Groz-Beckert KG

Newsletter 2 | 2011

Geotextiles –
a diverse market with attractive opportunities

What fashion do you see mountains, streets and tunnels wearing these days? The answer is geotextiles. In some ways they're like consumer textiles, because when it comes to aspects like separation, screening from view or insulation, these technical textiles fulfil similar requirements to apparel textiles. But there are big differences too - and in the following article we'll be providing a comprehensive account of them.

Most people associate the word "textile" with textiles used in apparel. The prefix "geo-" brings to mind such things as geography or geometry. Geotextiles combine these two worlds.

Geoplastics: a definition

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Materials today
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Materials back then: straw
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Reeds

Thousands of years ago various different natural materials were being used to reinforce soil - straw, for instance, or reeds. The basic concept has remained unchanged till the present day - but modern methods and materials can hardly be compared to the technology used in the old days. Wood, stone, concrete or perhaps cotton were the preferred materials in highway construction during the 20th century; today we usually use synthetic polymers, also known as plastics for short.

In this regard, we talk of so-called geoplastics. These took very little time to fully establish themselves because of their diversity and flexibility. They also bring benefits in cost terms: thanks to geoplastics, we can make major savings on construction materials such as sand, gravel or clay. Geoplastics (GSY) are initially differentiated in their properties as permeable or impermeable media according to DIN EN ISO 10318. Among geo-membranes (GMB), geosynthetic clay liners (GCL) are considered to be virtually impermeable. The permeable materials are geotextiles (GTX) and geotextile-related products (GTP).

Technical sub-groups


Geotextiles (GTX)



Geotextile-related products(GTP)



Sealing membranes (DMB)


Fabrics GTX-W

Geogrids GG

Polymer TE-GMB

Nonwovens GTX-N

Geonets GNE

Bituminous B-GMB

Geotextiles GTX-K 

Geocells GCE 

Geosynthetic clay liners GCL 

 

Geostrips GST

 

 

Geomats GMA

 

 

Geospacers GSP

 

Geotextiles with bio-properties

Biodegradable geotextiles

Nonwovens made of natural fibres can also be classified as geotextiles, because weatherproofness is not always required. Natural geotextiles are used in particular for erosion protection. The objective here is to protect a slope or embankment from natural soil removal until natural greening has taken place, after which the geotextile is no longer needed. Geotextiles made from natural fibres are biodegradable - which makes them especially suitable for these purposes.

Subdivision of geotextiles

With regard to classification and terminology, the rules of certification bodies and norm committees are not always taken into account. Geosynthetic clay liners or geonets, for instance, are generally regarded as geotextiles as well. In this regard there are several ways of classifying geotextiles. Subdividing them can be done according to their type of structure, their sphere of application or their particular function.

Classification according to structure

Fundamentally, three different types are distinguished:

  • Fabrics are geotextiles consisting of yarns or threads which normally cross each other regularly at right angles. They are always used wherever high tensile strengths are needed. In the case of static load they are also suitable as filters.
  • Nonwovens are formed when fibres laid on top of each other on a surface are reinforced. Different stretch characteristics can be achieved by means of different reinforcement methods: needling, gluing or melting. Nonwovens are mainly used for separating or filtering.
  • Composite materials are fabrics, nonwovens or other materials that are surface-connected. The properties of different geotextiles can therefore be combined.

Classification according to purpose

Geotextiles are predestined for numerous applications:

  • Traffic route construction (soil consolidation, bearing layer reinforcement, roadside drainage, embankment creation, soil stabilization, rainwater retention basins)
  • Roof constructions (roof rear ventilation, roof landscaping)
  • Waste disposal sites (surface sealing)
  • Slope reinforcement (surface securing)
  • Hydraulic engineering (erosion protection)
  • Building drainage (cellar drainage, drainage of vertical walls, drainage and lost formwork, horizontal pressure-resistant drainage, supporting walls)
  • Tunnel construction (open cut method)

Classification according to function

When geotextiles are classified according to function, the following properties are usually mentioned:

  • Separation: The mixing together of different types of soil and filler material such as sand, gravel or earth is prevented. This method is often used in highway and railway construction.
  • Filtration: Here geotextiles serve firstly as a barrier, blocking particles of various soil types, and secondly they guarantee that water can flow through. Applications apart from railway and highway construction also include embankment reinforcement.
  • Drainage: Here, water is removed via artificial structures, without pressure and in a targeted manner.
  • Protection: In the construction of waste disposal sites and tunnels, the protective effect is especially relevant.
  • Reinforcement: Embankment and slope subsidence during landfills due to weak subsoil is avoided. Embankments that are steeper than the natural slope angle can be secured.
  • Stress compensation: Geotextiles are primarily used for stress compensation in highway construction. This reduces differential movements of individual layers and thus prevents cracks and fissures that could adversely affect the road surface in the long term.

Geotextiles in highway construction

Diagram: Geotextiles in highway construction

 Layer description

 

1

Road surface

2

Filler material

3

Geotextile layer

4

Soil

Robustness categories of geotextiles

Geotextiles have to satisfy several different requirements at the same time. These include separation, filtering and drainage, whereby mechanical stress generally reaches the limits of resilience. What a geotextile can and cannot do is ultimately decided by the so-called geotextile 'robustness categories'. The first job is to establish which category a geotextile comes under.

During the testing, the following methods are used:

  • Measurement of the puncture resistance by means of experiments according to DIN EN ISO 12236
  • Tensile strength testing with the aid of the elongation test in accordance with DIN EN ISO 10319. This applies primarily to products made from film strips, spliced yarn or multifilament yarns.
Determination of the dimensions per surface unit in accordance with DIN EN ISO 9864. The measurement values enable the geotextile to be classified into various different robustness categories. Depending on the type of geotextile, there are five different robustness categories:
GRK 1-5

Production of geotextiles

In the production of geotextiles, all textile production methods are in effect possible. The key factors here include economic efficiency, productivity and physical properties. As a result, nonwovens are primarily used because of their diverse potential. As composites they can consist of several layers, they can have an integrated multifilament layer for reinforcement, be filled with minerals, or simply be an ordinary needlefelt without backing. Reinforcement is done either chemically, thermally or mechanically, or via a combination of these three methods.

The high demands placed on the physical properties of the textile surface automatically require state-of-the-art production methods. Use of the right machines and tools plays a crucial role here. For this reason Groz-Beckert offers you special felting needles that are incomparable in terms of their long service life and high productivity.

We recommend that you also read the article "The Technology of Geotextiles" in this Online Newsletter.

More information on everything to do with felting and structuring needles and jetstrips is available at the Groz-Beckert Website.