Geotextiles: Functions & Fabric Constructions
Nonwoven and warp-knitted constructions are being used more and more for a range of geotextile applications.
Jürg Rupp, Executive Editor
Geotextiles have to fulfill a lot of demands. A major requirement is strength in both machine direction (MD) and cross direction (CD) in order to provide stability under the mechanical stress caused by debris and construction operations.
In 2008, the man-made Palm Jumeirah Islands were opened in Dubai. Today, there are big problems at the site, most probably because of inferior quality geotextiles.
Different Fabrics For Different End-uses
Geotextiles are one of the oldest forms of textile construction. Ancient Egyptians used reed mats for armoring banks and buildings. In the beginning, geotextiles were made of woven fabrics. Today, fabric constructions like nonwovens, or knitted fabrics such as warp knits or nets - so-called geogrids - also are used more.
According to Johann-Philipp Dilo, owner and chairman of the DiloGroup, Germany, North America and Europe currently are his business's largest geotextile markets: "The geotextiles segment is one of our key markets for the production of complete needlepunch production lines."
Durability And Efficiency
As mentioned above, geotextiles have to comply with a lot of requirements. Permanent functionality is essential for separation or filtration purposes. If the specifications are not achieved, the risk of failure of the whole system is possible. The main functions of geotextiles are separation, filtration, drainage, protection and reinforcement, and erosion control.
As a separating layer, geotextiles prevent the intermixing of adjacent soils or fill materials. Materials used are mainly nonwovens, woven fabrics and composite materials made of synthetic polymers. Selection of the right textile product depends on the grain size of the base course material and the anticipated loads during construction.
Dilo said most durable needlepunched nonwovens are made of polyester (PET) or polypropylene (PP). "On top of that," he said, "recycled fiber types, such as fibers made from PET bottle chips, are possible and quite common."
For degradable needlepunched nonwovens, it is possible to process virtually all natural fiber materials, which are chopped to a selected length.
This application is probably the most important one: Water pressure is one of the main reasons for damaged walls, dams or other man-made barriers. As a filter, the geotextile holds back soil components or other particles to allow the free flow of water. One has to distinguish between the mechanical strength for soil retention and the hydraulic filter effectiveness with the goal of low pressure drop for water drainage. Therefore, the geotextile's thickness plays an important, if not decisive, role and has a great influence on long-term, mechanical and hydraulic filter effectiveness.
Geotextiles is a key market for the Dilo Systems Hyperline, which comprises a complete needlepunch production line.
For drainage, geotextiles play more or less the same role as in filtration to discharge rain, groundwater or other liquids. Drainage systems are offered as individual components or as composite elements comprising at least one filter layer and a drainage layer. Runoff should be removed without pressure loss in the drainage layer. Geotextile drainage systems can replace traditional concrete or plastic tube constructions.
Protection And Reinforcement
Protection and reinforcement are very important geotextile functions for prevention of mechanical damage to inbuilt material, such as sealing stripes or coated material. Nonwovens and composites can be used as protective layers. For the protective function, important properties include drift punch and puncture resistance, as well as the element layer and geotextile surface thickness. Protective geotextiles are used in landfills and tunnels to protect impermeable material.
Installed under or between soil layers, reinforcing geotextiles pick up and absorb tensile forces to improve the soil layer mechanical properties. They are applied mainly as nonwovens or geogrids as supporting structures for the stabilization of dams on unstable ground. Reinforcements can save a lot of money because complicated constructive measures can be avoided.
Geotextiles for erosion control are often installed in the same environments as protection and reinforcement geotextiles. Erosion control geotextiles help to quickly stabilize embankments, whereas plants need a lot of time to grow their roots.
A lot of requirements must be met to achieve the specified properties. "Virtually all components from our portfolio from fiber preparation, carded web forming with crosslapper up to needlepunching are particularly well-suited for geotextiles to guarantee a reproducible and even quality," Dilo said. "Our customers want to have the whole production process in their hands to have total control over the quality of the finished product. Geotextiles made of needlepunched nonwovens provide value for money, have a good price/performance ratio, and combine strength with elasticity."
How important is the finishing of geotextiles? "In particular, the heat-setting process is very important for the quality," Dilo said. "This process contributes to an additional increase in strength, and is therefore coming to be more in demand."
Geogrids are gaining more ground in the markets thanks to the permanent evolution of the production process. They are used in construction for reinforcement applications including: separation of adjacent soil types; filtration to remove solid components; liquid absorption over a broad expanse; soil erosion prevention; mechanical protection; and soil stabilization in road and bridge construction, laying of railroad tracks, and dam and dyke construction; to name a few applications. Depending on end-use, geogrids feature various mesh sizes to distribute static and dynamic loads into the subsoil.
New Raschel Machine
Karl Mayer Malimo, Germany, recently introduced the RS MSUS-V rachel machine featuring parallel weft insertion and web feed-in facility, which can be used to manufacture a new geogrid type that is suitable for mining applications. These geogrids have a tensile strength of 1,000 kiloNewtons in both the weft and zero inlay directions, and comply with the DIN EN ISO 10319 standard. They feature a raw fabric weight of 3,300 grams per square meter, high-strength PET construction and flame-resistant coating.
The new geogrids are used to stabilize a mine's roof and sidewalls and provide protection from rock falls. They were developed using a RS MSUS-V machine with a gauge of E 3 and a 213-inch working width. Karl Mayer Malimo reports the machine can process glass rovings, basalt and all PET fiber counts; and can produce a wide range of constructions. Capabilities include the ability to incorporate layers of webs to produce composites in one step. Within the composites, direction-oriented yarns having a specified tear strength provide support and reinforcement, while the webs provide erosion protection, separation and filtration.
Geotextiles save a lot of concrete, transport costs and labor. However, if one wants to be successful in this promising market, the production site should be close to the region where the geotextiles will be used, mainly because of very high material transport costs.
"Geotextiles are tailor-made products," said Dilo. "It's first the product and then the price. Geotextiles have a bright future."
Click here to read this article in Chinese