When building a bridge over a large body of water, how do they get the pillars so deep into the water and how is the foundation secured?
In: Engineering
These days, there are a few techniques. But the most common is it drive steel pipes into the river or ocean bed, then use an auger – a big soil drill – and pumps to extract the soil from inside the pipe. Don’t worry about the water. They extract soil below the bottom of the pipe, too, so that there is a void underneath the base of the pipe. Then they drop steel reinforcing into the pipe, and fill the pipe with heavy concrete. The concrete is heavier than the water is, so it stays at the bottom and the water is pushed out of the top.
You then end up with a concrete pile – the steel rusts away, but it’s only there to help form the concrete pile – sitting on a concrete plug that is down beneath the river bed. The finished construction looks like an upside-down mushroom, deep down in the soil. Each one of those piles can support a lot of weight, and as there aren’t expensive to put in, they put down a lot. Then a headstock is cast on top of them, and the bridge (or other construction) built on the headstock.
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