Essential assistance for infrastructure
Nonwoven geotextiles have been employed to reinforce and support many well-known landmarks – from the slopes of exclusive ski resorts in the Swiss Alps to the world’s largest artificial island, its highest airport and its biggest-ever land reclamation project.
Not to mention the Panama Canal and the Empire State Building…
Around 750,000 square metres of nonwoven geotextiles are sold each year according to EDANA – the equivalent of 185,000 football fields – with 60% employed in the construction of roads.
These nonwovens – primarily densely-needled or spunbonded materials based on polypropylene or polyester – are part of a family of geosynthetics that today includes woven fabrics, geocells, geofoams, geogrids, geonets, geomembranes and a number of other specialised materials.
To meet the needs of global construction projects, the leading manufacturers are increasingly providing these materials in multi-layer combinations to solve specific functional requirements.
In addition to roads, geosynthetics are used extensively in the construction of railways, retaining structures, embankments, tunnels, pipelines and landfills. In addition, they are employed in coastline protection works and marine structures, while wastewater treatment in mining and the upstream oil and gas sectors is a key area of growth.
The functions they can provide include materials separation, filtration, drainage, soil reinforcement, erosion control, sealing, stress relief, adhesive bonding, confinement and monitoring.
In addition to the speeding-up of construction processes and cost advantages, when compared to simply using natural soils, geosynthetics also have a much lower environmental impact. This reduces both CO2 emissions and the need for excavations in quarries or in other environments.
A key element in many construction projects, meanwhile, is accommodating challenging terrain that requires walls and steep slopes. Here, geogrids and geotextiles often work in concert with soils to construct safe, resilient and long-lasting surfaces. They are also used to achieve varied geometries and the desired aesthetic appearance. In addition, they can be used with locally formed soils which cuts down the need for shipments of construction materials to a site considerably.
In Switzerland, the area of Alps covered by geotextiles has doubled in the last seven years. According to a recent study published in Cold Regions Science and Technology, the technique can slow ice melting by 50%, which allows longer tourist seasons. The installation of geotextiles is also fairly simple, requiring less infrastructure, energy and water compared to other methods to reduce melting, such as artificial snow production.
This is, however, no solution to the larger and longer-term problem of the gradual erosion of glaciers due to global warming – covering Switzerland’s 1,000 largest glaciers each year would cost about $1.5 billion, according to Matthias Huss, a glaciologist at the University of Zurich and co-author of the study.
In hotter climes, Palm Island Jumeirah is an archipelago of artificial islands in Dubai, created using land reclamation which extends into the Persian Gulf. It is part of a larger series of developments called the Palm Islands, which when completed, will together increase Dubai's shoreline by a total of 520 kilometres.
Nonwoven geotextiles 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.
For the breakwater, the selection of the geosynthetic 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 extensible enough to conform to irregular seabeds and be sufficiently porous to retain fines, while allowing the free flow of water.
At a height of over 1,370 metres, India’s new Pakyong Airport opened following a nine-year construction project.
Pakyong is in Sikkim, a fairly isolated and landlocked Indian state located in the Himalayas and well-known for its lush green topography. In addition to its remote location, it is subject to a four-month Monsoon period, with heavily weathered ground conditions and a susceptibility to earthquakes,
Once the site had been selected, the mountainside slope had to be excavated up to around 110 metres and the valley side slope required retention structures up to 74 metres high in order to first make the ground level for the airport to be constructed.
The materials for the retention structures consisted of pre-assembled units of double-twisted wire mesh and polymer-coated steel wire, employing geogrids for primary reinforcement and layers of nonwoven geotextiles to provide drainage, secondary reinforcement layers and pipe protection.
Chel Lap Kock Island
Hong Kong International Airport, meanwhile, involved expanding Chel Lap Kock Island from an area of three-square metres to twelve and 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.
Some 900,000 square metres of nonwoven geotextiles were also employed in the expansion of the Panama Canal which created a new lane of traffic through the construction of a new set of locks, doubling the waterway’s capacity. The Panama Canal is approximately 80 kilometres long between the Atlantic and Pacific Oceans and the new locks created the increased canal width and depth necessary to support modern container ships.
A total of 18 water saving basins were waterproofed with PVC geomembranes and geocomposites, with advanced geotextiles acting as anti-puncture layers and increasing the tensile strength of the waterproofing liners.
For this project, approximately 800,000 square metres of lightweight nonwoven geotextiles were supplied for the PVC waterproofing membrane and more than 100,000 square metres for the protection function.
A rapidly-growing application for geotextiles is meanwhile in green roofing and this has even extended to the iconic Empire State Building.
The installation of grass and other plants on a building’s roof has a number of benefits, not least in absorbing rainwater and releasing it slowly back into the atmosphere through evaporation, or if there’s too much build-up, allowing the water to trickle slowly into drainage systems to ensure they aren’t overwhelmed.
There are other benefits too, including insulation and cooling properties for the building, as well as the promotion of biodiversity in built-up areas.
In the $550 million Empire State Building project, various systems were employed on the 21st, 25th and 30th floors, combining a variety of nonwovens as well as polymeric entanglements fused to further nonwovens for the growing medium, the distribution and storage of water within the root zones, excess water drainage below vegetated layers and the prevention of root encroachment into the structure of the building.
Impressively, this has reduced the annual energy consumption of the entire building.