Mud claps

Roads & Bridges / April 02, 2008

It happens every year like clockwork. The precise time varies from March to June depending on your location and elevation. For many road crews, the spring thaw signals the end of winter and the beginning of spring grading season.

This brief period of time is especially critical for dirt and gravel roads, because spring grading operations prepare the road surface for summer traffic by:

  • Rebuilding a proper surface structure to shed road drainage; and
  • Reintegrating road material to reduce dust generation.

To truly understand how important spring grading is for the road throughout the year, winter’s effects on the road must be understood. Several conditions occur during winter months that trap excess water in the road. Roadside plants and trees that normally pull groundwater from the road area are dormant during winter, leaving roadsides saturated with excess water. The freeze-thaw cycle further saturates the road by drawing large amounts of water upward through capillary rise. As the road thaws from the surface downward, water becomes trapped between the road surface and underlying frozen soil. With even more water added from melting snow and seasonal rains, spring is the roughest time of the year for an unpaved road. The good news for road maintenance crews is that during “mud season” this excessive spring moisture is, ironically, the key to repairing the road during spring maintenance.

As the road thaws and begins to dry, it creates ideal grading conditions because the road is uniformly wet. Uniform moisture throughout the road profile—from the road base to the road surface—is crucial to proper grading. Sustained rain events or even hurricanes at other times of the year will not have the same effect. This top-to-bottom moisture will lubricate road particles and allow them to be moved more easily during grading operations. Proper moisture also prevents aggregate segregation by size, as would happen in the grading of dryer material. And, lastly, proper compaction of the driving surface can be achieved when adequate moisture levels exist throughout the entire road structure.

Let it berm

The initial spring grading is the first and best chance road maintenance crews have to salvage berm material from the edge of the road. Berm material is road material that has been pushed to the side of the road by traffic and winter maintenance activities. It is important to incorporate this valuable road material back into the road surface during spring grading. The grader (or drag) that is being used must be able to cut into the berm material, move it onto the center of the road and mix it with the existing road surface material.

Once again, the ideal moisture levels present in the spring aid in this process of reincorporating berm material, because grading equipment can cut deeper into the existing road surface to loosen the fine material and reincorporate it with the larger berm material. This mixing of berm and road material is achieved by allowing material to ride up the grader blade and roll back onto itself several times. This repeated mixing effectively integrates the larger berm material with the loosened fine road material. Without uniform moisture to adequately lubricate all road materials and prevent segregation by particle size, this task would be nearly impossible.

Taking a bite out of dust

Spring grading also plays an important role in dust reduction throughout the rest of the year. Many roads consist of purchased hard aggregate placed over a much softer native material. The greatest maintenance benefit in road stability and longevity occurs when the purchased hard stone remains incorporated into the road surface. When the larger stones of purchased aggregate become loosened on the road surface, traffic causes them to migrate toward the edge of the road and collect in windrows. As these harder stones ravel across the softer road material under the abrasive force of traffic, they grind against the road surface. This perpetual grinding creates more and more loose, fine material that is readily available to become fugitive dust.

Significant windrows of loose stone along the edge and centerline of the road is a clear indication that the road needs to be graded. To avoid the road degradation and dust generation that results as road material is loosened by traffic and travels back to the raveled windrow on the road edge, adequate road compaction is crucial.

Pull behind to get ahead

Road compaction is often the most overlooked component of sound road maintenance. Too many maintenance organizations rely on traffic alone to compact a freshly graded road. Unfortunately, this practice is counterproductive, because it speeds up the creation of unwanted (and expensive to repair) road rutting. Traffic tends to run the same path over and over. This compaction in the driving lanes destroys the road crown that spring grading operations just worked to achieve. To prevent the loss of road crown and lengthen maintenance cycles, the road should be uniformly compacted after any and all grading operations.

For necessary compaction, a simple pull-behind static roller will work wonders. In cases where compaction equipment is not available, articulating graders can be used to compact the road. Articulating graders can offset the front and back tires to widen their wheel track across the road. A few parallel passes over the recently graded road segment will help to compact recently incorporated road material, set the crown and reduce the frequency of future maintenance efforts.

The importance of spring maintenance in preparing roads for year-round use cannot be overstated. Many road-maintenance professionals take advantage of the moisture levels available in the spring to address many common problems such as potholes, washboarding and severely misshapen roads. Mud season does not last forever, but neither does the window of ideal grading conditions. So “strike while the iron is hot,” or better yet, “grade while the road is wet.”

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