Trails in Wet Areas (continued)

Sheet drains (Figure 35) are another form of composite made with a drainage core and one or two layers of geotextile. The core is usually made of a polyethylene sheet shaped like a thin egg crate. The core provides an impermeable barrier unless it has been perforated by the manufacturer. When used under the trail tread material, sheet drains provide separation, reinforcement, and drainage. Since they have greater bending strength than geotextiles or geonets, less tread fill is often needed.

Figure 35—Sheet drains have a large cross–section
that provides significant drainage capacity. If placed under
the trail tread, orient the sheet drain with the geotextile
side on the bottom and the plastic core on top. This
orientation reduces the amount of fill needed.

Sheet drains or geonets can be used as drainage cutoff walls (Figure 36). If the trail section is on a side slope where subsurface water saturates the uphill side of the trail, a cutoff wall can be constructed to intercept surface and subsurface moisture, helping to drain and stabilize the trail section.

Figure 36—Sheet drain or goenet used to intercept seepage.

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