Geotextile in Permeable Pavement
By Robert Bowers, P. Eng., ICPI Director of Engineering
ICPI Director of Engineering, Robert Bowers, P. Eng., receives questions from members in need of advice and tips regarding permeable paver driveways.
One recent question referred to a residential permeable pavement driveway, and when to use geotextile versus when to not.
Sometimes called filter fabric, geotextile is made of synthetic fibers formed into a sheet that are designed to allow water and gases to pass through them, while retain soil particles. Geotextile separates and contains the base from the underlying soil subgrade. It allows the base to shed water, and prevents the soil around it from working its way into the base.
Without geotextile, the soil will work its way into the base and weaken it. This is a slow process that happens when the soil is saturated with water or during periods of thawing. Geotextile stops this process and extends the life of the base by many years. Geotextile is recommended for use over silt and clay soils. It is not essential in sandy soils.
The decision to use a geotextile in permeable pavement should be based on the same criteria used when considering use of a geotextile for the traditional interlocking concrete pavement: 1) confinement of the base aggregate and 2) separation of the base aggregate from the subgrade soil. Confinement and separation created by the geotextile will help ensure that the base in a pavement system will function longer than a base that is not wrapped in a geotextile.
However, the selection criteria also requires that the geotextile have a high level of permeability. Typically, geotextile manufactures report the materials ability to pass water through it as the permittivity. The greater number, the faster water will pass through.
The member went on to ask if they should use the same woven geotextile as specified for traditional paver systems?
If the soil is structurally sound, like a sand-gravel mixture, the use of non-woven needle punched geotextile should work. It was suggested that a thicker non-woven needle punched geotextile, such as an 8 oz., be used because of the damage it would experience from compacting larger angular aggregate on top of it.
If the soil is weaker, like silt or clay, the use of a woven geotextile would be appropriate. However, it was recommended to look for a geotextile with a higher permeability to allow the water collected in the system to pass through the geotextile and infiltrate in the subgrade unimpeded. Typical slit-tape woven geotextile would not be suitable because of its low permittivity. It is recommended to use a mono-filament, multi-filament or fibrillated-filament type woven geotextile.
Have an engineering or technical question? Robert is always ready to respond with the latest technical resources and information.
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