Geotextile is a kind of geosynthetic product, it is used in various engineering projects. The main functions of geotextiles are filtration, drainage, separation, reinforcement protection, and erosion control. Geotextile has been used as the sole method of providing filtration and drainage functions for some dam embankments constructed in many countries.
Geosynthetics have been used in dam construction for over 45 years, and are currently being used at an ever-increasing rate in a variety of applications. Geosynthetics are not new for dam construction, and in fact, are considered a reliable and durable civil engineering material with proven performance in many exposed and buried applications. Geosynthetics are used in dam construction not only because they may be the only practicable choice for a specific application but also because they provide a viable and durable economic alternative to other types of conventional civil engineering materials.
A geotextile will perform a filtration function if it allows liquid (water) to pass while controlling the soil. The geotextile thus must be located between the soil being retained and the open drain material, nonwoven needle-punched geotextiles are used.
The geotextile will have a separation function if the geotextile is located between two dissimilar soils or between soil and a man-made material and if the geotextile prevents the mixing of the two dissimilar materials. All types of geotextiles and composites that have the smallest strength requirements can perform this function.
The types of geotextiles that follow the definition are the nonwoven, woven, and knitted fabrics which again are typical fabrics of the textile industry today. Geotextiles, yet, are manufactured in plants that are now devoted to the technical geotextile industry segment and thus are engineered for today’s demanding applications in geotechnical engineering. Thus the term “geotextile” is not new but in fact, describes the general functions of “fabrics” used to improve soils or soil conditions. Geotextile polymers are polypropylene (PP), and polyester (PET) with some geotextiles (nonwovens) using combinations of polymers. Geotextile structures are comprised of the following:
Nonwoven geotextiles
Geotextiles are formed with continuous or short fibers arranged in random directions and then bonded together into a planar structure which can include the following:
Nonwoven geotextiles
Needle punched
Continuous Filament Fiber
Staple Fiber (short fibers)
Nonwoven Heat Set
Continuous Filament Fiber
Woven geotextiles
Woven Geotextiles are composed of two sets of parallel yarns or tapes interlaced to form a planar structure which can include the following:
Multifilament woven
Monofilament woven
Slit Film woven
Fibrillated woven
Polypropylene (PP) fiber is a semi-crystalline thermoplastic olefin produced by polymerizing propylene monomers in the presence of a catalyst. Two types of polypropylene are the homopolymers and the copolymers. The more rigid homopolymers are used in fiber production. Polypropylene homopolymers for geotextile production are designed to meet both the stringent processing and final end-use strength and durability requirements. Polypropylene fiber is produced by melt spinning the molten polymer, followed by stretching to orient the fiber molecules. Special additives including antioxidant packages and thermal stabilizers and UV packages are used to protect against aging. A life expectancy of the smallest of 200 years can be expected from stabilized and protected polypropylene geotextile fibers in buried applications
Polyester, generally known as polyethylene terephthalate (PET), is a manufactured fiber produced by polymerizing ethylene glycol with dimethyl terephthalate or terephthalic acid. Various additive packages are used to increase the speed of polymerization as well as antioxidants and thermal stabilizers to reduce degradation during production and aging. stabilized polyester in a covered environment will have a very long life expectancy. Polyester fibers have high strength and are resistant to shrinking and stretching (creep). Polyester fiber must be protected from aggressive alkaline environments.
Nonwoven fiber types as discussed above are either continuous filament or staple filament. The continuous filament process is also referred to as the spun-bonded process where fabric is formed by filaments that have been extruded, drawn, and then laid in a random mass on a continuous moving belt. Staple filaments are short lengths of continuous fiber that are placed in a random orientation mass on a moving belt. Both processes for nonwoven geotextiles are then bonded or stabilized as a web by thermal (heat set or melt of fibers) or mechanical needle punching. The needle punching process interlocks fibers by driving a large needle loom with thousands of barbed needles down and up through the continuous or staple fiber web. The resulting entanglement stabilizes the web.
Woven geotextiles are made on conventional mechanical textile weaving machines into a variety of fabric weaves. The pattern of the weave is determined by the sequence in which the warp (long or machine direction) filaments or yarns are threaded into the weaving loom and encapsulate the weft (cross-machine or short direction) yarns. The various types of weaves used in the production of woven geotextiles are simple and cost-effective and thus most woven geotextile fabric structures fall into the plain weave category. The woven final product is wound onto rolls off of the weaving loom. The fiber type or elements can be single monofilaments, multifilaments, tape yarn, or flat tapes. The resulting structures are 1 mm in thickness with a regular distribution of pore size or mesh openings.
It must be emphasized that geotextiles buried in embankment dams are protected from exposure to the elements, and from too many environmental degradation mechanisms including damaging effects of UV, high temperatures or even temperature fluctuation, and accelerated oxidation due to exposure (thermo-oxidation and photo-oxidation). Hydrolysis degradation (chemical decomposition by addition of water) is associated with extremes of pH which are usually not a problem unless immediate contact with concrete is anticipated (alkaline environment) or the dam is a tailings dam or contaminated water containment dam that may be exposed to acidic impoundment solutions, and then this only affects PET geotextiles. Chemical and radioactive degradation are usually associated with waste containment applications and are not a consideration in buried soil environments such as internal to a dam. Biological degradation is also not generally associated with geotextiles other than by biological clogging which will occur in some soil environments (i.e. iron ochre) but which does not degrade the polymer.
