The concept of geotextiles

The concept of geotextiles

Meaning of geotextile
A geotextile is a synthetic permeable textile material applied with soil, rock, or any other geotechnical engineering related material. It is produced by synthetic fibers made in a woven or loose nonwoven form. Geotextiles, also named as geosynthetics, are normally applicable to high-standard all-season roads, can also be used to low-standard logging roads.

American Society for Testing and Materials (ASTM), describes geotextile as any permeable textile material applied with foundation, soil rock, earth or any other geotechnical engineering related material as an integral part of a: man-made project, structure or system.

Application

Geotextiles are mostly used for: Reinforcement of Unpaved Roadways, Paved Roadways, Separation applications in Unpaved Roadways, Paved Roadways, Sediment Control etc, as part of geo-composites.

Historical background of geotextile

Geotextiles are existed with more than fifty year. Though, the development of market and research work put in to practice in early 1960's. The first international conference on the application of fabrics in geotechnics was held at Paris in 1977.The Industrial Fabrics association International (IFAl) started geotechnical division in 1980.

The second international conference of geotextile was held at Las Vegas, sponsored by IFAI in 1982, where decision was taken to build an International Society of Geotextile (ISG) and later on ISG was created in 1983. ISG created a sub-committee SC-21 on geotextile (related to existing technical committee TC-38 on textiles); International Society for Soil Mechanics and Foundation Engineering (ISSMFE) agreed to formulate a technical committee on geotextile in 1983.

In 1992, The Indian Chapter of the International Geosynthetics Society (IGS) and the Committee for International Geosynthetics Society (India) - CIGSI were established and in 1998 the first Indian geotextile conference was held at Mumbai.

The basic functions of geotextiles
Geotextiles normally give the following functions:
.Separation/filtration
.Reinforcement
.Drainage
.Hydraulic or moisture barrier.
It is noted that due to wide changes in their characteristics of the materials for geotextile together with range of feasible fabric/grid structures, geosynthetics perform the above functions and provide considerable advantages over the conventional methods and materials.

Application-wise progression of geotextiles

Progression of the geotextiles can be generally classified into its various generations.

. The first generation geotextiles: The first generation of geotextiles used for such applications like carpet or industrial sackings.
. The second generation geotextiles: The second generation of geotextiles was made by the producers by selecting specific textiles with consideration of their appropriate geotechnical intention, but by means of conventional manufacturing techniques.
. The third generation textiles: The third generation textiles were then really intended and built up particularly for the purpose of geotechnical uses - specifically Directionally Structured Fibers (DSF), Directionally Oriented Structures (DOS) and composite products.

Geotextiles are performing progressively in civil engineering construction and are still growing as an alternative, economically viable material. In recent years, the utilization of geotextiles in the world markets has grown at extraordinary rate. In India, geotextiles have been specially used in road and airport flexible pavements and in overlays.

The growth of geotextiles in between 2000 and 2005 was grown at the rate of 4.6% annually, and during the next five years (i.e. up to 2010) it is predicted to 5.3 percent. The geotextile market is increasing in its growth rate, though these are now lower than previously forecasted and in compared to other applicators it has relatively little growth for end-user of textiles. In the quantity, geotextiles reported a little growth, more than 250,000 tons in 2000, merely 1.5 percent of the overall technical textile market. Furthermore, this sector with low unit values in small numbers gives a large margin.

Description of basic functions of geotextiles

The important functions of geotextiles as mentioned above are briefly described below:

Separation

The separation task means, the separation of two different soils, by avoiding intermixing of the two soils during the life of the structure. Geotextiles, when placed between fine soil and a coarse material (gravel, stone, etc), it averts the soil from blending and entering into the coarse material under the proceedings of repeated applied loads, hence it confirms mechanical nature of the coarse-grained soil is retained. Geotextiles are generally applied for separation when applied in roadway pavement sections. For separation, a proper geotextile must therefore be settled yet deformable; have a mass per unit area and strength that can resist mechanical stresses while installation without any damages and at the same time acts as a filter.

Filtration: As a filter, geo-textile permits liquid to pass to its own plane while avoiding the largest part of the soil particles. For this two cases may be applicable:

.a geotextile put across the flow of liquid in the associated region between two types of soils having diverse grain sizes,
.a geotextile positioned in contact with soil permits water leaking from the soil to pass through, while averting any transfer of soil particles, such as in drainage pipes.

The volume of water transferring through the fabric is a vital mechanism in the filtration process. Therefore, over a long period of time geotextile must have high access for water permeability. It must have a capable space width, which restrain any eroding granules. The mass per unit area and strength should oppose mechanical loading from the soil without being spoiled during laying.

Impermeabilisation: A geotextile with tetra-hydro-furan adhesive for seaming or a bentonite impervious mat and geocomposite like PVC plastic membrane controls any leakage of fluid across and it gives impermeabilisation to the structure.

Moisture barrier: A few of the olefin fibers of hydrophobic type can be exploited to avert the moisture in seeping and distressing fine soil structure.

Geotextile materials

Geotextiles are mainly made from polyolefin, are light in weight and strong but cheap. These permeable woven geotextiles are generally used for filtration and impermeable membranes to hold out mud pumping. Certain fabrics provide high puncture resistance and offer a significant recognition in road and rail construction projects, or where the reliability of the sheet is required, as in landfill sites.

It is noted that geotextiles have to be made in large quantities and that too cost-effectively, fibers for geotextiles are normally produced by melt-spinning. High Density Polyethylene (HDPE) is applied to receive reinforcement needs. Even staple fibers, monofilaments, multifilament yarns and slit films are also applied.

The polymers as they are actually made and applied for geotextile production are not available in their chemically pure form. For example, raw polyethylene in its colorless translucent form is rather subjected to light degradation; therefore, it is not applied as geotextiles applicants, but normally includes carbon black as ultraviolet (UV) light stabilizer. It is possibly the most light-resistant polymer in black form.

Based on manufacturing process, geotextiles can be categorized as woven, nonwoven, or knitted. Woven fabrics are made by the traditional weaving method, giving a screen-like or mesh material with a variety of sizes of mesh openings and according to the tightness of weave. A woven fabric gives high tensile strength, high modulus, and low strains, but gives poor abrasion resistance and dimensional stability.

While nonwoven fabrics have high permeability and high strain characteristics. They are produced in a number of geometric and polymeric compositions to satisfy a various applications. Many geotextiles are prepared by polypropylene. Fabric produced concrete revetment mats; silt filter fences, erosion control blankets, and fabric envelopes for pipe or mat under drains are the illustrations of common geotextile applications. A geotextile's long-term representation is due to the durability and creep characteristics of the polymer structure. The effect of ground, weather, sunlight, and aging conditions must be measured when applying a geotextile for a permanent base. Non-woven Geotextiles are available in the form of polypropylene fibers and are needle punched. Nonwoven fabrics possess distinctive ability to lengthen locally to resist damage, superior permeability and frictional resistance, though their tensile strength is lower than that of woven fabrics.

Knitted textiles exposed its fewer applications as geotextiles. Though, warp knitted fabrics are important for developed into reinforced soil applied for granular soil and are named as Directionally Structured Fibers (DSF). DSF directed to considerable economies in the application of polymer within the construction, in the form of its evidence for the absorption of tensile stresses. While examine, significantly less stress is to be found on weft element, then there is little grounds. Similarly Directionally Oriented Structures (DOS) are warp knitted fabrics with comparable sets of yarns put into the structure included by loop structures so that load is exactly put on the yarns to use their full potential.

Geomembranes stand for another form of geosynthetics and are applied mainly for linings and covers of liquid or solid-storage facilities. These are basically a resistant material, in the shape of manufactured sheet, which may be synthetic, bituminous or bentonitic. Therefore, the main task is as a liquid or vapor barrier and is also applicable for various applications.

Applied for decorative water feature application and land design and recognized as flexible geomembranes as liners. This is because of the reality that the flexible geomembrane is cheap and flexible for many design ideas, besides having water containment capabilities.

Geogrids

Geogrids are polymeric structures rather than being a woven, nonwoven or knit textile fabric, in their unidirectional or bidirectional format. They are made in the form of manufactured sheet, including a regular network of integrally associated parts, which may be linked by extrusion, bonding or interlacing, whose openings are larger than the constituents, made into a extremely exposed, network like arrangement, i.e. they have large apertures. They work as reinforcement materials. Coated polyester geogrids have been broadly applied in soil stabilization and geotechnical reinforcement uses. Their physical structure can be categorized in to the following:

.Unidirectional geogrid: Having a great deal of tensile strength in one direction (longitudinal or transversal) than in the other direction.
.Bidirectional geogrid; Having identical strength in both longitudinal and transversal direction.
.Extruded geogrid: Created through stretching uniaxial or biaxial, an extruded integral structure.
.Bonded geogrid: Created through bonding, at right angles, two or more sets of strands.
.Woven geogrid: Created through interlacing, usually at right angles, two or more yarns, filaments or other elements.

Geonets

Geonets or geospacers are normally made by uninterrupted extrusion of corresponding sets of polymeric ribs at acute angles to one another. When the ribs are opened, relatively large apertures are shaped into a netlike pattern. Their pattern work is mostly applicable in the drainage area.

Geocomposites

A geocomposite comprises with a mixture of geotextile and geogrid; geogrid and geomembrane; geotextile; or any of these three materials with [another material (e.g. deformed plastic sheets, steel cables, or steel anchors). Geocomposites are accumulated materials, in the appearance of manufactured sheet or strip, compromising of at least one geosynthetic among the components.

Geomat

Geomat is available in the polymeric form, in the shape of a manufactured sheet, compromising of an irregular network of fibers, yarns, filaments, tapes or other elements (thermally or mechanically connected), whose openings are normally greater than the application of the constituents.

Geocell

Geocell is available in a polymeric cellular form including a regular open network of connected strips, linked by extrusion, adhesion or by other methods.

Biomat and Bionet

They are permeable, natural, and accepted as biodegradable polymeric materials, in the shape of a manufactured sheet. Normally biomat comprises with fibers (jute, coir, sisal, straw, or others) set aside collectively by one or two layers of synthetic or natural meshes and bionet comprises with a regular network of knotted or interlaced yarns, whose openings are normally greater than the constituents.

Geotextiles available in the natural form

Jute
Jute is natural multi filament fiber, durable and simple to both produce and dispose. Biodegradable woven jute is accessible in a number of weave densities, initially anticipated as a geotextile to avoid land sliding and consequent to deforestation. Jute is available in India in large quantities at a cheaper rate. Jute geotextiles can perform a vital function in the control of soil erosion by revegetation and it has many uses, which are cheaper well as easy to accomplish. It has many benefits as geotextiles, because of its high water absorption capability, flexibility and drapability. It also mixed with other materials, such as in the construction of 'jute-sand-mat' structures.

The growth of jute based geotextiles is huge due to its various applications in infrastructure development. There were eight Indian jute mills which started production of jute on the base of 50 tons a day of geotextiles with open mesh structures in June 1998, and in the recent time production and uses of these types of jute geotextiles have improved drastically. The possible market for jute geotextiles is bigger; though it is not yet being completely utilized. In order to get benefits of the prospects presented, the jute industries must carry a more market driven approach, reacting to the requirement of customers and must develop standards for its products.

Flax/coir

Coir is a natural insulation material produced from flax fibers, intertwined together into non-woven matting, which can then be set in lofts or put into wall cavities. Coir geotextiles are applied in areas of erosion control, soil conservation, and other civil and bioengineering applications. It also has the appropriate strength and toughness to protect the slopes from erosion while permitting vegetation to flourish. They can dissolve the energy of flowing water and absorb the extra solar radiation.

Coconut (Coir) Matting

Used or recycled goods of the coconut fibers from the post industrial waste can also be applied as the economical applicators. It gives low impact and reasonable result to the problems of soil erosion and land sliding on manmade slopes such as motorway and railway embankments.

Cotton

Cotton is mainly made from old clothes in the form recycled cotton or from the post consumer waste stream, is available in a broad variety of colorways, each having the feature of speckling due to the lack of discrimination during the recycling and sorting stages of production.

Hemp

These are available in a broad woven variety.

Straw

Produced by a mixer of straw and a loosely woven net of biodegradable string, gives a minimal influence and realistic answer to the problems of soil erosion and land sliding on manmade slopes such as motorway and railway embankments.

Kevlar

Woven Kevlar textiles possess the structural dynamics and works better than steel, but with a fraction of its weight. Whether it is working in a plant, or handling sharp edge materials kelwar bring together high strength (5 times stronger than steel) with light weight, and comfort with protection. Kevlar is also made at low temperatures. They are applied as the reinforcement of cement concrete in the form of chopped fibers both for ordinary and autoclave cure types. Kevlar can also be used with other materials as a protective coating.

Polyester

Made from the post consumer waste such as bottles, fabrics, etc. in the composition of polyester ethylene terephthalate, and because of its superior strength and elasticity it is applicable to numbers of geotechnical applications.

Polypropylene

Polypropylene is a famous alternative for geo-grids or geo-matrices, as it is strong and chemically static. Polypropylene is accepted to carry out poor long-term creep behavior but is economical and light in weight.

Phenolic/jute composite

This composite is a strong and abundantly durable, made by the mixing of jute fibers with a phenol based resin binder. Bio-composites such as this one give substitute of making durable, high performance materials whilst applying as few non-renewable as probable. This material is extensively applicable within a range of furniture design applications.

Besides these, many other types of materials may be applied to make geotextiles, according to its applications. Geotextiles are more and more applied in civil engineering works and so their production has new openings to the textile industries. New and various types of geotextiles are made worldwide and are applied in a variety of applications. The majority of geo-fabrics are made from synthetic materials, but there are few uses that require biodegradable, natural materials such as coir or jute. Unlike synthetics, they can absorb and store moisture, their natural flexibility permits them to match directly to soil profile and their bulk provides great productive cover/weight ratio. As natural material, these are well-matched with surrounding vegetation and are easily available with an economical rate. Natural fibers are available in a large quantity in India. They are comparatively economical and can give a cost-effective solution to short span projects. In the coming years, all these factors show bright prospects for geotextiles worldwide.