Dude, take my word for it, I spend 18 years as a carpenter/builder and another 18 years as a piping designer and structural designer. I have spent my life in the field and pouring over old drawings. I've been 1800 feet below the surface.
Quote:
Originally Posted by oberon_1
Only the first line in Brooklyn which dates back to 1850s was dug as an open trench and later covered. Many tunnels go under rivers and these had to be dug deep from day one. One way or another, the old undocumented infrastructure, does not tell today's picture. Even new projects take much longer than a century ago. The same goes with NASA. and with defense projects. It must be something in the air.
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These are typical cross sections, stacked and horz four track arrangements. MOST early subway were open trench excavations.
Keep in mind NYC isn't the center of the universe. London's tube is close to the surface, too.