By Claire Pendergast
Tip 2: Proper Gravel Material to Re-Surface Your Camp Road
Road material is comprised of three basic types: gravel, sand, and fines. Gravel and sand particles are coarse material. Fines (silts and clays) are generally comprised of particles too small for the eye to see. Coarse material provides strength — the large voids between the particles provide good drainage. Fines fill the voids between the coarse material particles, holding them together, and on the road surface decrease infiltration of water into the road.
It is critical to keep water out of the roadbed. An ideal roadbed has two layers: a base layer that provides strength and is free draining; and a surface layer that is strong and dense, shedding rainfall and preventing it from infiltrating into the bed. When selecting roadbed material, it is important to have a range of different sized gravel and sand so that the particles “lock” together. If they are all the same size, they are more apt to move around, causing rutting. The specific composition of soil materials used in camp road construction makes a big difference in performance and durability. Good road material should contain portions of each type of soil material.
Road base material needs to be sturdy and drain freely. Use gravel that is coarser than the road surface material and consists of well-graded gravel smaller than 3,” but which may contain a few larger stones no larger than 6”. The base material should be no more than 7% fines (silt-clay particles), to allow for subsurface drainage. The base layer should be 12-18 inches thick when compacted. Road surface material needs to pack well, be durable, and shed water. Road surface material should consist of well-graded gravel, with the majority smaller than 1/2” and a maximum size of 2 “; and contain 7-12% fines (silt-clay particles), so it packs well and sheds water. The surface layer should be about 4 to 6 inches thick when compacted.
For additional information regarding Camp Road Maintenance, see https://www.maine.gov/dep/land/watershed/camp/road/gravel_road_manual.pdf
See additional articles in this series here: https://www.keokalake.org/post/camp-road-maintenance-series
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