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Trail Construction and Maintenance Notebook

Trails in Wet Areas (continued)

Puncheon (continued)

Notch the mud sills, if necessary, to stabilize the stringers and to even out the top surfaces (Figure 49). To hold the stringers in place, toenail spikes through the stringers to the mud sills or drive Number 4 rebar (1/2 in) through holes in the stringers.

[diagram] Puncheon assembly
Figure 49—When using logs, notch the mudsill—not
the stringer. Do not notch them more than one third
of their diameter.

Next comes the decking. The thickness needs to be strong enough for the loads the structure will need to support. Lengths can be as narrow as 460 mm (18 in) for a limited-duty puncheon for hikers. The decking should be 1.2 to 1.5 m (4 to 5 ft) long for puncheon suitable for stock use.

Do not spike decking to the center stringer, if you have one, because center spikes may work themselves up with time and become obstacles. Leave at least a 20-mm (3/4-in) gap between decking pieces to allow water to run off (Figure 50). Decking should be placed with tree growth rings curving down. This encourages water to run off rather than soak in and helps to prevent cupping.

[diagram] Puncheon assembly
Figure 50—Place decking planks on stringers to
provide bearing for the full width of the plank.

Running planks are often added down the center for stock to walk on. Often the running planks are untreated because horseshoes cut out the plank before wood has a chance to rot. Do not leave gaps between running planks because they can trap mountain bike or motorcycle wheels.

Curb logs, also called bull rails, should be placed along each side of the puncheon for the full length of the structure to keep traffic in the center. To provide for drainage, nail spacers between the curb logs and the decking.

Finally, a bulkhead or backing plate needs to be put at each end of the structure to keep the stringers from contacting the soil (Figure 51). If the plate stays in place, do not spike it to the ends of the stringers. Spiking causes the stringers to rot faster.

[diagram] Puncheon assembly
Figure 51—Place a bulkhead or backing plate at each end
of the puncheon. Approaches should have a rising grade
so water will not run onto the structure.

In the rare case where puncheon is constructed on grades steeper than 5 percent, treat the surface to reduce slipping. Use cleats, commercial fish netting, mineral roofing, or other surfacing.

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