From the GMA Techline
Subject: Geotextile fabric We are specifying geotextile fabric:
- between the soil media (in a raingarden) and the underlying stone that contains the underdrain pipe.
- between the sod and the underlying stone (water quality swale) that contains the underdrain pipe.
- the top, bottom, and sides of an infiltration trench (filled with VaDOT #57 stone).
We are getting conflicting views as to what we should specify. Please advise.
Reply: The answer to your situation is quite straightforward. The association of state highway officials (called AASHTO) has a neat specification for your applications under the designation of AASHTO M288. It is available from all state highway departments—just contact your local geotechnical engineer.
I should add that the part of the specification that you want is “Drainage Specification.” It will work for all three of your applications. I might also add that all manufacturers know of this specification and make products oriented toward the stated criteria.