Re: Definitive Washboard Protocols
Posted by Zardoz on July 08, 2003 at 11:32:08:
In Reply to: Re: Definitive Washboard Protocols posted by Harold Ericsson on July 08, 2003 at 11:16:10:
Why Do Roads Corrugate?
This article is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Larry Gedney is a seismologist at the Institute.
Corrugations that produce washboard roads are not limited to those with sand or gravel surfaces, but are also found in asphalt pavements and even in railroad tracks, although on a less severe scale.
It would seem that such a common phenomenon should be readily understood and explainable, but the fact is that the process which produces them was a subject of controversy among engineers for many years. One of the most popular theories was that a tire, even as it rolls, pushes material ahead of it in a heap. Once the pile reaches a certain size, the tire rolls over it and starts the process again. As it developed, this is incorrect.
The January 1963 issue of Scientific American contains an article by Dr. Keith B. Mather, now Vice Chancellor for Research and Advanced Studies at the University of Alaska, which puts the matter to rest once and for all.
Working at the University of Melbourne, Mather observed that vehicles passing over the unsurfaced roads of Australia's "outback" did not produce dust uniformly even on uncorrugated roads, but rather in little spurts arising from rapid bouncing of the wheels.
This led to the construction of a laboratory apparatus which would permit the observation of wheel and road interactions under controlled conditions. The first experiments utilized a five-inch wheel mounted on the end of a shaft which pivoted about the center of a sand track 24 inches in diameter. Locomotive forces were provided by pushing the arm around the track with a finger. Unexpectedly, this soon produced little corrugations several inches apart in the sand.
Encouraged by these results, Mather then proceeded to construct a somewhat more elaborate system equipped with a variable speed electric motor, which drove the axle, a spring-mounted wheel and a revolution counter. Parameters such as weight, size of wheel and stiffness of spring were made independently adjustable.
Among the more significant findings were that:
If the wheel moves slowly, no corrugations were formed, but a deep rut instead;
Corrugated roads would be all but eliminated if people followed two simple rules. First, they must let most of the air out of their tires (hard tires corrugate roads faster), and second, they must be willing to travel at less than ten miles per hour. Since it seems unlikely that either of these guidelines would be followed, the only thing that remains is to construct all rural highways out of three-foot-thick reinforced concrete--not a likely prospect for the foreseeable future.