Pipeless drainage system
Geosynthetics | April 2008
GMA techline answers from Bob Koerner
Subject: Pipeless drainage system — We are designing residue cells for a mine in northern Minnesota, and they’ve opted for a pipeless drainage system in the cells. The residue is a very fine, saturated, silt-sized particle, quite sticky, low LL/PL.
I’ve done a little work with geotextiles, but my gut tells me that I’d need more of a filter than just a geotextile to prevent clogging. Can you recommend any products, companies, or references on geocomposites and pipeless drainage systems? (Seth, Minnesota)
Reply: I presume that you are considering a sand/gravel drainage system, and you are correct that a perforated pipe is traditionally used for efficient removal of the liquid (leachate?). With a geotextile filter over the system–having a pipe or not–there is a chance for excessive clogging, particularly with the upstream soil you describe.
To evaluate geotextile candidates against the site-specific soil, there are 3 tests available: gradient ratio, hydraulic conductivity ratio, and fine fraction ratio. Commercial labs run these tests on a routine basis.
Regarding the drainage system, per se, you might consider a biplanar or triplanar geonet composite. While the same issue of potential geotextile clogging is present, you do not need a perforated drainage pipe since the flow regime in a geonet composite is much faster than with soils.
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Comments are the opinion of individual posters and do not reflect the views of Geosynthetics or Industrial Fabrics Association International.
2:29 pm CST
Drainage
Wich is the most used desing method for drainage systems in MSEW with geosynthetics or what can i do for desing a system for drainage in the MSEW
2:36 pm CST
Re: Drainage
Editor’s note: We received the following information from Bob Koerner.
My original response still is reasonable and so I stand with what was written. That said, the question as to what type of drainage system is most common I think that a sand or gravel layer with an embedded perforated pipe system is the most common on a historical basis. I say this because that is how the EPA Guidelines were originally crafted. The change over the recent ten years is to use a geonet composite directly on the geomembrane with the sand or gravel over it, i.e., no pipe system at all.
For both of these strategies, the design will control in many cases. This design uses the HELP computer code which was developed for the U.S. EPA and is now used worldwide for design of leachate collection and removal systems. Hope this helps……Bob Koerner
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