Washboards in Dirt Roads

[Fat_Charlie_the_Archangel]

Does anyone know what causes ‘washboard’ bumps in dirt roads? They are obviously caused by tires, but why do they go all the way across the road (where tires don’t normally go)?

[Duck_Duck_Goose]

Have I ever mentioned how much I LOVE the Internet?

Google, “washboard road causes highway maintenance”. Everything You Always Wanted to Know About Washboard Roads But Were Afraid To Ask…(too long to quote or Biblio will edit me :eek: )

http://www.t2.unh.edu/summer99/pg3.html

Why Does It Happen?
Similar to the asphalt top course on paved roads, gravel is the “wearing surface” of an unpaved road. The large stones, in contact with each other, distribute vehicle loads to the road base beneath it. The stones are held by smaller particles, especially “fines” which pass a 200 sieve (a screen with 200 wires per inch). With insufficient fines, vehicle tires more easily move the stones. As their particle-to-particle contact decreases, so also does their ability to distribute loads…

Go. Read.

[robinh]

Damn, DDG…I know it’s been said before, but I stand in awe of your Googling skills.

[Fat_Charlie_the_Archangel]

Went. Read. Didn’t find answer.

The article does talk about washboard roads, but it DOESN’T answer my question. I understand that car tires force the gavel, rocks, etc. around on a road’s surface, but why do they align in rows like waves? And do those ‘waves’ connect across roadways even in areas where tires don’t usually pass?

[Turbo_Dog]

Try this one, Fat Charlie

http://www.gi.alaska.edu/ScienceForum/ASF12/1291.html

[q]Bumps in the road surface cause the tire to hop in the air. When the tire crashes down, it forms
valleys by spraying sand and gravel forward and sideways. The moving tire ramps out of the valley
and hops again. Thus, the washboarding process repeats itself.[/q]

[TheLoadedDog]

Australia’s answer to Cecil Adams, Dr Karl Kruszelnicki has this to say about road corrugations (or “washboards”, as you 'merrikans call 'em). Come to think of it, he also had this to say, as well as this. Oh yes, and this.

[TheLoadedDog]

To save you the trouble of wading through all those links I gave above, here is a theory regarding the appearance of corrugations across the entire width of the road (the part I have italicised… -the er… text, not the road ):

… corrugations on a dirt road are simply small sand dunes. The action of a car driving over the road at speed causes wind to blow across the dirt particles, just as on the beach, and relocation of the dirt particles occurs to form small indentations in the road. When the next car drives over the road, the dirt particles that are blown by the car generated wind may be subject to the action described in (c) above. The process will continue and form small “dirt dunes” i.e. corrugations in the road.”

Lloyd Junor, who has spent many years travelling the Outback, agreed.* He also pointed out that, “Corrugated roads have the corrugations road-wide, not precisely where the vehicles’ wheels traffic them. So traffic does not explain the corrugations.

The wind is the culprit for corrugated roads. (Admittedly helped by traffic, which may loosen some surface materials.) The wind moves the looser earth, piles it up, and lo and behold, an untrafficked road is corrugated without ever having seen a vehicle since being graded.*

An item you may care to alert your listeners to: the wind builds the corrugations in the shape of an inverted saw-tooth pattern, the steep ramp being on the lee side. (Dunes are built the same way). Vehicle traffic can accentuate this shaping. That‘s why at times (when out in the scrub, and no-one around for ever, therefore safe to do so) an Outback driver will go to the opposite side of the road to experience a less jarring ride.”

I have been given a lot of theories. They all seem to have an element of truth in them. I reckon that the only real way to pick between them is to do experiments to test them.

[tisiphone]

Some of it is also caused by the grader operator making a mistake and chattering the blade on down the road. I’m surprised the Alaskan link didn’t seem to mention this - it seems to be a regular feature up North. Or maybe it’s just our crews.

I got this off some of the guys who work highway maintenance in the Yukon.