The foundation pipes will be rammed into the ground, I don't think any coating will survive this procedure. Special (sea water resistant) steel would be too expensive, given the large quantities necessary.
Zinc coating is a bit different: The corrosion protection results from the coating of the entire surface. Within air the zinc forms a dense coating of zinc carbonate that protects the zinc from further corrosion.
Of course if the zinc layer is destroyed at some place the electrochemical process begins and its speed will depend on the area affected and the amount of humidity and ions present.
But even without holes in the coating the zinc layer degrades at free air, I believe it is roughly about 1µm/a.

Joerg.