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Making Washboard Roads

01/11/2025 2:37 PM

Traveling around in the countryside on dirt roads and sections of road that are minimally maintained, you often find sections of road that has that washboard texture that can rattle you and the vehicle to pieces. I normally found these sections on grade changes in the road or approaching stop signs or intersections. My initial thought was this annoying surface was simply from the physics of vehicle traffic slowing down (or speeding up) and since the dirt is elastic to a degree, it simply stretched out or bunched up.

So when we had a section of road in front of our office redone I noticed something similar that had me question this theory. The roadway is a dead end street/road that is in a rural/residential area. We have some heavy trucks using the road but mostly small trucks and passenger cars to the homes and offices. All traffic is low speed, 30 MPH or less. The section that was refinished is 1/4 mile or 400 meters and is completely flat, no grade change. The section was graded and rolled, and quite smooth. The next day they added a layer of gravel but I don't know what other preparations were done. The road is wide enough for two lanes plus some extra.

Within a week the entire stretch became a torturous washboard that rattled your teeth loose. What intrigued me was the uniformity. The washboard lines went straight across the width of the two lanes. The spacing was fairly uniform at 15- 18" (38-35 cm)

So is the spacing due to the average circumference of the tires used on the road? The speed of the vehicle? and why a straight line across the whole roadway. Is the gravel setting up in that fashion because of resonance created by vehicle vibration on the road surface, (similar to when salt or sand resonates on a plate vibrated by a speaker)?

Or is it something else all together, or a combination of these and many other factors.

This is in the southwest US. There was and has been very little rain (I'd say less than an 1", and none during the time this incident occurred)

Apologies, I couldn't get this photo to display properly and I couldn't get good resolution with my camera, but you can see a bit of the ridges and pattern as you approach the end of the repaired section

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#1

Re: Making Washboard Roads

01/11/2025 5:58 PM

"Ridges on unpaved roads, often called "washboarding," are primarily caused by the repeated action of vehicle wheels rolling over loose gravel or dirt at a certain speed(too fast), which displaces the material and creates a series of ripples in the road surface, similar to the pattern on a washboard; this phenomenon is most prominent when the road material is dry and loose, with factors like poor quality gravel, high vehicle speeds, and lack of road crown contributing to the issue. "

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#11
In reply to #1

Re: Making Washboard Roads

01/14/2025 8:54 AM

Base on the phenomenom regard the "equilibrium" of the materials used in roads construction… all of them (the materials, meaning dirt, sand, gravel) found that equilibrium forming a piramidal profile.

Those materials, to avoid any deformation needs to be bound.. Not losse.. Otherwise, nor only the loads, but the "outdoor influene" like wind, can create that deformation.

Look at the desert… it happen the same… without any external loads.

I still can not attached images.

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#2

Re: Making Washboard Roads

01/11/2025 7:40 PM

Depending on the location, look at the history. We had a road that was called the locals called Corduroy Road. The towns official name was Quarter Line road. It was black graveled at the time and later on black top.

i asked my parent why the two names. Well the road ran through a swamp. And what they would do, when building the road, in the low wet areas, is lay logs down across the road side by side and then filling in.

that’s when I noticed how the roads were wavy between what was the original logs.

hence the name Corduroy because the road looked like the fabric.

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#3

Re: Making Washboard Roads

01/11/2025 8:24 PM

I'm sure there are multiple things going on and multiple answers that share an element of "correctness".

As a kid, when we went over roads like this, my father would say that the roughness was caused by the grader's blade bouncing.

As the grader transitions from a totally dirt road to a totally paved road there would often be rock, pavement chunks, or other debris to increase the bounce of the blade. In these transition regions the operator would also be making numerous adjustments trying to grade the dirt down, but not rip the pavement up. Thus, often extra bounce in the transition region.

You will often also "washboard" on an asphalt road approaching an intersection. This can be caused by the momentum of heavy trucks squishing soft asphalt forward while stopping on a hot day.

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#4

Re: Making Washboard Roads

01/11/2025 8:41 PM

Here is an explanation that seems plausible:

"While driving Alaska’s graveled highways, countless people have no doubt wondered about how an unpaved road surface turns into a bouncing bed of corduroy. Keith Mather, who was studying nuclear physics in Australia in the early 1960s, had the same question. He wrote a paper about washboard roads in 1963."

He set up an experiment and reproduced the effect.

"Bumps in the road surface cause the tire to hop in the air. Where 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."

https://www.gi.alaska.edu/alaska-science-forum/removing-mystery-washboard-roads

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#5

Re: Making Washboard Roads

01/12/2025 5:31 AM

Really it is mostly to do with the skill of the grader operator. Have you ever worked in a mine, I have and the skill of the finishing grader operator who adjusts the angle of the blade as he goes to wipe out these wash boards.

Imagine driving a 830,000 haul truck over was washboard road it would soon break up.

Between the grader operator and roller driver they can produce a road that a 4x4 can drive along and share with these behemoths and not shake and rattle. Civilian roads are built to a price by poorly trained operators without pride in their work. A lack of correct compaction and improper finishing soon shows up in the finished product.

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#6
In reply to #5

Re: Making Washboard Roads

01/12/2025 2:11 PM

Ah, the joy of driving washboard road sections pulling a horse trailer.

The cause of this so called washboard road effect has been revealed in an article in the January 1963 issue of Scientific American.

My takeaway is, eventhough not plainly stated, gravel and dirt roads washboard... because they do.

A washboard type of effect can occur in railroad tracks. This is not discussed in the SA article.

Another recent thread subject was suggested as a thesis subject.... Just sayin’.

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#8
In reply to #6

Re: Making Washboard Roads

01/13/2025 7:04 AM

<...A washboard type of effect can occur in railroad tracks....>

It does indeed. Over here it's called "cyclic top".

It can be cured by a combination of tamping

and rail grinding.

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#9
In reply to #6

Re: Making Washboard Roads

01/13/2025 11:45 AM

A more recent Scientific American podcast discusses the inevitability of washboard roads. It is only a minute-long audio so they don't go into too many details.

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#7
In reply to #5

Re: Making Washboard Roads

01/12/2025 4:59 PM

It’s like any other skilled labor.

you order 11 years on concrete, and the driver asks how you want it, and you say 4”. He lays it out 4” thick and you do very little pushing and waiting for the next load.

next load you tell the driver same thing, and you got 1” and then a pile 6-7” and then 2”. And your still pushing concrete when the 3rd truck pulls in.

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#10

Re: Making Washboard Roads

01/14/2025 6:03 AM

Here is a link to studies on the subject:

https://en.wikipedia.org/wiki/Washboarding

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#12

Re: Making Washboard Roads

01/14/2025 8:58 AM

Here an interested meme that somewhat questions modern road building.

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#13

Re: Making Washboard Roads

01/16/2025 6:10 AM

Washboarding, (or corrugations down under) are inevitable on formed unsealed roads. It is unlikely to relate to grading since the blade is at an angle to traffic direction during normal working of the materials.

Also happens on corners and is usually more noticed on the inside of the corner due to higher scrubbing forces.

The wavelength has a strong relationship to the dominant vehicle speed.

Dry environment enables changes to the bulk material mix, with the very fine portions leaving as dust plumes. Those fines are the primary binders with modest water content.

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#14

Re: Making Washboard Roads

01/16/2025 9:13 AM

An easy way to picture what is happening is to compare the loose gravel to water.

As tires move through it, they push gravel ahead, just like a water wave, and they move across the surface just like water, albeit slower. The spacing of the waves depends on the traffic speed. A slower speed will result in longer distances between the waves.

Once the first wave builds up, the rest is simply play "Follow the leader" as the wheel "Hop" on the new "Bump" amplifies the previous one.

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#15

Re: Making Washboard Roads

01/22/2025 12:53 PM

Friend,

I recall reading an article on how washboard roads are created, in an issue of Scientific American magazine around 30-50 years ago. It is not cited in the Wikipedia article on this.

--JMM

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