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Does rain cause Tarmac / asphalt pot holes? If so, how?

After a period of rain in my city there are plenty of fresh new pot holes in the Tarmac / asphalt surfaces. The immediate cause is obviously axle overloading, due to appalling regulations, but these holes are fresh from a fourtnights heavy rain.

I can comprehend erosion in dirt or gravel roads as I know these substances are penetrable by water. But my impression is that Tarmac is impenetrable to water.

What process am I missing?

hazzey
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Samuel Russell
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1 Answers1

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old tarmac has cracks in it which can admit water under the material, softening the earth underneath. when a vehicle rolls over the cracked material, it yields because the softened earth fails to support it. in yielding, the cracks open up progressively and the tarmac develops a bowl-shape which collects water, which then drains through the cracks, softening still more earth, etc. etc. and in no time you have a pothole.

niels nielsen
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