How do they make pillars long enough to reach the sea floor for Sea Bridges?

Question

And doesn’t the water pressure make everything more difficult to work with?

In: 540

Answer 1

Look up what a “cofferdam” is. They basically put a watertight fence around the area where the pillar will go, then drain all the water out. Now you have a dry area in the middle of the water where you can build a pillar as you would on land. Once the pillar is built, you pump water back in and remove the cofferdam.