The physics behind potholes – and how to solve the problem
As monsoon rainfall floods Indian cities, it is worth remembering that a road, made using stones, sand and asphalt, is also a delicate water filter.
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Have you noticed that potholes in roads only happen during the monsoon? Why not when the weather is dry?
Imagine the point of impact when a tyre goes over a roughness in the smooth asphalt surface and comes down with a thump on the area just beyond. The force disperses through the dry soil below in a conical form so that each horizontal layer of soil below is subject to a smaller and smaller force per unit are as you move downwards. Until you reach a stratum where the force exerted is too small to matter.
Now imagine the same soil in a wet state. The interstices between soil particles are filled with water, not air. Water is incompressible. With the impact of the tyre above, the force will be taken by both the soil particles and by the water. The water pressure below the tyre is thus immediately felt by the water particles below and all around the area of impact of the tyre. The water pushes equally in all directions, into the water adjacent to it and the water below it, but equally it exerts an upward force on the asphalt above. That is what causes the adjacent asphalt to break and...
