of technical textiles One of the biggest usage areas is geo-textiles. There are many uses in soil stabilization, erosion control, moisture barriers for concrete and asphalt, and coating materials used in artificial pond-pool type structures.
When used for soil stabilization and erosion control, geotextiles spread between layers, creating buffer zones and making the soil resistant to slipping. In this way, the movements of the soil layers are prevented, but sufficient environment is provided for possible water currents. Geotextiles prevent slipping as they spread the stresses in the ground over a large area. Because of these features, they are frequently used in the construction of structures such as dams, dams, water channels, sewer systems, etc. In asphalt road construction, geotextiles are placed on top of the soil and stone layers, just below the asphalt layer. In this way, the stresses are equalized. This system prevents the asphalt from breaking and reduces the amount of asphalt required to stabilize the road surface.
The desired properties of geotextiles are to be resistant to possible damages caused by insects and micro-organisms, to be unaffected by temperature changes during application and use, to be resistant to possible chemicals, to be resistant to light, etc. are features. It is also desirable that they be of sufficient strength according to their use. Often they are also expected to have special structures (very thin and strong, etc.). They are usually in the form of non-woven surfaces. They are also used as woven fabrics in some applications.
Various woven geotextiles are used to hold the walls together in areas with high earthquake risk.
Their use in agriculture is more related to erosion control. Composites of hides, bush and straw have been used for thousands of years to reinforce soft soils. Although theoretically doing the same job, modern geotextiles have standard and consistent properties. With the various textile polymers developed, geotextile science has found new application areas.
In the 1960s and early 1970s, textiles were used to cover canals and to prevent mud and mud from clogging the canals. Similarly, ways of using textiles under the small exit roads built on very soft wet soils have been tried. It has been observed that these applications increase the life and performance of the roads. At the same time, the first studies began to take place on the laying of textiles on the beach in order to prevent erosion caused by wave action.
In the last 20 years of the 20th century, the use of geotextiles spread geographically all over the world and the amount of use increased considerably. It is expected that the use of geotextiles will continue to increase in the 21st century.
In geotextile, besides fibers, various fabric constructions have been used quite a lot. The development of synthetic fibers has also increased the performance of geotextiles. In some cases, composite structures made of textiles and metals have also been used.
It can be considered that the “first generation of geotextiles are textiles (carpets or industrial sacks) produced for other purposes, but diverted and used for geo-technical purposes. The second generation of geotextiles has been produced by manufacturers who choose specific textiles suitable for geotechnical purposes but use conventional production techniques. Third generation textiles are specially produced for geo-technical application purposes, examples of which are DSF, DOS and composite products.
The establishment of the International Geotextile Society in 1978 provided the coordination and appropriate approach for the international development of geotextile design and use.
Geotextiles are part of civil engineering membranes called geosynthetics. They vary in their construction and appearance.
However, they are usually made from a limited number of polymers (polypropylene, polyethylene and polyester) and mostly have five basic types:
- Weaving,
- heat bonded
- fixed with pins,
- Knitting
- Direct soil mixed fibres.
The physical properties of the products in these various groups vary according to their strength, which reaches up to 2000 kNm-1. However, it is commonly between 10 and 200 kNm-1. Their elongation can exceed 100%, but the usable range for engineers is between 3 and 10%. Similarly, the filtration potential and permeability of different geotextiles vary considerably.
Geotextiles are used in civil engineering to support the vertical and vertical edges of the soil, to build solid foundations for temporary and permanent roads and highways, to lay ground channels, thereby filtering the soil itself and preventing the soil from filling channels, and preventing erosion behind rocks and stones on riverbanks and beaches. Geotextiles have been in development since the mid-1970s, but the development of knitted and composite fabrics has reinvigorated efforts to improve textile construction. Better physical properties can be achieved by using more than one fabric and utilizing the best properties of each fabric.
geosynthetics
Membranes used in civil engineering, in or in contact with soil “geosynthetics” are named. The term includes permeable textiles, plastic grids, endless and staple fibers and impermeable membranes. Textiles are the first products in this field. While other products were added, textiles remained the most important. Grids consist of perforated and stretched plastic sheets, meshes, melt-extruded polymers. None of these can be categorized as textiles. Geozars are continuous plates made of impermeable plastics, which are not textiles. Geosynthetic fields, which are much more difficult to categorize, are the situations where tight staple and endless fibers are directly mixed with the soil. These are polymer textile fibers and therefore they are included in the definition of geotextile.
Geotextile Types
Geotextiles are generally divided into five categories.
These:
- weavings,
- Heat bonded nonwoven textiles,
- Nonwoven textiles fixed by needling,
- knits
- They are fiber/soil mixtures.
Woven fabrics
It is produced on looms that give them a smooth construction, however, it differs in terms of weaving construction with the fibers that make up it. They have a surprisingly wide range of applications and are used in lighter weights as soil separators, filters and erosion control textiles. Heavy weight ones are used as soil supporters in steep embankments and earthen walls; even heavier ones are used to support embankments built on soft soils.
The positive properties of woven structures in terms of support are that the tension is absorbed by the warp and weft threads, and consequently the fibers, without being subjected to too much mechanical elongation. This gives them a relatively high modulus or stiffness.
Heat-bonded nonwoven textiles
It is generally obtained by randomly laying fine endless fibers on a moving conveyor belt and passing them between heating rollers. These fabrics gain their strength and the properties of holding the fibers together with each other as a result of the partial melting of the fibers between the hot rollers and a relatively thin textile layer is obtained.
Nonwoven fabrics fixed by needling
It is produced by fixing many ends of cheesecloth formed from staple fibers and filaments by needles with notched needles. The fabrics get their mechanical bonding properties from the fiber tangles caused by the hooks on the needles. These fabrics are similar to wool felts.
Knitted fabrics used in geotextiles
It is limited to warp knitted textiles and is produced specifically for the purpose. Fine filter fabrics, medium mesh screens and large diameter soil support grids are produced in warp knitting machines. However, products used for soil reinforcement and dam support purposes have been found to be more cost effective.
Basic Polymers Forming Geotextile Fibers
The two most commonly used polymers in the production of geotextiles are polypropylene and polyethylene.
However, when high strength is required, the use of polyester is also inevitable. There are other high-strength polymers on the market, but geotextiles must be produced in large quantities (some polymers are not available in large volumes) and economically (special polymers are very expensive). In terms of cost versus performance, polyester is today's optimum. Polypropylene and polyethylene compete to be the most chemically resistant.
The polymers produced and used for use in geotextiles are not chemically pure..
For example, colorless, transparent raw polyethylene is highly susceptible to degradation by light. It usually contains carbon black as an ultraviolet (UV) light stabilizer, as it cannot be used in geotextiles in this state. In this black form, it is the most lightfast polymer.
In addition, the possibilities of testing geotextile polymers in a real-like manner are limited. Publications and authorities can provide accelerated laboratory results with xenon UV exposure, high temperature degradation testing and similar tests, however, these include additional degradation factors such as biological attack or synergetic reactions that may occur during actual use. Accelerated laboratory tests, if used for grading purposes, may present difficulties as they can be optimistic at some points and pessimistic at others.
Polyamide Although it is a general fiber former and textile material, it is rarely used in geotextiles. Because its cost and performance is worse than polyester.
For example, in some woven materials, it is used as a filling in the weft direction, when its properties are not very critical. Its main feature is its resistance to abrasion, but it has not been very popular for geosynthetic use because it softens when exposed to water.
Polyvinylidene chloride fiber is used in one or two products in Japan and the United States, but not in Europe.
Important Properties of Geotextiles
The three main characteristics required and specified for a geotextile are:
Mechanical behavior
Filtration ability
Chemical
It is resistance.
These are the properties that provide the required working effect and are developed from the combination of the physical forms of the polymer fibers, their textile constructions and the polymer chemical properties.
For example, the mechanical behavior of a geotextile depends on the type of polymer from which it is made, as well as on the smoothness and orientation of the fibers. Moreover The chemical resistance of a geotextile depends on the size and chemical composition of the fibers in the fabric.. Thin fibers with a large specific surface area undergo chemical damage faster than thicker fibers produced from the same polymer.
Mechanical behaviors include the ability of a textile to do work in a stressed environment and to resist damage in a harsh environment. Generally, tense environments are known in advance and the textile is selected based on numerical criteria that can withstand the expected tension and its ability to absorb tensions by not stretching more than a predetermined amount during the anticipated usage period.
The ability to do work mainly depends on the stiffness of the textile under tension and its resistance to extension over time under any given load. The ability to resist damage is complex and is a function of the fabric's construction, which determines how the fiber resists breaking and how tensions are concentrated and released. In practical terms, geotextiles are produced in composite form using a protective construction type to reduce damage to a working element.
For example, a thick nonwoven fabric can be combined with a woven fabric. Woven fabric performs its duty of strength, while nonwoven acts as a damage prevention cushion.
Many factors affect the filtration performance of a geotextile. In order to understand this, it is necessary to understand that the function of textile is not really like a filter. In general, filters remove particles suspended in a liquid. Examples of these are dust filters or water filters in air conditioners used to remove suspended dirt.
The opposite is true for geotextile filters. The function of geotextile is to keep a freshly prepared soil surface intact and to allow water to seep through this surface and through the textile without damaging the surface. If water is allowed to flow through the textile-soil interface with suspended particles, the textile will not be able to perform its functions by clogging. In practice, soil with a textile tends to filter itself if the integrity of its outer surface is maintained. The actual process involved is the passage of liquid through a solid medium kept intact by a permeable textile. The process is not to prevent the passage of solids suspended in a liquid medium.
Geotextiles are rarely expected to withstand extremely aggressive chemical environments. Examples of places where they are used are the base layers of chemical waste containers or waste dumping areas. This can occur when runoff is generated allowing chemical waste to pass through the impermeable liner, or when the textiles are combined directly with the filtered discharge system on the impermeable liner. Another example is the use of textiles in contact with highly acidic dung soil in tropical countries where pH values can drop as low as 2. In industrialized countries where infrastructure development is established in highly polluted areas, geotextiles may be in contact with adverse environments.
Ultraviolet light tends to damage many polymers, but the addition of antioxidant chemicals and powdered carbon black additives significantly reduce this effect. The only time a geotextile will be exposed to the sun is during the construction period. Contracts must specify the minimum actual duration of sun exposure during construction. However, this situation varies according to the time of the year and latitude.
In summary, the duration of sun exposure in the UK and Northern Europe can be eight weeks in summer and twelve weeks in winter. However, in tropical countries, exposure to the sun without visible damage should be limited to seven days at any time of the year.
Mechanical Properties
The standard geosynthetic test specification in the UK is BS 6906, which includes:
1 Strength test by means of wide strip test
2 Pore size test by dry sieving
3 Test of normal incoming water flow on the textile surface
4 Puncture resistance test
5 Creep test
6 Perforation applicability test
7 Water flow test on the surface of the textile
8 Sand/geotextile friction behavior test
While not normally part of the mechanical requirements expected of a textile, the strength of the bonds between sheet edges is an important indicator of the geotextile's performance. As the textiles are spread over soft surfaces to support the weirs, parallel textile layers must be stitched together so that they do not separate under load. The strength of the sewn joints depends on the sewing thread. The sewn joint rarely exceeds the weft strength by 30%. Research and field practice have shown that the strength of sewn joints is dependent on the strength and tension of the sewing thread, the type of loop and the type of textile rather than the strength of the textile. Bond “effectiveness” is an erroneous but widely used concept, which is the ratio of seam strength to textile strength as a percentage. In fact, relatively weak textiles can be sewn in such a way that the bond is as strong as the textile and 100% efficiency is achieved.
As the textile becomes stronger, the relative strength of the sewn joint decreases, leading to breakage failures in solid fabrics. If the textile to be sewn is weak, eg 20 kN strength, it is reasonable to expect 75% sewing efficiency, but it is not possible to expect this efficiency from a 600 kN strength textile. However, solid textiles must be joined in order to support weirs or the like.
On the other hand, adhesive joints can be made by using one-component adhesives that start to set due to the humidity in the atmosphere. They are used to make bonds as strong as textiles, even for high-strength fabrics. Research is still needed on application methods, but their use will become more widespread in the future.
Beyond testing the strength of connections, tests that describe how textiles behave when compressed in or by a soil pile are urgently needed to be developed. Standard tests used in the past cannot do this. In this sense, research work has been initiated, but it does not provide a basis for theoretical analysis.
Filtration Properties
Filtration is one of the most important functions of textiles used in civil engineering works with soil. It is one of the widest applications of textiles and is used in lining ditches, under roads, in waste removal applications, in the construction of basement drains and in many other ways.
Of all the various uses of geotextiles, there is not only a beneficial filtration effect in a supported soil clump. In all other applications, including canals, outlets, river guards, sea guards, dam supports and concrete pouring, geotextiles perform a primary or secondary filtration function.
The permeability of geotextiles can vary greatly depending on the construction of the fabric. Various national and international standards have been set for the measurement of permeability at right angles to the surface of the textile (cross flow) and across the textile surface (intrasurface flow, conductivity). In civil engineering studies on the ground, it is important that water flows freely through the geotextile, preventing unnecessary water pressure build-up. The permeability coefficient is a number describing the permeability of the material under consideration, taking into account its dimensions in the flow direction, and its unit is meters/second. Effectively, the coefficient is a velocity that specifies the flow rate of water through the textile. Generally, it is on the order of 0,001 ms-1. A generally defined test measures the directly observed flow rate, expressed in liters of volume per square meter per second at 100 mm of pressure. Engineers also use a coefficient called permeation, which defines theoretical permeability independent of fabric thickness.
The filtration effect is achieved by placing the textile against the soil in close contact and ensuring the physical integration of the bare soil surface through which the water passes. Within the first few millimeters of the soil, an internal filter is formed and after a short pumping period stability is achieved and filtration takes place.
Chemical Resistance
Although the chemical mechanisms involved in fiber degradation are complex, there are four basic forms of degradation:
- Organic
- Inorganic
- light exposure
- Change of textile fibers over time
It also includes attacks with organic matter, micro and macrofauna. This is not considered to be the main source of degradation. Geotextiles can be damaged not primarily, but secondarily, from animals. For example, very few animals eat them, but in some cases, the textiles are buried underground, while some animals also puncture and damage them as they dig into the ground.
Microorganisms damage textiles by living on or inside the fibers and produce harmful by-products. Probably the environment where the highest strengths are expected for geotextiles is in areas where the sea hits the shore, where oxygenated water allows micro- and macro-organisms to grow and the moving water creates a compelling physical strain.
Inorganic attack is generally limited to environments where the pH is extremely high or low. Under most application conditions, geotextile polymers are not much affected. There are certain cases where polyester is damaged at pH levels greater than 11, but these are rare and well known.
Geotextiles become incapable of performing their filtration functions due to the organisms that clog the pores and multiply, or as a result of the chemical precipitation of saturated mineral waters that block the pores. Water from old mining operations, whether textile or granular, can quickly clog filters by being saturated with iron oxide.
Exposure to ultraviolet light for a long time damages the geotextile fibers.
However, laboratory tests have shown that fibers will degrade on their own over time, even if stored in dry, dark, cool conditions in a laboratory. Therefore, time itself is a damaging factor as a result of ambient temperature and thermal degradation, and it is not known to what extent the geotextile will degrade.
Geotextiles Made from Natural Fibers
Generally, geosynthetic materials have long lifetimes. For this reason, in simple applications, the user pays for something that exceeds his needs. Also, conventional geotextiles are often expensive for developing countries.
However, in many of these countries there is an abundance of cheap native fibers (such as jute, sisal, coir) and textile industries that can replicate common forms of geotextiles.
Although there are numerous animal and mineral-based natural fibers that can be used, important properties are not sufficient for the geotextiles in them, especially when the purpose of use is to support geotextiles.
Synthetic geotextiles are not only foreign to the soil, but also bring with them other problems. So much so that some synthetic products are petroleum-based.
Infinite absence of oil, the oil crisis of 1973,
The conflict between Kuwait and Iraq and the potentially volatile political situation of some other oil-producing countries have increased both the costs of products made from oil and the increased awareness of their consumption.
Natural fiber products of plant origin will be much more environmentally friendly than synthetic ones, and the fibers themselves are renewable resources and are biodegradable. Compared to natural fibers, the general properties of chemical fibers are in different categories. Natural fibers have high strength, modulus and moisture absorption, and elasticity with low elongation. Regenerated cellulose fibers have low strength and modulus, high elongation and moisture absorption, and poor elasticity. Synthetic fibers, on the other hand, have relatively low moisture absorption with high strength, modulus and elongation with reasonable elasticity.
Soil Support
While the soil is relatively firm when compressed, it is very weak in tension. For this reason, when a tensile-supporting material (geotextile) is added to the soil and is in direct contact with the soil, a composite material with excellent engineering properties is formed compared to the soil.
The load on the soil causes expansion. Therefore, under load at the interface between soil and support (assuming no shear, i.e. assuming sufficient shear strength at the soil/fabric interface), these two materials should elongate to the same degree, causing the same load on both support members, thus limiting the tension. must be redistributed in the soil. The support moves in a way that prevents lateral movement due to the lateral shearing force. Therefore, there is an additional lateral restrained stress that prevents displacement. This method of supporting the soil can be extended to slope and weir stabilization.
In most developing countries, geotextiles are used with great benefits in engineering applications such as slope stabilization, reinforcement of dams and flood banks, and construction on soft ground.
Such countries generally have renewable and abundant natural fiber sources. Since there is a surplus of labor in these developing countries, it is more desirable to undertake inexpensive short-term projects, periodically monitor and evaluate their stability, and if necessary, reconstruct them after a few years (i.e., if the natural material loses its strength due to the degradation process and cannot withstand the applied forces any longer). . Moreover, this procedure enriches the soil and improves growing conditions without causing harmful waste. While not recommended, these natural geotextiles can be a universal solution as they have a significant impact on the economies of developing countries.
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