They are extensively used during railway track construction for the separation of the track ballast from the sub-grade layer and to allow drainage to take place at the track’s edge.
In general, these products must provide strong damage resistance and be resistant to tearing or puncturing. They must have high water permeability to allow water to flow in both directions and also prevent sub-grade particles from migrating into the ballast to contaminate it.
Such products can either be simple layers of nonwovens or sandwich structures comprising nonwovens with HDPE laminates and/or plastic grids.
A recent innovation has also seen electrically-conductive materials laminated on to these products to make them detectable by ‘Ground Probing Radar’. This allows users to measure the exact depth of ballast above the geotextile.
Heavyweight nonwovens have been used for many years in combination with a sand layer to reduce contamination of the track ballast caused by ‘pumping’ or ‘wet-bedding’.
These terms refer to the way a slurry can be formed by water getting into the silt and clay of the sub-grade layer, which is then ‘pumped’ into the ballast layer as a result of the pressure and deflection in the ground caused by trains constantly passing over the lines above.
The consequences of ‘pumping failure’ – all too familiar to track engineers – can include subsidence, as a result of ground loss from the sub-grade layer, a loss of track alignment and contamination of ballast, leading to a reduction in its functional properties.
Any or all of these problems will significantly increase maintenance costs and ideally need to be prevented from the outset.
Such measures are increasingly significant, given the ambitious plans of many countries to build the necessary infrastructure for high-speed train lines.
World records
The world’s first high-speed train line was Japan’s Tokaido Shinkansen, which officially opened in October 1964.
The 0 Series Shinkansen, built by Kawasaki Heavy Industries, achieved maximum passenger service speeds of 210 km per hour on the route between Tokyo and Osaka. Shinkansen test runs reached a world record 581 km per hour in 2003.
In Europe, high-speed rail started during the International Transport Fair in Munich in June 1965, when DB Class 103 hauled a total of 347 demonstration trains at 200 km per between Munich and Augsburg. The first regular service at this speed was the TEE ‘Le Capitole’ between Paris and Toulouse.
In Europe, Austria, Belgium, Finland, France, Germany, Italy, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Turkey and the UK already have high-speed rail networks, with many other countries building or considering high-speed links.
But it is in Asia that progress will be most notable in the next few years, not least in China, where the construction of 13,000 km of high speed railway track is scheduled for completion by 2012 – greater than the length of all high speed lines currently in existence.
Perhaps even more impressive, however, given the country’s size and GDP, is the latest announcement by Vietnam that it plans to introduce a high-speed train line running the 1,630 kilometres between Hanoi and Ho Chi Minh City.
The funding of the proposed $56 billion line would mostly come from the Vietnamese government, with the help of Japanese aid. Technology used on the Japanese Shinkansen has been suggested for this new railway, allowing trains to run at speeds between 250 and 300 km per hour.
Current technology allows trains travelling on the single-track Hanoi to Ho Chi Minh City line to complete the journey in approximately thirty hours.
Once – and if – completed, Vietnam’s high-speed rail line would allow trains to complete the Hanoi to Ho Chi Minh City journey in just five hours.
Textile boom
Currently Vietnam has virtually no nonwovens industry of its own, meaning that all of the materials, such as the nonwoven geotextiles, would have to be imported.
The country, however, is currently enjoying a traditional textile manufacturing boom – its exports of textiles and garments, worth just US$116 million in 2001, have climbed 78 times to reach a value of US$9.1 billion in 2009.
Perhaps unsurprisingly, plans have been announced for the construction of new nonwoven manufacturing lines in Vietnam during 2010 – specifically to manufacture geotextiles.
The very latest geotextile developments will be showcased at INDEX 11 – the leading nonwovens exhibition which takes place at Palexpo in Geneva, Switzerland, from April 12-15 2011.
