Liner questions

From the GMA Techline

RE: Liner questions
I am designing a surface impoundment with interior side slopes of 1.5H:1V. This impoundment requires (per regulations) a geosynthetic clay liner (Bentomat DN or equivalent), 40-mil HDPE secondary liner, and 60-mil HDPE primary liner. A leak-detection system has been requested.

The pit is small (approximately 500ft x 200ft) without much travel distance for fluids should a leak occur. To avoid too many liners on a steep slope, I would like to use two textured HDPE liners as both the primary and the secondary without adding a fourth layer in for the leak-detection system.

I have the following questions:

• Is there information available about the transmissivity of two textured HDPE liners? Does it matter if it is blown or structured texture?
• What is a typical range for an interface friction angle between two textured HDPE liners?
• Any information or references would be appreciated.

(Melissa | Missouri)

Reply: Tough questions … 34 degrees is at, or slightly higher than, the best of geosynthetic interfaces (e.g., nonwoven to textured, internal to GCLs, etc.). So you are flirting with disaster to begin with.

It is much worse with a GM-to-GM even when they are textured. In fact, even more so, since the shear plane must ride up on the asperities. What remaining transmissivity there is depends on the normal pressure applied.

Clearly ASTM D4716 is the appropriate test to use and will also allow one to get a glimpse of how the asperities behave.

Lastly, it very much depends on how the texturing has been manufactured. I suspect that blown film will indeed be different from structured with regard to shear strength and transmissivity.

Melissa, you need to do some lab testing to quantify my commentary.

Bob Koerner | GMA Techline