Many articles about installing agricultural drains recommend that you place a geotextile in the trench before the initial gravel surround and then wrap the geotextile over the gravel afterwards.
You can also buy agi pipe with a geotextile “sock’ around it like this:
The idea is that the geotextile prevents the gravel,or the pipe getting clogged with fine materials.
Its something I used to do, but . . . I DO NOT recommend this anymore.
The Reason
Practical experience has shown that what happens is:
- If you wrap the gravel with geotextile the geotextile actually collects all the particles on its surface and gets clogged up. This stops the water getting to the gravel and on through to the pipe.
or
- If you wrap the pipe and put the sock around the pipe its only the very fine particles that get through the gravel but they then get caught in the ‘sock” in front of the slots. This again stops water getting into the pipe and draining away.
Recomendation
It far better to just go for a 10mm or smaller gravel surround.
This stops the larger particles.
Any fine material that gets through the gravel will be that fine it will easily pass through the slot and likely to get washed down the pipe.
See Agricultural drains for more information.