How Bridge Supports are Created in Water

How do engineers build the concrete supports for bridges over water?

They use a giant waterproof box called a cofferdam to keep the water out. Once it’s dry inside, they pour concrete and build the support from the riverbed up!

But that’s just one of the clever techniques engineers use.

If the water is too deep or the riverbed is too mushy, they go for drilled shafts or driven piles. Drilled shafts are like super-deep holes bored into the ground with giant rigs, then filled with reinforced concrete. Driven piles are long steel or concrete columns that get hammered deep into place — think of them like the stilts under a beach house, only underwater.

Once they’ve got a dry space (or a stable hole), the next step is to reinforce it. Huge steel rebar cages are lowered into place to give the concrete backbone-like strength. Then comes the concrete — and sometimes it’s poured underwater using a special method called tremie concrete. It’s sent down through a long pipe so it doesn’t mix with water and wash away.

After the concrete is poured, it needs time to cure — like letting a cake cool before adding the frosting. Once it’s solid, crews can build the rest of the bridge from floating barges or platforms perched on the supports.

Imagine building the legs of a table… while standing in a swimming pool. That’s what engineers solve every time they build a bridge over water.