Access roads on HDPE liners

GMA techline answers from Bob Koerner

Subject: Access roads on HDPE liners— I am designing a temporary waste storage facility that will be lined with a 1.5mm HDPE liner.

The facility requires access roads for the life of the facility—18 months. The access roads will be installed directly above the liner (1.5mm HDPE) and protective geotextile.

I’ve looked in “Designing with Geosynthetics” (R. Koerner), which recommends 600-900mm of crushed stone for the road base. Given the life span of the facility (18 months), do you think it would be possible to reduce the depth of stone using other geosynthetic materials? (Lora, Australia)

Reply: I recommended 600-900mm thickness based on heavy waste transfer trucks going into the landfill and the dynamic loads that they impose. If you can limit the weight (wheel loads) and control the truck drivers somewhat, you could probably use the 600mm value. I don’t see the thickness being less than this value. We have investigated two failures of liner systems being damaged under very thin cover soils over the liner system.

Regarding the use of crushed stone, my thoughts go to the type of leachate collection soil, and we are indeed using crushed stone for this application. If you are using coarse sand or fine gravel, go ahead and use it on the haul road as well, (i.e., match whatever soil you are using in the facility).

Lastly, do provide for drainage of water coming down the side slopes. We have also seen two washouts of haul roads in this situation. If you are using gravel, it will probably take care of itself. If you use finer soils, you might even need a pipe in the system.

Good luck.

Robert M. Koerner, Ph.D., P.E., NAE, robert.koerner@coe.drexel.edu.