4WD MODIFICATIONS - TECH TORQUE
We’ve read many theories on why corrugations occur, but Outback Travel Australia’s conclusion is that nobody really knows. Also, corrugations occur on river beds and on coastal shores, on asphalt and concrete roads, on railway lines and in the atmosphere.
Everyone who’s driven off the black top knows what driving on corrugated sand and gravel roads feels like and we’ve given you some driving tips on how to deal with them.
However, we’ve been asked by many people what causes these literal pains in the arse.
The result of our global research into this topic is that, in 2023, no-one really knows what causes this rippling phenomenon and a great deal of money is being invested in finding a cure – if there is one. You see, for us in the outback travel world it means merely discomfort and delay – and possibly some vehicle damage – but for other people dealing with corrugations on various surfaces, it’s much more critical.
The important factor is to understand that probably every theory you’ve read about the cause of corrugations on unsealed roads is wrong. By far the most popular one is that they’re caused by displacement of loose surface particles into ripple patterns, with typically 300-600mm wavelength, but how can that be true when corrugations regularly occur on surfaces that aren’t loose?
Bitumen road corrugations
There are many sections of bitumen and concrete roads, in Australia and around the world, that have corrugations. They’re not as pronounced as those that form on unsealed roads, but they’re there – particularly where trucks are climbing and descending grades.
Concrete road corrugations
The effect on car and 4WD occupants of these sealed road corrugations isn’t usually very noticeable, but if you’re in a heavy vehicle, or one with stiff suspension, you can feel these undulations through the seat of your pants.
Also, anyone in the rail transport business knows that corrugations on steel railway lines are a huge problem for fast-rail operators.
Railway line corrugations – ResearchGate
Steel railway lines and sealed roads don’t have loose surface particles, yet their surfaces can develop corrugations. Interestingly, the patterns that form on these hard surfaces have more ‘rippling’ on the inside radius of corners than on the outside – just like dirt road corrugations.
Rail line corrugation – typically 40-60mm in wavelength – has been around since James Watt, but has received a great deal more research since the very-fast-train era arrived. Uneven rail lines aren’t such a problem for slower trains, but high-speed trains are badly affected by uneven rails. Severe vibration and mechanical damage are common risks and that’s why there’s a great deal of research being done into preventing the formation of corrugations.
The current remedy for rail corrugation is regular grinding of the rails and that’s a wasteful, expensive and time-consuming operation. Even worse, the grinding wheel motion imparts its own pre-corrugation pattern into the rail surface!
But wait: there’s more. Rail lines develop undulations but so do power wires, in the case of electric trains that have overhead power supply. The motion of rooftop pantographs along the wires eventually causes corrugations to form on the power supply wires! When these reach a critical point the roughness causes arcing and the wires have to be replaced.
Corrugated rail problems are contributing factors as to why super-fast trains, like the Shanghai airport train that regularly hits 430km/h, use electromagnetic elevation (MAGLEV), rather than wheels.
You may have heard the aeronautical term, ‘cobblestone turbulence’ that describes the vibration in an aircraft that makes passengers feel like they’re travelling over a cobblestone surface – a lot like corrugations. What’s causing that is a difference in speed and direction of layered air masses.
So, it’s obvious that corrugations are more widespread than most people realise and occur in widely different environments. But is there a common factor?
It seems that corrugations occur where one mass is moving in close contact over another: ripples on a sandy shore or river bed are formed by water flow; corrugations on roads and rails form when wheels run over the surface; and aircraft turbulence is caused by conflicting air mass movements.
All around the world there are scientists busy in these different environments, trying to eradicate corrugations, so we’ll keep on top of their research.