Saturday, May 22, 2010

Building a Forest Trail


Once your community group has got permission to build a trail in a public forest, you should read a good trail building manual. The following is an excellent guide from the US Dept of Transportation:Trail Construction and Maintenance Notebook 2007:

The guide encourages innovation and using your head to find the best solutions for the conditions and materials at hand. While BC has a considerable variety of soil conditions, it is quite common to find a trail location on a steep side-hill in soils that have considerable rocks and boulders and little fine materials.

The typical approach to building a trail in rocky soil on a steep side-hill in BC has been to bash a way through by excavating a bench in the side-hill. Little effort is made to rearrange the materials . Large rocks are left in the trail tread or walking surface and scarce fine material is wasted down slope. Once the trail is used, the larger rocks will project out of the surface creating tripping hazards. Hikers tend to avoid these hazards by walking around them often breaking down the outer edge of the trail in the process.

The trail in the photograph above is on a 100% side slope. It is half bench construction. The rock from the excavation is used to make an outer drystone retaining wall and the fine material is retained to make a trip free walking surface. This method much reduces the excavation and bare soil cut slopes.

Constructing a half bench drystone retaining trail on a slope does not require great skill. Most approach the task thinking that great skill is required to fit uneven pieces of rock to provide a stable structure. First you cut a key into the slope to take the first row of large rocks. Additional layers of rock are roughly placed on top. With each layer of outer large rocks, fill behind with smaller rocks and stones. It is these smaller rocks that add friction and stability to the structure. Finish the trail surface with the finer soil material.

Tools needed are a mattock for excavation, a 12 lb sledgehammer and a steel pry bar to deal with rocks. A wheel barrow and a shovel to end haul scarce fine material is also most useful.

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