They recently resurfaced the street in front of my house in Chicago. The first step was to grade away the existing layer of bitumen, to level the ground ready for a fresh layer. To my surprise (and I'm sure to the surprise of the engineers — the project was suspended for a couple of weeks), the old bitumen layer was hiding two sinkholes, one easily large enough to swallow a car. It was shocking to think we'd driven over that hole hundreds of times, and the only thing keeping us from falling in was a thin layer of bitumen.
As the video below explains, such sinkholes are usually caused by water erosion — in our case, probably by a broken water main. Check out the demo at the 4:00 mark to see how this can happen.
That's all for this week. Enjoy your weekend, and we'll be back with more on the blog on Monday.
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