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Why Bridges Don't Sink

[Note that this article is a transcript of the video embedded above.] The essence of a bridge is not just that it goes over something, but that there’s clear space underneath for a river, railway, or road. Maybe this is already obvious to you, but bridges present a unique structural challenge. In

You would need either an enormous weight to take advantage of gravity or some other strong structure attached to the ground to react against and develop the pushing force required to drive it downward. They can’t easily go through hard geological layers, cobbles, or boulders; they can wander off path, since you can’t really see where you’re going, and they can cause the ground to heave because you’re not removing any soil while you force them into the subsurface. In ideal conditions, you can get a nice seal between the bottom of the casing and the soil, but even then, it’s pretty hard to keep water out of the hole, and luckily it doesn’t matter.

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