Saturday, August 6, 2011

Benching a New Trail at Whiting

Today was the monthly Friends of Webster Trails work day and a Tryon work day. I decided to work with the FWT group because they have fewer work days and would be working on a new trail I'm very interested in.

There were groups clearing the trail and groups benching. I helped with the benching.

In my trail work with the GROC crew and in the IMBA training, full benching has definitely been encouraged over partial benching, though I didn't know why. Today's trail work got me to look closer.

Here is what the IMBA Trail Solutions book says (page 140-141):
A bench is a section of tread cut across the side, or contour, of a hill. A full bench is constructed by cutting the full width of the tread into the hillside. The entire tread is dug down to the compacted mineral soil. This design creates a consistent and stable tread, but it takes time and effort, since the organic matter that normally covers mineral soil must be removed. In the end, all this effort pays off in the form of a trail that lasts indefinitely with very little maintenance.

On a partial bench trial, o­nly part of the hill is cut away and the soil that has been removed is placed at the lower edge of the trail to try to establish the desired tread width. There are serious downsides, however, to the partial bench design. The section of trail made of fill soil is soft and rarely compacts consistently. As a result, the fill portion of the trail either gradually slips downhill or it compacts unevenly and creates a berm o­n the outer edge of the trail, which traps water. Partial bench trails usually are not sustainable and we rarely recommend this design.

The are a few occasions in which it's simply impossible to build a full bench trail, and you must utilize the partial bench design. It may be impossible, for instance, to dig past tree roots or impenetrable rock in order to place the entire tread on mineral soil. At times like these, you're stuck with the partial bench.
While this logic makes sense to me, it's also logical that no solution is best for every situation. Hal, the president of FWT, pointed out how previous partial benching has held just fine, and suggests that our soil type allows for it. And it is certainly faster to build, so why not take advantage of this technique if we can.

Hal's comments make a lot of sense to me, and the partial benches we did today sure look great.
Anyway, I wasn't sure why full benches were generally considered better than partial, and now I "know". Really knowing will come by observing how our work holds up over time.

Great work today! I'm looking forward to riding this new trail once it's completed.

No comments:

Post a Comment