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How to Grade Gravel Roads

By Frank Elswick on 09/19/2017

Soil SementgravelSoil Stabilizationfederal highway administrationgravel roadsgreenpave

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Maintaining a road’s proper shape or “profile” with grading has been historically critical to the health of gravel surfaces. But there’s another way to guarantee longer road life cycles that’s far more cost-effective.

Compared to paved surfaces, unpaved roads are especially susceptible to damage and deterioration of their overall shape. Potholes, ruts, and washboarding can result from prolonged periods of wet weather, while passing traffic kicks up dust and displaces gravel to the shoulder area or even into adjoining ditches.

Keeping unpaved roads in optimal condition comes down to one thing: grading. According to the Federal Highway Administration’s (FHWA) Gravel Roads Construction and Maintenance Guide, an unpaved road should have a crowned surface and shoulder areas that slope away from the center of the road, as well as ditches on either side. This shape, maintained through the process of grading, is critical to proper drainage and moisture control and thus the overall health of the road.

The Fundamentals of Grading

While a motor grader is traditionally used for grading unpaved roads, the FHWA notes that front or rear mounted grading attachments on tractors, rakes, and other devices can be used as well. Regardless of the machinery employed, the aim of grading is always to restore or maintain what the FHWA calls “road geometry,” or the necessary cross-section for a functioning unpaved road.

The operating speed of machinery must be kept low (3-5 miles per hour or less) in order to ensure a good shaping job -- anything faster than that will compromise the quality of the grading. The angle of the moldboard is also important; the FHWA suggests keeping it between 30 and 45 degrees to recover loose aggregate from the shoulder of the road while preventing the material from spilling around the moldboard’s edge. As vehicles pass over the road they often displace road material to the shoulder area, sometimes resulting in potholes and an uneven road surface. Maintaining the proper pitch (the extent to which the moldboard is tipped forward or backward) and angle of the moldboard ensures that the maintenance operator is able to mix this displaced material back in with the surface of the roadway.

A crowned surface is necessary to ensure proper drainage on unpaved roads, but too much crown should also be avoided, as it can lead to an unsafe driving surface. An excessive crown can give drivers the sensation that their vehicle is drifting towards the shoulder area, while an oversized crown on snowy or icy gravel roads can compound the risk of drivers sliding off the road. For these reasons, the FHWA recommends that road managers maintain “1/2 inch of crown per foot (approximately 4 percent) on the cross slope.”

Gravel roads are usually maintained by routine blading and adding gravel where necessary, but sometimes major grading and reshaping is necessary due to prolonged wet weather or unusually heavy traffic. Significant rutting, loss of crown, and deep ditches are all circumstances that necessitate more substantial repair work.

Midwest Helps Gravel Roads Maintain the Appropriate Profile

While motor graders are still used in many municipalities around the country, they are also a costly option. Midwest Industrial Supply, Inc. offers award-winning soil stabilization and natural paving solutions that allow municipalities to keep their roads in good condition -- without breaking their budgets. Soil-Sement® Engineered Formula utilizes high performance, critical application polymer emulsion to give exceptional dry and wet strength properties and strengthen road surfaces. Patented GreenPaveTM natural paving system employs alternative binders to create road surfaces as strong and durable as pavement out of native soils. GreenPave’s application also increases loading capacity (CBR), improves the structural integrity of the road, reduces the need for frequent grading, and lowers long-term maintenance costs.

While traditional grading might not always be feasible, Midwest’s products ensure that road managers around the world can keep maintenance costs down and keep their gravel roads in prime condition every day of the year.

About Author

Frank Elswick

Written by Frank Elswick

Frank is the sales unit manager of Midwest's road construction, natural paving markets.

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