Geotextiles and it’s Types


Geotextiles is a synthetic permeable textile material applied with soil, rock, or any other geotechnical engineering related material. Textiles were first applied to roadways in the days of the Pharaohs. Even they struggled with unstable soils which rutted or washed away. They found that natural fibers, fabrics or vegetation improved road quality when mixed
with soils, particularly unstable soils. Only recently, however, have textiles been used and evaluated for modern road construction. This fact sheet clarifies the confusion over terms and definitions of geotextiles, and discusses their common roadway and erosion control applications. In the 1920’s the state of South Carolina used a cotton textile to reinforce the underlying materials on a road with poor quality soils. Evaluation several years later found the textile in good workable condition. They continued their work in the area of reinforcement and subsequently concluded that  combining cotton and asphalt materials during construction reduced cracking, raveling, and failure or the pavement and the base course. When synthetic fibers became more available in the 1960’s, textiles were considered more seriously for roadway construction and maintenance. As these new synthetic fabrics evolved, there was confusion over terms and definitions. Textiles and membranes now have reasonably well accepted definitions in the construction industry. 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. 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. Geotextiles are existed with more than fifty year. Though, the development of market and research work put in to practice in early 1960s. 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 2012) 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 technicaltextile market. Furthermore, this sector with low unit values in small numbers gives a large margin. 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 geotextiles 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.

Geo-fibers are usually polypropylene fibers blended into soils to create an ideal reinforcement system for the repair of slope failures, reinforcement of pavement subgrades, foundation stabilization, and improvement of retaining wall backfill. By synergistically meshing with the soil already on site, geofibers help create a soil reinforcement system with dramatically improved engineering properties.

image

Figure 2 Geofiber

Types of Geotextiles

  • Geomembranes

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 or bituminous. 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. Geomembranes are commonly used as barriers in waste containment facilities and landfills due to various benefits associated with their use and because of regulatory requirements.

Geomembrane are also increasingly being used in reservoirs, ponds, lined canals and other geotechnical projects. Geotechnical engineers often characterize the shearing resistance along interface between geomembranes and soils using results from interface direct shear tests. The results of these tests are used in an analysis of stability against sliding along the given interface. Interface shear testing between soil and geosynthetics has now become an essential part of the design process in geotechnical and geo-environmental engineering.

Geomembranes are “impervious” thin sheets of rubber or polymeric material used primarily for linings and covers of liquid or solid waste containment facilities. Geomembranes represent the largest category (by cost), of geosynthetics products used in civil engineering applications. The growth in the use of geomembranes can be attributed to the various benefits associated with their application, their relative economy and increasingly stringent environmental regulations. The mechanism of diffusion in geomembrane is on molecular scale which is different from other porous media. Water molecules diffuse through narrow spaces between polymer molecular chains. Geomembranes cannot be regarded as totally impermeable as some amount of diffusion permeation is observed in geomembranes. A typical thermoplastic geomembrane will have diffusion permeability of the order of 10-11 to 10-13 cm/s. Because of their extremely low permeability, their primary function is as a liquid or vapour barriers.

Calendered Geomembranes:

Calendered geomembranes are formed by working and flattening a molten viscous formulation between counterrotating rollers. Polyvinyl chloride (PVC), chlorosulfonated polyethylene (CSPE), chlorinated polyethylene (CPE), and, more recently, polypropylene (PP) are the most common calendered geomembranes. Specialty ethylene interpolymer alloy (EIA) geomembranes are used for unique applications. In most cases these engineered films are supported by a textile that provides tensile strength and enhances tear and puncture resistance.

Extruded Geomembranes:

Extruded geomembranes are manufactured by melting polymer resin, or chips, and forcing the molten polymer through a die using a screw extruder. The sheet is formed either by a flat horizontal die or through a vertically oriented circular die to form either a flat wide sheet advanced on a conveyor belt, or cylindrical tube of “blown film”, filled with air which is collapsed and pulled by nip rollers mounted high above the die. Blown film geomembranes must be slit prior to wind-up. Common extruded geomembranes include high-density polyethylene (HDPE) and various lower density, or very flexible, polyethylenes (VFPE). Polypropylene (PP) is a relatively new type of extruded (as well as calendered) geomembrane. Variations in the manufacturing of geomembranes include texturing to enhance the interface friction between the geomembrane and adjacent soils or other geosynthetics; coextruding different polymers into a single sheet to provide enhanced durability; and the availability of multiple thicknesses and sheet sizes. Geomembranes are thin, two-dimensional sheets of material with very low permeability. This makes them ideal for forming waterproof or gas proof barriers between adjacent bodies of soil or soil and fluid. Some of their potential applications include sealing against fluid percolation along the coasts, river banks, reservoirs and in water storage. They are also used as buffers against pollutants. The manufacturing of geomembranes begins with the production of raw materials. These are polymer resin, plasticizer accelerators or retarders, filters, and processing aids. The raw materials are blended together and compounded before being extruded in sheet or cylindrical form. Extruders both melt the above materials and homogenize them into a consistent fluid mass in a partial vacuum. The vacuum eliminates air bubbles in the final product.

  • 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. Geogrids are single or multi-layer materials usually made from extruding and stretching high-density polyethylene or polypropylene or by weaving or knitting and coating high tenacity polyester yarns. The resulting grid structure possesses large openings (called apertures) that enhance interaction with the soil or aggregate.

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 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. Geonets are made of stacked, criss-crossing polymer strands that provide in-plane drainage. Nearly all geonets are made of polyethylene. The molten polymer is extruded through slits in counter-rotating dies, forming a matrix, or “net” of closely spaced “stacked” strands. Two layers of strands are called “bi-planar”. Three layers are called “tri-planar”.

Geonets are the most recently introduced members of the geosynthetic family. They are grid-like materials, however, distinct, from geogrids by virtue of their function. They do have considerable strength but are used mostly for drainage purposes. All geonets are made of polyethylene. The specific gravity of most geonets is in the range of 0.935 to 0.942. The only other materials in geonets are carbon black and a processing package. In manufacturing, the ingredients are mixed and passed through an extruder, which injects the melt into a die with slotted counter-rotating segments. Over these, the melt flows at angles forming discrete ribs in two planes. As pressure forces the semi-solid mass forward, it is pushed over an increasing diameter core, which forces the ribs apart and opens the net. Diamond-shaped apertures are formed that are typically 12mm long by 8mm wide. Geonets are typically 5.0 to 7.2mm thick. Thickness is a key factor in determining drainage capability. Adding a foam agent to the ingredients can increase thickness of geonets.

  • 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.

Advertisements

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s