The Bridge, Winter 2015-2016
Cassandra Matchinski, Technical Writer
Article re-printed from Iowa LTAP’s adaptation of
Caterpillar’s Governmental Solutions, Spring 2012.
Like fingerprints, each unpaved road is unique. The wear surface may be gravel, crushed rock, or sand, but all have one thing in common: maintenance is required to keep the roadway in good driving condition. Traffic displaces road surface material onto shoulders and into ditches, forming ruts in the roadway. Wash-boarding forms at stop signs, hills, and turns, and in areas of acceleration or braking. Storms, runoff, and snowplowing also take their toll on unpaved roadways.
Following are 12 tips that can help motor grader operators to lengthen road maintenance intervals and avoid rework:
1 To remove wash-boarding, cut the corrugations to their full depth, then regrade the area with moist material that will compact. (Corrugations filled with loose, dry materials will reform quickly in areas of high vehicle traffic.) Corrugations are best removed using a scarifier or a serrated cutting edge.
2 Articulating the rear frame toward the toe of the moldboard by 2 to 5 degrees helps reduce motor graders’ tendency to bounce, and is extremely effective when cutting out washboards. This places one front tire slightly ahead of the other, allowing one tire to be on top of a corrugation while the other is in the
bottom. As the tires roll up and down through the washboard, the front axle will pivot up and down, keeping the front mainframe stable. Don’t use the crab mode when scarifying wash-boarded areas, as this can bend the scarifier shanks and/or linkage.
3 Cut to the depth of major potholes to eliminate them. (Again, filling holes with loose, dry material is ineffective, as traffic quickly displaces the loose material and the holes reform.)
4 Typically, begin road maintenance with the moldboard top approximately 2 inches ahead of the cutting edge, and then adjust to the material and conditions. Tip the moldboard forward or back to obtain and maintain the desired cutting-rolling action. Tipping the moldboard forward will increase moldboard throat clearance. Generally, a wider throat opening allows better material flow along the moldboard in a wide variety of soil types. Maintaining a rolling action on the material while working reduces the horsepower required and provides maximum productivity.
5 Material buildup in the circle area may increase circle wear. It can also stop material rolling action and cause it to be bulldozed. Bulldozing material requires more horsepower and more traction and reduces motor grader productivity.
6 Apply only enough downward pressure to accomplish the task. Excessive downward pressure on a hard, dry surface causes rapid cutting edge wear, requires more horsepower and fuel, and reduces productivity.
7 The blade’s tip angle should be positioned with the cutting edge at 90 degrees to the road surface. In this position, downward pressure on the moldboard places less stress on the cutting edge and retaining bolts. The edges also tend to ride over objects, which helps prevent machine damage.
8 For maximum machine stability when maintaining roadways, the motor grader’s main frame should be straight with the drawbar and circle-centered under the frame.
9 For the widest possible pass on the travel surface, keep the moldboard angle as square to the frame as possible. If material starts to flow around the leading end of the moldboard, or the rolling action dies, increase the blade angle.
10 Keep machine travel speed as high as possible for maximum productivity but low enough to prevent machine bounce (generally, 3 to 5 mph).
11 Moldboard angles of 10 to 30 degrees are normally used in light, free-flowing material. Higher moldboard angles of 30 to 50 degrees are required when processing wet-sticky material, mixing large windrows, and ditching.
12 To cut hard material or for finishing work, tip the moldboard further forward than the start position. When finishing, tip the moldboard top 4 to 5 inches ahead of the cutting edge so the cutting edge is approximately 90 degrees to the cut surface. This moldboard tip position will generally position the drawbar parallel to the finished grade. As always, road conditions and your fleet are factors in your agency’s road maintenance practices.
The 2015 FHWA Gravel Roads Construction & Maintenance Guide is now available! The Center for Technology & Training will be sending a copy to every county road commission, and there will be 20 additional copies available for cities, townships, and villages on a first come, first served basis. The electronic version is available here:
The Motor Grader Operator’s Training Manual developed by Michigan LTAP is used in motor grader training throughout Michigan each year. In addition to gravel road maintenance, the manual covers parts of the road, dust and erosion control, and safety procedures.