Geotextile And Its Application 3i2k5e

GEOTEXTILE AND ITS APPLICATION TEJU KUMAR N & MADANA GOPALA REDDY M, 8TH SEM, CIVIL ENGINEERING

SRI SIDDHARTHA INSTITUE OF TECHNOLOGY, TUMKUR

1. INTRODUCTION GEOTEXTILES Geotextiles form one of the two largest groups of geosynthetic materials. They are indeed textiles in the traditional sense, but consist of synthetic fibers (all are polymer-based) rather than natural ones such as cotton, wool, jute or silk. Thus, biodegradation and subsequent short lifetime is not a problem. These synthetic fibers are made into flexible, porous fabrics by standard weaving machinery or they are matted together in a random nonwoven manner. Some are also knitted. The major point is that geotextiles are porous to liquid flow across their manufactured plane and also within their thickness, but to widely varying degree. There are at least 100 specific application areas for geotextiles that have been developed; however, the fabric always performs at least one of four discrete functions; separation, reinforcement, filtration and/or drainage.

2. HISTORY INITIAL DEVELOPMENTS From the time immemorial people have been aware that tree roots strengthen soil. People in ancient times used bamboo, wood and other materials along with sand and mixtures of mud and clay in house construction. The use of logs or tree trunks of uniform sizes, fixed together to form a mattress for crossing marshy areas, is quite old. Inclusions of different sorts mixed with soil have been used for thousands of years. They were used in roadway construction in Roman days to stabilize roadways and their edges. These early attempts were made of natural fibres, fabrics or vegetation mixed with soil to improve road quality, particularly when roads were built on unstable soil. They were also used to build steep slopes as with several pyramids in Egypt and walls as well. A fundamental problem with using natural materials (wood, cotton, etc.) in a buried environment is the biodegradation that occurs from microorganisms in the soil. With the advent of polymers in the middle of the 20th Century a much more stable material became available. When properly formulated, lifetimes of centuries can be predicted even for harsh environmental conditions.

3. FUNCTIONS OF GEOTEXTILES Geotextiles are generally designed for a particular application by considering the primary function that can be provided. SEPARATION is the placement of a flexible geosynthetic material, like a porous geotextile, between dissimilar materials so that the integrity and functioning of both materials can remain intact or even be improved. Paved roads, unpaved roads, and railroad bases are common applications. Also, the use of thick nonwoven geotextiles for cushioning and protection of geomembranes is in this category. In addition, for most applications of geofoam, separation is the major function.

REINFORCEMENT is the synergistic improvement of a total system’s strength created by the introduction of a geotextile or a geogrid (both of which are good in tension) into a soil (that is good in compression, but poor in tension) or other disted and separated material. Applications of this function are in mechanically stabilized and retained earth walls and steep soil slopes; they can be combined with masonry facings to create vertical retaining walls. Also involved is the application of basal reinforcement over soft soils and over deep foundations for embankments and heavy surface loadings. Stiff polymer geogrids do not have to be held in tension to provide soil reinforcement, unlike geotextiles. A stiff geogrid interlocks with the aggregate particles and the reinforcement mechanism is one of confinement of the aggregate. The resulting mechanically stabilized aggregate layer exhibits improved loadbearing performance. Stiff polymer geogrids, with rectangular or triangular apertures, are also increasingly specified in unpaved and paved roadways, load platforms and railway ballast, where the improved loadbearing characteristics significantly reduce the requirements for high quality, imported aggregate fills, thus reducing the carbon footprint of the construction.

FILTRATION is the equilibrium soil-to-geotextile interaction that allows for adequate liquid flow without soil loss, across the plane of the geotextile over a service lifetime compatible with the application under consideration. Filtration applications are highway under drain systems, retaining wall drainage, landfill leachate collection systems, as silt fences and curtains, and as flexible forms for bags, tubes and containers.

DRAINAGE is the equilibrium soil-to-geosynthetic system that allows for adequate liquid flow without soil loss, within the plane of the geosynthetic over a service lifetime compatible with the application under consideration. Geopipe highlights this function, and also geonets, geocomposites and (to a lesser extent) geotextiles. Drainage applications for these different geosynthetics are retaining walls, sport fields, dams, canals, reservoirs, and capillary breaks. Also to be noted is that sheet, edge and wick drains are geocomposites used for various soil and rock drainage situations.

4. TYPES OF GEOTEXTILES 1. WOVEN GEO TEXTILES: are produced by weaving with two sets of spun yarn at right angles to each other. 2. NON WOVEN GEO TEXTILE: are made from extruded continuous filaments or staple fibre webs which are bonded by mechanical or thermal means. 3. KNITTED GEO TEXTILE: are produced by interlooping the two sets of yarns.

5. COIR: A GEOTEXTILE Coir fibre is obtained from the fibrous husk covering the inner shell of the coconut fruit and is the raw material for the coir Industry. The coir fibre is one of the hardest natural fibres available Because of its high content of lignin; coir is much more advantageous in different Application for erosion control, reinforcement and stabilization of soil and is preferred to any other natural fibers. The fibers are hygroscopic, with a moisture content of 10% to 12% at 65% humidity and 22% to 55% at 95% relative humidity. In India, it is estimated that 27% of land area is subject to soil erosion leading to a loss of about 6000 million M.Ts. of topsoil annually. The consequences of such large scale soil erosion are causing serious concern to the vary question of sustainable development .Geo-textiles as a media for soil reinforcement has been known from early civilizations. Products made out of coir, like meshes and nettings, needled felts and pads, erosion control blankets and mulch blankets, geo rolls vegetation fascines, geo cushions and geo beds, braided ropes, anti weed blankets etc. can be effectively used enabling speedy growth of vegetation. It is being used in slope stabilisation, erosion control treatment, sub-base layer in road pavement, in drain works and similar soil bio engineering applications. The coir geo-textiles can be customised to specific requirements according to the topographical conditions. Being biodegradable and eco friendly it is an excellent substitute for geo-synthetics. The advantage of coir geo textiles are:

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The high tensile strength of coir which protects steep surface from heavy flows and debris movement.

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Five to ten years longevity that allows for full plant and soil establishment, Natural invasion and land

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Coir functions as a soil amendment because it is 100% natural and biodegradable

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Water absorbent coir acts as a mulch on the surface and as a wick in the soil mantle

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It provides an excellent micro climate for plant establishment, natural invasion and balanced healthy growth

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Coir re-vegetation meshes encourage the restoration of terrestrial and aquatic riparian habitat

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Coir geo-textile as whole are environmentally responsible and aesthetically Pleasing

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Can be customised to specific requirements according to the topographical conditions

The economic feasibility factor of geo-textiles is related to the cost of material, installation cost as well as its impact on eco system and aesthetics. Taking those factors into consideration the coir geo-textiles has established as a very competitive and suitable substitute for synthetic geo-textile.

5.1 ADVANTAGES OF COIR •

100% natural

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Adds organic material to soil

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Promotes vegetative growth

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Easy to install

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Versatile

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Bio-degradable

6. APPLICATION OF COIR IN GEOTEXTILE: 6.1 COIR IN PREVENSION OF SOIL EROSION Riverbank erosion problem is becoming acute in many alluvial rivers in India. Proper remedial measures need to be carried out, to prevent such bank erosion. The embankment slopes suffer extensive damages due to erosion from rainfall and flowing water. Gully erosion, Formation of Rills, Sheet Erosion and Toe Erosion are some of the forms of these damages. Controlling the erosion of fertile layer of topsoil is one of the mankind’s foremost problems. Erosion consists of the loosing and transportation of soil particles. A heavy thunderstorm will throw into air up to 250 tons per hectare of topsoil and flowing water which can no longer be absorbed by the soil causes rills and gullies. The land and vegetation disturbances due to deforestation, mining and construction create conditions for accelerated erosion. Rainfall, agricultural and forestry disturbances cause India to loose 6000 million tons of precious topsoil annually (27% of India’s land area is subjected to erosion). MECHANISM OF EROSION CONTROL BY VEGETATION GROWTH: The presence of netting on the slope controls the surface erosion in the following ways. (a) The surface run-off gets divided into a number of small paths due to the numerous obstructions caused by the presence of netting. As a result, the overall damaging impact of flowing water is reduced. (b) The soil and seeds are thereby preserved in place providing increased chances for germination and growth of vegetation. The slope once covered with vegetation prevents the erosion in a number of ways. The vegetation cover on the slope reduces the impact of falling rain drops and retards the velocity of running water. The root network that penetrates deep into the soil, it binds the soil particles together to improve the resistance to erosion and thereby improves the stability against failure of the slope. TECHNIQUE OF SURFACE CONTROL USING COIR NETTING. The slope is first leveled to remove any unevenness present like deep irregular gullies, projecting stones. Earth work excavation and gravel backing to be done, wherever necessary. A suitable fertilizer is mixed with the soil at the rate of 0.5 kg/10 sq. mtrs. Seeds of selected variety of deep rooted and quick growing grass are then spread over the slopes. Half the quantity of seeds is spread prior to covering of the slopes with netting and the other half subsequent to laying of the netting. The rolls of the Coir Netting are spread out of the slope and each roll is given overlapping of 4” with the adjacent one, and anchored firmly into the ground by steel staples.

The above full-scale field trail establishes the effectiveness of coir netting for erosion control. The process is not only simple and quick but also very economical, saving more than 50% in cost compared to conventional gravel lining process. The colour of the coir fibre is not a criterion for erosion control application. This is sure to give a fillip to the brown coir sector considering the abundant potential that lay untapped in the field of Geo-textiles.

6.2 COIR BLANKET FOR SOIL CONSOLIDATION The unique qualities of the coir contribute liberally to the functions of the blanket in different capacities and measures, as under. The Coir Needled felt laid as blanket over the vertical drains allows the pore water, which gets collected and accumulated through and into the drain, to move freely to the sides. The Needled felt here acts as separator, filter, and filter reinforcement and facilities drainage during the function. While performing as a separator, the Coir Needled felt at the same item will act as a filter allowing water to freely through or into the plane. Again, it tends to confine the ing aggregate beneath the pressure aggregates able to retain a degree of reinforcement within itself. The installed Coir Felt permits the water entering to be transmitted laterally, away from the areas of loading also. As a barrier, the blanket prevents the inter mixing of materials from either sides also.

6.3 UNREINFORCED EMBANKMENT FAILURE AND USES OF GEOSYNTHETICS AS REINFORCEMENT. In such problems, geosynthetics can be effectively used to 1) Reduce soft soils displacements due to low bearing capacity of soft soils; Geosynthetics Soft ground

2) Prevent overall failure of the embankment and soft foundation soil; and

3) Prevent sliding failure along the geosynthetics surface.

The stability level of a reinforced embankment on soft soil can be evaluated by the definition of safety factors (Fs): • For overall stability

Where MD: soil driving moment MR: soil resisting moment

ΔMR: geosynthetic moment contribution against failure • For stability against sliding failure

PA: active thrust from the fill (from active earth pressures) PR: friction force along the fill-reinforcement interface The efficiency of geosynthetics as reinforcements of embankments on soft soils can be visualized by the following figures.

6.4 GEOTEXTILES IN UNPAVED ROADS Geosynthetics can be effectively used to reinforce unpaved roads and working platforms on soft soils. If well specified, a geosynthetic can have one or more of the following functions: separation, reinforcement and drainage. Geotextiles and geogrids are the most commonly used materials in such works. Compared to the unreinforced unpaved road, the presence of geosynthetic reinforcement can provide the following benefits: • Reduction of fill thickness; • Separates aggregate from soft soil if a geotextile is used; • Increases soft soil bearing capacity; • Reduces fill lateral deformation; • Generates a more favorable stress distribution; • Widens the spreading of vertical stress increments;

• Reduces vertical deformation due to membrane effect; • Increases the lifetime of the road; • Requires less periodical maintenance; • Reduces construction and operational costs of the road.

Typical degradation mechanisms in unreinforced unpaved roads on soft soils

Influence of geosynthetic reinforcement on unpaved road behaviour As the depth of the ruts increase the deformed shape of the geosynthetic provides further reinforcement due to the membrane effect. The vertical component of the tensile force in the reinforcement reduces further vertical deformation of the fill. Several researches in the literature have shown that in a reinforced road a given rut depth will be reached for a number of load repetitions (traffic intensity) larger than in the unreinforced case. This will yield to a greater life time and less periodical surface maintenance. A draining reinforcement material will also accelerate soft soil consolidation, increasing its strength. Drainage of the soft soil can be achieved by using a geotextile, a geogrid and a geotextile or a geocomposite as reinforcement. The stabilization of the top region of the soft foundation will be beneficial if the road is to be paved in the future reducing construction costs and minimizing pavement deformations.

Design methods are available in the literature, including simple ones involving the use of charts for preliminary analyses. These methods require conventional soil and reinforcement parameters for design purposes under routine conditions. Some design charts have also been developed by some geosynthetics manufacturers specifically for preliminary design using their products.

7. ADVANTAGES 

The manufactured quality control of geosynthetics in a controlled factory environment is a great advantage over outdoor soil and rock construction. Most factories are ISO 9000 certified and have their own in-house quality programs as well.

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The thinness of geosynthetics versus their natural soil counterpart is an advantage insofar as light weight on the subgrade, less airspace used, and avoidance of quarried sand, gravel, and clay soil materials.

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The ease of geosynthetic installation is significant in comparison to thick soil layers (sands, gravels, or clays) requiring large earthmoving equipment.

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Published standards (test methods, guides, and specifications) are well advanced in standards-setting organizations like ISO, ASTM, and GSI.

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Design methods are currently available in that many universities are teaching stand-alone courses in geosynthetics or have integrated geosynthetics in traditional geotechnical, geoenvironmental, and hydraulic engineering courses.

8. DISADVANTAGES 

Long-term performance of the particular formulated resin being used to make the geosynthetic must be assured by using proper additives including antioxidants, ultraviolet screeners, and fillers.

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Clogging of geotextiles, geonets, geopipe and/or geocomposites is a challenging design for certain soil types or unusual situations. For example, loess soils, fine cohesionless silts, highly turbid liquids, and microorganism laden liquids (farm runoff) are troublesome and generally require specialized testing evaluations.

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Handling, storage, and installation must be assured by careful quality control and quality assurance of which much as been written.

9. CONCLUSIONS The use of geosynthetics in soil reinforcement and other applications is widely practised in western countries. If the potential of these materials is rightly understood,the use of techniques employing geosynthetics is bound to increase significantly in many developing countries. While the reinforcement function is possible using polymeric reinforcement in the form of grids, rods and strips, functions such as separation, filtration, and drainage and moisture barrier are possible only using geosynthetics.

10. REFERENCES 1. An Introduction to Soil Reinforcement and Geosynthetics by G L Sivakumar Babu. 2. Ground Improvement Techniques by Purushotam Raj. 3. International Geosynthetics Society. 4. Wikipedia.com 5. Central Institute of Coir Technology. 6. National Coir Research and Management Institute.