You might want to take a look at how painful the undersea tunnel across the Bosphorus have been. Quite a well written article as well: https://www.newyorker.com/magazine/2015/08/31/the-big-dig

In short — when contract builders determine depths of tunnels based on earliest known human habitation, it’s often the case that they find humans got there earlier than thought. Then the proposed great solution to the traffic problems instead becomes an archeological dig site for the next decade.