How do people in New Orleans build the foundations of buildings if they are so far below sea level?

Question

If graves have to be above ground because of the water level, how do they get the foundations so deep?

Answer 1

several ways.

if the building is large enough then it will have to bear on bedrock, which is about 70-80' down in new orleans, which means a bunch of 70-80' tall piles

that is why projects in areas with that soil condition have that loud hammering sound for months, that is the pile driver... clang clang clang clang...

or

friction piles  (they don't bear on rock, the friction against the soil around them holds the building up)

floating mat foundation

large projects would require shore walls and a sump to keep the water out during underground construction.

Answer 2

Sorry Robert W but you need to check the geology: Bedrock is thousands of feet down at New Orleans.

Most buildings in New Orleans are constructed using pilings. The ground is not all the same density so some areas require longer or more pilings than others for a house or other standard building. There were also many single-story homes built after WWII using the slab-on-grade technique (no pilings, just a slab)

The skyscraper-type buildings in the city are constructed using a technique called "floating pilings". The building "floats" on top of a pillar of pilings driven far into the ground.

Almost no buildings in New Orleans have basements due to the high water table.