What lies beneath

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Q. We’re hoping you can tell us what to do about our driveway. It’s been sinking for a few years now, and we had it patched two summers in a row. The asphalt company told us it’s time to replace it, that the problems are from underground streams or air pockets. I remember reading about this in one of your columns about two years ago, right after the big storm. We weren’t flooded, so I suspect that the problem is something else. What do you suggest?

A. It doesn’t take a storm to have a sinking driveway. Like anything exposed to nature, there are many reasons for failure, some preventable because they’re predictable, some predictable but not preventable. For example, the weather wreaks havoc on exposed materials, from freeze and thaw, day and night temperatures, a cool rain on a hot day, anything that stretches your driveway like a big bar of taffy.

I remember driving on a main road when traffic suddenly stopped. Emergency vehicles began to pass. I suspected an accident, which it was. People seemed shocked that on this very hot day, a car had a head-on collision with the road, which had buckled, jutting the roadway upward with sudden and surprising force. I wasn’t amazed, just curious about the suddenness of the movement. Sometimes materials expand slowly, and sometimes they shift like an earthquake, without warning.

Compound the temperature with changing support below the pavement due to moving earth, and you get sinking. It can be from an underground stream, since water is everywhere just below the surface, at varying depths. The water flows more with heavy rain, less in a drought. Sinkholes form as flowing water moves earth from place to place, or when there’s so little water that the normally water-saturated material compacts from being so dry that it sinks under its own weight, filling air pockets that no longer have water in them. Sounds like an earth science class, doesn’t it?

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