"David Spiro" wrote in message
...
"Tom Anderson" wrote in message
h.li...
I don't know that this was easier to
achieve due to the cut-and-cover method, or simply was a brilliant idea at
the time.

It's most definitely a better way of doing things, but prohibitively
expensive when drilling tunnels. With cut-and-cover, you just make your
trench a bit wider. With deep-level tunnels, you have to dig twice as many
tunnels.