Better Roads Digital Magazine
Issue link: https://read.dmtmag.com/i/102915
Unpaved Road Preservation While preservation of asphalt and concrete pavements has become quite technically advanced, preservation of unpaved gravel, stone or dirt roads is still at the maintenance stage, in which preservation is defined as preventive maintenance. South Dakota has articulated a checklist for preservation of its many miles of gravel roads. Blading and graveling of mainline roadways and shoulders are effective at reshaping or replacing granular material lost on the surface of either a roadway or shoulder, the SD DOT says. "Graveling of mainline or shoulders involves shaping of the surface and a periodic addition of granular material to provide a smooth driving surface or shoulder that has a proper crown slope and is free of ruts and distortions," it maintains. Deficiencies include: Rutting and shoving of material. Wheel motion of the traffic will shove material to the outside (as well as inbetween traveled lanes), leading to rutting, reduced water-runoff, and eventual road destruction if unchecked, the state says. As long as the process is interrupted early enough, simple blading is sufficient, with material being shaped to correct the deficiencies. Washboarding. Washboarding is the formation of corrugations across the surface at right angles to the direction of travel. They can become severe enough to cause vibration in vehicles so that bolts loosen or cracks form in components, the DOT says. Blading performed under the correct moisture conditions will aid in removing the corrugations, and the addition of a good quality gravel can help prevent them reforming. Cross slope. The amount of crown in the roadway or shoulder should be maintained at a rate of 0.3 foot per foot, to 0.05 foot per foot. This amount of crown will allow for adequate drainage of surface water without washing off surface materials, South Dakota says. Loss of fines. If a gravel-surfaced roadway or shoulder has dust blowing off the surface, it indicates a loss of fines, and material is being lost, causing the road to deteriorate. "Typically a roadway with average traffic loses about 1 inch of material per year," the state says, "so periodic replacement with good quality material is a necessity." Blading and reshaping of a roadway or shoulder should take place in moist weather conditions if possible, the South Dakota DOT says. "When blading, material should be pulled from the in-slope area back up onto the roadway or shoulder surface and smoothened, watered, and compacted to the proper grade and crown slope. The grader should be operated at a top speed of between 3 to 5 miles per hour, and the grader moldboard should be operated at the correct angle and pitch to adequately move and mix the material. Inventory, Plan in Washington County Maintenance of unpaved or gravel roads in a jurisdiction can be addressed in a systematic method, as Washington County, Iowa – located just west of the Quad Cities – did recently. Beginning in 2008, when a "perfect storm" of diminished cash flow, increasing traffic and loads, and excessive flooding severely damaged many unpaved roads, the county's engineering staff prepared a $12 million, multi-year unpaved road improvement program funded largely by an $8 million general obligation bond issue that county engineers were able to justify with the plan. "High costs and flat revenues, increased vehicle weights, and increases in rural traffic volumes have created conditions on the gravel road system in Washington County that are quickly becoming unacceptable to residents," said David Patterson, P.E., Washington County engineer, in September 2008. "While any one of these changes – financial, increased weight, or traffic issues – could probably be handled by the system under its current allocation of resources, the combination of all three has tipped the system into a downward spiral that will become irreparable if changes are not made," Patterson said in terms that are familiar to the pavement preservation community. "Under its current allotment of resources, the gravel road system has reached a point where damage is being done faster than can be repaired." This plea was buttressed by an unpaved roads inventory. "During the summer of 2008 the Secondary Roads Department performed a complete inventory of the gravel road system in the county," Patterson said. "The inventory marked the condition, needs, and noted any special circumstances of every gravel road in the county." A comprehensive review of the available solutions was then performed to see what solution would best apply to which road. These solutions included adding rock surfacing, grading the roadway to repair deficiencies, upgrading a roadway for paving, or vacating/downgrading the road classification. As articulated in 2010, Patterson outlined four outcomes for bringing county unpaved roads up to par: Fix the six to eight "hot spots" where the county spends three to four times its average maintenance dollar (average of $2,500 per mile, compared to $7,500 to $10,000 per mile in these locations) Make system-wide improvements to gravel Better Roads January 2013 17