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

There are numerous techniques.

One common one that is often used in waters that are sufficiently shallow is cofferdams.

Basically they pick where they want to build and erect a temporary dam around the place and pump out the water creating a sort of island below the sea level for them to work on.