Protective role ... geotextiles used in a water reservoir.
Nonwovens offer versatility, strength
From roads and railway construction to erosion control, geotextiles are playing an increasing role in the integrity and safety of structures. Austria-based geotextiles specialist Geofelt elaborates on the critical role played by nonwovens.
01 May 2009
IN the building of transportation structures, in hydraulic engineering, in the construction of increasingly more sophisticated landfill waste disposal facilities, and other applications, nonwoven geotextiles are playing a variety of roles in ensuring the integrity of structures.
Nonwoven geotextiles are planar, permeable, polymeric textile materials used in contact with soil and/or other materials, in geotechnical or engineering applications.
They are made up of randomly-oriented fibres or filaments (polypropylene, polyester fibres), bonded together by mechanical or thermal processes.
Nonwoven geotextiles present characteristics such as mechanical resistance, permeability to water and gases, filtration (retention of soil particles), drainage capacity, protection efficiency and durability. Moreover, being supplied as rolls, they are easy to be installed.
Nonwovens are the most widely-used geotextile type in the geotechnical and environmental engineering applications, thanks to the different multiple functions they can perform like separation, filtration, drainage in the earth works and separation, protection and drainage in contact with waterproofing systems.
Roads & railways
In road construction, nonwoven geotextiles are used as a separation layer between base soil and fill material, and as a filtration layer whenever finer soil particles may be eroded by the forces of pore water. The presence of a geotextile has a reinforcement effect to the road foundation, where bearing capacity is remarkably improved.
The use of this geosynthetic layer is essential to ensure the full efficiency of the road during all its service life, avoiding expensive maintenance operations.
Nonwoven geotextiles have different applications in railway works.
In the construction of ballasted railway lines, these products are placed between the ballast and the subsoil, or between the in-situ soil and a compacted fill material layer, in order to keep the two materials separated. Nonwovens perform the separation and filtration function as well as the drainage function, conveying the pore water to the water collection system at the sides of railway track.
Without the use of geotextiles, the dynamic loads generated by train traffic would result in the infiltration of the ballast by fine soil particles, especially in the case of soft saturated soils. Thus, the original mechanical characteristics of the ballast would change within a relative short time, causing a progressive deformation of the track structure. Expensive maintenance operations would therefore be necessary. Using the nonwoven geotextiles, the service life of the railway line is considerably extended, with the advantage of higher railway track safety and cost saving.
Nonwoven geotextiles can be also used in the renewal of existing railway lines, where the polluted ballast is replaced by new clean aggregates; the products are laid as separation and filtration layers between the new ballast and the subsoil.
In the new ballastless track lines, nonwovens are also used as the separation and protection interlayer between the track slabs and the concrete foundation below.
Tunnels
In the waterproofing of tunnels, the geomembrane must be adequately protected against the risk of puncture and abrasion, in order to preserve its original characteristics of impermeability.
The nonwoven geotextiles are installed between the geomembrane and the irregular, rough surfaces of tunnels. They can also perform a drainage function of seepage water.
High-tenacity polypropylene nonwoven geotextiles are used in railway, road and waterway tunnels, thanks to their characteristics of puncture resistance, protection efficiency, drainage capacity and chemical resistance.
Erosion control
Permeable revetments are often used in coastal and river bank erosion control structures against the action of waves and currents. These are rocks, or artificial elements such as concrete blocks or gabions. Under this covering layer, the fine particles of natural soil are subjected to drag forces generated by hydraulic gradients.
A filtration system between the revetment and the base soil is, therefore, to be designed. The hydraulic characteristics of this system must ensure an adequate retaining capacity of fine soil particles, allowing in the meantime the water to pass through, without generating dangerous pressures on the revetment.
Nonwoven geotextiles are used for this purpose as a filtration layer, offering adequate retaining capacity and permeability normal to their plane. The site conditions may be more or less critical for the geotextile, according to the type of revetment, depending on the characteristics of the base soil and according to the drop height of covering elements.
High-quality nonwoven geotextiles offer high mechanical resistance and energy absorption capacity, which make them suitable for use even in critical conditions of installation.
Waste disposal
Nonwoven geotextiles are largely used in waste disposal works and in the reclamation of polluted land areas. An effective containment of leachate and polluted liquids by means of geomembrane liners entails that these waterproofing systems must be adequately protected against the risk of mechanical damage. In fact, the geomembranes in contact with rough surfaces or draining gravel are usually subjected to high contact pressure, and can be easily punctured without the protection afforded by a high-efficiency nonwoven geotextile.
The nonwovens are also used in the capping operations of landfills, where the covering fill material must be separated from the gravel layer for the drainage of rain water. In this way, the nonwoven geotextile is installed between the covering material and the gravel layer, performing both functions of separation and filtration.
Reservoirs & dams
In the waterproofing of reservoirs, the geomembrane must be adequately protected against the risk of puncturing and abrasion, in order to preserve its original characteristics of impermeability.
Thanks to their high protection efficiency, nonwoven geotextiles are installed between the geomembrane and the irregular, rough laying surface, either soil or concrete.
In the construction of earth dams, the nonwovens perform the filtering function, preventing the soil being eroded by hydraulic forces.
In the rehabilitation of concrete dam, nonwoven geotextiles are placed between the surface of upstream dam face and the geomembrane used for its waterproofing. In this case, they perform a double function: protection of the geomembrane in contact with a rough surface and the drainage of seepage water present in the dam face.
