P.Dhanapal, Department of Textile Technology, Kumaraguru college of TechnologyA 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 bonded
6) Nonwoven continuous filament needle-punched
7) Nonwoven staple needle-punched
8) Nonwoven resin bonded
Modern geotextiles are usually made from synthetic polymers- polypropylenes, polyesters, polyethylenes, and polyamides - which do not decay under biological and chemical processes. This makes them useful in road construction and maintenance.
The makeup of the fabrics determines their best application, so it is important to understand their characteristics.
The nonwoven fabric, which looks like a felt fabric, is an arrangement of fibers 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 fibers 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.
1) Geo Textiles in Road Industry
In the road industry there are four primary uses for geotextiles:
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 subgrade 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 subgrade and the subbase and the permeability of the geotextile.
Required properties for separation:
3) 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.
4) 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.
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.5) 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.
6) 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.
7) 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.
Textiles are not only clothing the human body but also our mother land in order to protect her. Extensive awareness should be created among the people about the application of geotextiles.To explore the potential of geotextile more researches are needed in this field.