Thread: How do corrugations form?

I always thought that corrugations across the road were caused by consecutive long term ant crossings ....................



The more ants there are in the area, the closer together the corrugations.

But I've since found out .................................................. ..

that it's really the grader steerers that are causing the problem.



I think this is LandyAndy's grader below ...........................

Corrugations

CORRUGATIONS 2

Baz.

Here's how I beleive they are created.

No road is ever perfectly flat. There will always be an imperfection.

Wheel rolls along, hits a bump.

Wheel is bounced upward, part of the energy is tranfered to the vehicle and it moves upward slightly, remainder of the energy is absorbed by the spring in the suspension.

Wheel passes over the bump.

No matter what there will always be a delay while the wheel changes direction from moving up toward the vehicle to moving down toward the ground.

During this delay, weight is reduced on the ground, possibly to the point that the wheel loses contact with the ground.

This means small particles of dirt that were being rolled across the ground by the tyre are left on the trailing edge of the bump. So the bump grows bigger.

The wheel then moves back toward the road and then this movement gets stopped by the road. As this movement is stopped, more force is exerted between the tyre and the road.

This extra force moves a little more particles of dirt creating a slight lower point from both removed matter and a little extra compaction.

The next wheel to roll over this point now has a larger bump followed by a low point and then another small bump. This wheel makes the first bump a bit larger again and the dip a little deeper and the following bump a little higher and the next thing you know these go on and on.

These are made worse during braking and accelerating because the wheels are excerting more force on the road so they more move dirt.

Happy Days.

Here.

so if we had solid suspension and solid wheels there would be no corrigations,can't say i have seen fred flintstone driving on corrigations.

When I was a young bloke and living in Winton in the 50's there was barely a sealed road west of Rockhampton other than main streets and concrete bottoms on fords. Many of the old bush drivers reckoned corrugations were formed by the characteristics of independent suspension. I have no thoughts on the matter. Just threw that in to start some conjecture.

I was told years ago by an engineer that it is the road material congregating around a Standing Wave (a harmonic vibration) caused by the vibrations created by all vehicles. These vibrations create a Sine Wave (high and low spots) and when they come together to form a harmonic, you get a standing wave....like you may have seen in science at school using a water tub.

I was driving in a RAAF 110 Defender with him at the time and he was explaining it as we crossed some really bad corrugations. To further support his theory he pointed out that they become more extreme as the dirt road meets a harder surface, like a sealed section of road or concrete at a bridge, etc. Though and behold, as we approached a concrete bridge section on the dirt road, you could literally see the road material dancing in ripples (waves) as we got closer to the bridge but they (the waves) weren't moving .... the ridges were static. There was less or no material bouncing in the low spots, mainly the high.

That doesn't mean there are always going to be bad corrugations at bridges, etc. The permanence of the ridges are dependant on a lot of variables like the material the road or track is made of, the surrounding ground density, etc.

The theory sound pretty reasonable to me.

What other guys are posting about suspension systems and tyres bouncing on existing lumps, etc are probably accurate, as this vibration would just add to the waves that would form regardless.

On softer surfaces, I think wind would be a factor all by itself and would also contribute to the vibration based situation. This would explain deserted tracks having ridges too. An accelerated example of this would probably be a beach on low tide on a really windy day.....they ripple up very quickly. The East Coast of Moreton Island is always very windswept and it has undulations and ridges everywhere. So a different cause than vibration but you can see that it could still be a factor.

Cheers,

Kev.

In case no-one has already posted it, here's Dr Karl on corrugations.

Karl Trek -Corrugated Roads Revisited

Basically similar to what Joel posted earlier.
Wheels hop over small rises and then land and spray the road material, so the corrugations get bigger and bigger.
Vehicle speed and the hardness of tyres seem to affect the rate of formation.
That's all I've got, maybe others have better ideas.