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Trail Construction and Maintenance Notebook

Trails in Wet Areas (continued)

Puncheon

Puncheon is a wooden walkway used to cross bogs or deep muskeg, to bridge boulder fields, or to cross small streams. It can be used where uneven terrain or lack of tread material makes turnpike construction impractical (Figure 46). Puncheon is also preferred over turnpike where firm, mineral soil cannot be easily reached; puncheon can be supported on muddy surfaces better than turnpike, which requires effective drainage.

[diagram] Puncheon
Figure 46—Puncheon

Puncheon resembles a short version of the familiar log stringer trail bridge. It consists of a deck or flooring made of sawn, treated timber or native logs placed on stringers to elevate the trail across wet areas that are not easy to drain. Puncheon that is slightly elevated is termed surface puncheon. Puncheon placed flush with the wetland surface is known as subsurface puncheon.

Sooner or later, you’ll probably hear the term, corduroy. Corduroy is basically a primitive type of puncheon. It consists of laying three or more native logs on the ground as stringers with cross logs laid side by side across the stringers and bound together with wire or nails (Figure 47). Corduroy should always be buried, with only the tread exposed. Corduroy is notorious for not lasting very long and consuming large amounts of material. It should only be used as a temporary measure.

[diagram] Corduroy
Figure 47—Corduroy should be considered a temporary
fix until a more permanent structure can be installed.

Here’s how to build puncheon. First of all, the entire structure must extend to solid mineral soil so soft spots do not develop at either end. Approaches should be straight for at least 3 m (10 ft) coming up to a puncheon. Any curves either approaching or while on the puncheon add to the risk of slipping, especially to stock and to mountain bike and motorcycle users.

To begin construction, install mud sills. These support the stringers. Mud sills can be made of native logs, treated posts, short treated planks, or precast concrete parking lot curb blocks. The mud sills are laid in trenches at both ends of the area to be bridged at intervals of 1.8 to 3 m (6 to 10 ft) (Figure 48). They are approximately two-thirds buried in firm ground. If firm footing is not available, use rock and fill to solidify the bottom of the trench, increase the length of the sill log to give it better flotation, or use more sills for the needed floatation. Enclosing rock and fill in geotextile minimizes the amount of rock and fill required. For stability, especially in boggy terrain, the mud sills should be as long as practical up to 2.5 m (8 ft).

[diagram] Mud sill and stinger layout
Figure 48—Mud sill and stringer layout.

Stringers made from 200-mm (8-in) peeled logs or treated timbers are set on top of the mud sills. They should be at least 3m (10 ft) long and matched by length and diameter. Stringers also need to be level with each other so the surface of the puncheon will be level when the decking is added. Two stringers are sufficient for hiking trails, but for heavier uses, such as stock use, three are recommended.

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