"polygonum" wrote in message
news
On Mon, 02 Jan 2012 09:17:12 -0000, John Williamson
wrote:

The Natural Philosopher wrote:
polygonum wrote:
On Sun, 01 Jan 2012 21:00:46 -0000, The Natural Philosopher
wrote:

polygonum wrote:
On Sun, 01 Jan 2012 18:30:22 -0000, dennis@home
wrote:


Its cheaper to bore one tunnel these days.

How much would it cost to bore, says, one mile of dual tunnel
capable of carrying two tracks, and how much for one tunnel large
enough for both tracks? Make any assumption you like about the
specification of the trains - e.g. Circle line standard.

essentially about 50% more material at a wet finger guess has to be
removed if the tunnel is circular.

I guessed around twice as much using simplistic pi r squared.

yerss but the bigger tunnel doesn't have to be 1.4 the diameter..its
an interesting thing really..I don't know how the actual tunnel 'fits'
the trains.

Very tightly:-

http://en.wikipedia.org/wiki/File:Wh...The_Tube. jpg

Certainly the clearance between the trains and the inner tunnel wall is
incredibly small. But when tunnelling it is surely necessary to consider
the outer wall? What does that add? Maybe a metre or two to diameter?

Maybe a foot.