Perforated pipe (sometimes called weeping tile) requires a wrap of geotextile in order to prevent soil fines from getting into the pipe and causing the pipe to clog. Filter sock supplied by the pipe supplier can be limited in size or performance. Layfield offers custom filter sock sewing for all your filter sock needs.
The Importance of Proper Filtration Design
In any drainage application it is important to design the filtration properties of the geotextile to the soil expected at the site. A site specific design will require a geotextile with a controlled opening size (called Apparent Opening Size or AOS). There are two problems that can occur with an incorrectly selected geotextile. If the textile is too open then the soil fines will flow through into the pipe and can cause siltation of the pipe. In the case where the opening size of the geotextile is too small the geotextile can clog and prevent water flow. Both of these problems can lead to drainage failure and the inevitable expensive repairs. Layfield recommends that you select a geotextile based on proper drainage design.
Layfield has geotextiles with a wide range of AOS’s available. In many cases the filter sock supplied by the pipe company is a knitted sock with a very large opening size. Most often we are called upon to provide a filter sock with a much smaller opening size as the soil types are fine grained. Typar geotextiles have the widest range of opening sizes of any geotextile on the market; between 600 and 74 microns (30 to 200 US Sieve). Needle-punched non-woven geotextiles by comparison have a narrow AOS range of between 300 and 150 microns (50 to 100 US Sieve). Layfield stocks filter sock made with Typar 3201 geotextile in a variety of widths.