How long does it take to dig one mile of subway tunnel by today's construction methods? What type?

Question

of machine (s) do they use? Is there a machine that will automatically lay track much faster than the old method of men with sledgehammers?

Answer 1

A tunnel boring machine can dig from 100 to 300 feet a day, depending on the material to be dug through. I saw that on the History Channel. But these machines are way too expensive for just a mile long tunnel. In a large city, it's common to dig the tunnel from the surface down, and recover the tunnel from the top again. This is necessary due to all the electrical, water, and sewer lines that will have to be rerouted. How long that takes can only be determined by the project planners.

Answer 2

30---50 days

Answer 3

What are they drilling trough? Hard Granite? Soft mud? Limestone? Shale?

It all depends!