Pipeless drainage system

From the GMA Techline

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.

Bob Koerner | GMA Techline