Powdermill Nature Reserve
French Mattress Driveway
The methods used during the installation of the driveway were a bit different from those used to construct the water-permeable parking lot. French Mattress technology was used where the driveway crossed two small drainage ways. The French Mattress, made up of coarse rock wrapped in a water permeable fabric, is used to provide road support and to maintain subsurface water on both sides of the road. Large rocks in the lower part of the French Mattress provide support strength while smaller rocks near the top help to distribute the weight of vehicles. Fine materials such as contaminants are trapped in the spaces between the rocks as the water gently filters into the soil.
Several types of stone were used to top off the French Mattress, including a crushed stone called driving surface aggregate which is designed to maximize packing density on the driving surface. The French Mattress was installed with the help of the Center for Dirt and Gravel Roads.
The benefits of French Mattress installation include corrected road support, natural equalization of subsurface water on both sides of the road, very little maintenance, and a gentle, non-erosive water discharge. Not only are these construction methods environmentally sound, but they also help to minimize cost and reduce future maintenance demands.
The Finished Product