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?

Question

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

Answer 1

You use something called a cofferdam or caisson. Basically you build a temporary barrier around the area where you want to build, which you then pump out all the water. Cofferdamns extend the existing shoreline while caissons are freestanding in the water. You then build the bridge pier up inside them. Once it’s above the water, and the concrete is cured enough, you can flood the dam and remove it.