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home > pervious surfaces > pervious surfaces types > construction options > geotextiles
In order to reduce the effects of water on the strength and stiffness properties of the subgrade below pervious pavements a geotextile separator layer should always be provided over moisture sensitive or fine grained subgrades. This will enhance the performance of the pavement structure in two ways:
Geogrids or geocellular confinement systems may also be incorporated into
the granular layers in order to increase the stiffness and therefore reduce
the required thickness of the layers. They can also be used as separation
layers to prevent migration of fine particles between unbound layers and play
an important role in removing pollutants.
Designers need to take careful consideration of geotextile properties with
respect to the selection and specification of geotextiles. Many designers
refer to layers within the construction that require specific properties merely
as "geotextiles". The variability in performance with commercially available
geotextiles is vast. They can vary in thickness from a few microns to tens
of mm, can be manufactured from a diverse range of raw material (for example
polyethylene, polypropylene, polyesters) and be any blend of the foregoing
with various mixtures of virgin or recycled material. Geotextiles can be woven,
non woven, needle punched or thermally bonded all with different pore sizes
and permeability.
All these aspects give rise to a huge variance with regard to physical properties
and performance of geotextiles, together with UV resistance, durability and
robustness during installation. All too often designers specify a geotextile
based on a popular brand name alone without due consideration of the required
material properties.
Guidance will provide recommendations on the specification of geotextiles to ensure
that they provide adequate filtration to prevent migration of fine soil particles,
together with appropriate permeability so they do not limit flow of water
in the system.
The geotextile must also be able to resist the punching stresses caused by
loading on sharp points of contact and have sufficient strength to resist
the imposed forces from traffic or other loading.