pipe or a mass of grit.