Geotextile breakthrough - nonwovens make the impossible possible
The world’s largest artificial island, the biggest-ever land reclamation project and the most prized ski slopes in the Swiss Alps all rely on layers of nonwoven fabrics for their stability.
And in 2016, some 900,000 square metres of nonwoven geotextiles are being employed in the expansion of the Panama Canal.
In infrastructure projects around the world, permeable geotextiles – typically made from polypropylene or polyester – have a range of functions to perform in respect of separation, filtration, reinforcement, protection or drainage.
Construction teams have employed them for decades where stone is used as the base for roads and railway lines. When stone is placed against indigenous soil there is always a danger of it becoming contaminated or unstable as a result of both the relentless weight placed upon it over years of traffic and of water movement through the soil.
A geotextile layer beneath the base of the stone allows the water to drain away but at the same time prevents instability and contamination.
Geosynthetics are also used extensively beneath coastal defences, where a robust layer laid below rock armour or pre-cast concrete units ensures that the underlying soils are not leached out by tidal action, undermining the whole structure.
Palm Island Jumeirah is the first of three islands that were initially planned to extend Dubai’s coastline from 72 kilometres to a staggering 1,500 kilometres, being designed in elaborate patterns with extending ‘fronds’.
Work on the other islands, however, has now been shelved for the immediate future.
But Palm Island Jumeirah was completed in 2007 at an estimated cost of $12.3 billion and having involved around 40,000 workers. It was created by pouring sand fill onto the deep seabed using dredgers and then by employing a technique known as ‘rainbowing’, in which the sand fill was sprayed over the surface of the rising island.
Palm Island Jumeirah now measures five square kilometres and has 17 fronds, each two kilometres long and 75 metres wide, which are protected by a 12 kilometre-long breakwater.
It is the home to many different residential complexes and luxury hotels and also boasts the first monorail in the Middle East which connects the island to the mainland.
Nonwoven geotextiles supplied by Fibertex of Denmark were widely employed in the construction of Palm Island Jumeirah, which in total employed some 90 million cubic metres of sand and rock.
The engineered fabrics were used in the breakwater to separate the rock base from the sand ‘beach’ and also under the roads on each of the fronds. In addition, they were used for landscaping and in the drainage and storm water sewers.
As far as the breakwater was concerned, the selection of the geosynthetic material had to take into account the water depth, the wave height, the type of rocks that were to be dropped onto the fabric and the height from which they would be dropped. The material also had to resist puncture, be flexible enough to conform to irregular seabeds and be sufficiently porous to retain fine particles, while allowing the free flow of water. In areas where wave heights of three metres were normal, one of the rocks dropped from a height of four metres required a geotextile with a puncture resistance of 12,000 newtons.
Chel Lap Kock Island
Hong Kong International Airport, meanwhile, involved expanding Chel Lap Kock Island from an area of three square miles to twelve and required the reclamation of some 367 million cubic metres of stone, sand and gravel.
In total, more than seven million square metres of nonwoven geotextiles were used in this project, both to stabilise the sub-base and prevent migration and mingling of materials, while allowing the free movement of water. They were also laid as a filtration layer along a wide stretch of the coastline.
The current Panama Canal expansion now underway – the largest since its original construction – will create a new lane of traffic along through the construction of a new set of locks, doubling the waterway’s capacity. The Panama Canal is approximately 80 kilometers long between the Atlantic and Pacific Oceans. The new locks will create the increased canal width and depth necessary to support modern container ships. At total of 18 water-saving basins, nine on the Atlantic side locks and nine on the Pacific side locks, were waterproofed with PVC geomembranes and geocomposites.
To successfully waterproof and provide long-term protection support to the canal water saving basins, Italian nonwovens producer Manifattura Fontana supplied advanced geotextiles to act as an anti-puncture layer and to increase the tensile strength of the waterproofing liner. These nonwovens are based on high tenacity, UV resistant fibres supplied by Fontana’s partner and INDEX™17 exhibitor Beaulieu Fibres International. Fontana also supplied
PVC geomembranes to which the nonwovens were heat bonded and the resulting geocomposites are capable of meeting the extensive physical requirements and high mechanical demands.
For this project, Manifattura Fontana supplied approximately 800,000 sq. metres of lightweight geotextile for the PVC waterproofing membrane and more than 100,000 sq metres of heavy-duty geotextiles for the protection function where the waterproofing liner was covered by ballast.
“For such a significant, large-scale project our customers need to rely on the best mechanical performance and hydraulic characteristics, as well as the durability of materials,” said Francesco Fontana, owner of Manifattura Fontana. “Consistency of these high standards is essential in order to guarantee the final result. On the basis of 15 years of technical collaboration with Beaulieu Fibres International and its fibre expertise, we knew the company would be the right sole supplier to help us achieve geotextiles reaching the high standards required, within the tight timescale. We were proved right.”
Geotextiles are also now increasingly being employed to prevent the melting away of Swiss glaciers, which Zurich University has predicted will largely have disappeared by the end of 2050 unless drastic protective measures are taken.
At the Gemsstock summit station in Andermatt, Switzerland, around 3,000 square metres of nonwovens have been laid out to prevent the further melting of the glacier, which has receded by approximately 20 metres just 15 years.
The nonwoven protects the layer of snow from heat and UV radiation, filtering out other natural influences of the environment and as a consequence, largely prevents the snow and ice from melting. The two-layer composite nonwoven is needlepunched, ecologically compatible and free from harmful substances. It had already been widely used as a geotextile in millions of square metres of sub-grade tunnel and hydraulic construction projects in Europe.
Nonwoven geotextiles have also been employed at Saas Fee resort, the famous car-free glacier village which lies on a high plateau 1,800 metres above sea level, at the foot of the highest Swiss mountains – the Mischabel chain.
Some of the biggest names in the nonwovens industry are heavily involved in the supply of geosynthetics and will be exhibiting at INDEX™17 in Geneva next April.
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