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We are carrying out a landfill capping job for a solid waste site. The slope is 1:1.75 and [is currently] lined with an HDPE liner. The height of the bund is approximately 12.0m.

As per clients’ direction, we are supposed to lay a 200-gsm geotextile, followed by one-sided geocomposite drainage net 5mm-thick, followed by 45cm of soil and landscaping.
I have mentioned to the client that soil will not be stable on a 1:1.75 slope and that it be on geocomposite net that is resting on smooth HDPE liner.

Can you please suggest other alternatives to place the soil and how to get suitable compaction on this?

(Ran | Washington)

Hi Ran,
Our database for interface shear of a nonwoven geotextile on smooth HDPE is
11 degrees peak and 9 degrees residual. The unbonded interface strength between the geotextile and geonet isn’t much better.
Thus, the only way the geotextile and the
one-sided geonet composite will stay on
the slope is by means of its fixity in the
anchor trench. Even if this anchor trench is substantial, the geotextile and geonet composite will likely be overstressed by
the bulldozer and cover soil and will likely
fail in wide-width tension.

My suggestion is to change the design to double-sided textured geomembranes and double geotextiles thermally bonded to both sides of the geonet core. Now, with a substantial anchor trench and low-ground contact bulldozer, you might get the soil up the slope. In this regard, a tapered cover soil would help if room at the toe of the slope
is available. Ran, a 30-degree slope angle is really steep to even walk on, let alone to construct (yuck!).

Bob Koerner | GMA Techline