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DIRT ROADS, WASHBOARDS, AND DUST CONTROL Dust Control Article by Harold Hough February/March 2007 Show me a mine, and I'll show you a dirt road covered by washboarding – those parallel ridges that threaten to play craps with our vertebrae if we drive too fast on them. Although some country residents like washboarded dirt roads because it cuts down on traffic, washboarding at mine sites cost mines money. It can create unsafe vehicle speeds, damage suspension systems, and increase maintenance costs, while sending up clouds of dust that irritate neighbors. It's also a safety problem because a vehicle that doesn't have good contact with the ground can't brake effectively. However, washboards can be eliminated with regular maintenance and a better understanding of the physics behind them. With that in mind, let's look at the phenomenon of washboarding and how to get rid of it. WHAT CAUSES WASHBOARDING Washboarding is the wavelike pattern found on dirt roads. And, although many factors have an effect on it, the main cause is vehicle suspension systems. According to Forest Service people who maintain a lot of dirt roads, your car's suspension system causes the problem when it smoothes out the bumps of the road. As a wheel travels over a bump, the suspension system absorbs the shock and then pushes back against the road surface. On a dirt road, this "push back" either packs or displaces the dirt it hits. As more and more cars go over the bump, the pattern becomes more pronounced. After a while, the familiar washboard pattern occurs. Of course, I hear you asking yourself, "why are the patterns regular?' Wouldn't different vehicles, different suspension systems, and different speeds cause irregular patterns instead of the regular waves? Yes, it would if all things were equal. However it's the drivers who cause the problem. Anyone who travels dirt roads regularly knows that there is an ideal speed to eliminate most of the bumps. If you go faster, or slower, you risk putting your head through the car roof. The ideal speed is the one where your car's suspension system pushes the tires down at the same time there is a depression in the washboarding. Any faster or slower and you are giving yourself a bumpy ride. Naturally the normal driver picks that speed in order to make the ride as smooth as possible. The only problem is that this means the tires are pressing down in the depression and making the washboarding worse. In other words, in order to create a smooth ride, you are making the road worse. SOLVING WASHBOARDING Are there ways to eliminate washboard roads? Yes. The best solution is to build a dirt road that eliminates some of the problem. The road would have good drainage, no large rocks or potholes that create bumps, crushed rock (as opposed to screened or rounded gravel), and enough fines to hold the materials together. Crushed rock tends to lock together better to withstand the action of tires. Unfortunately, that costs money and isn't useful if the road has already been built. This is where dust control agents can help. By binding with the dust in the road, they make the road harder, which reduces the tendency to washboard. They also help keep the fines on the road, which is necessary for a good road. One popular product is lignosulfonates. These products are made from the lignin that naturally binds cellulose fibers together to give trees and plants their firmness. When sprayed on the road, the lignosulfnate solution coats individual road particles with a thin adhesive-like film that binds the particles together. It also allows the particles to bind together closer for a stronger surface that better withstands rain. Unlike other dust control agents, this allows vehicular traffic to resume almost immediately. Unlike petroleum and salt-based products, lignosulfnates are safer to the environment. Foliage and surface water next to the road aren't threatened if the solutions are properly applied. With regular care and a judicious application of dust control agents, mines can eliminate serious washboarding on their dirt roads. Not only will mine employees enjoy the better ride, maintenance costs and dust control will improve. | |||
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