On Sun, 8 May 2005, Clive D. W. Feather wrote:

In article .com,
lonelytraveller writes

What I meant was, wasn't it possibly for them just to add the
prefabricated steel tunnel rings into an already existing cavern? It
would save a lot of effort.

Even if such a cavern existed (which I doubt), putting a line of steel
rings across it isn't easy - they'll all fall down! You need to build a
viaduct across it (as was done on line 7bis in Paris).

That sounds interesting. What sort of cavern was it? I have visions of a
tunnel emerging into some vast underground space deep beneath Paris -
probably lined with the bones of 19th-century hermits or something - and
crossing it on some impossibly slender bridge before plunging back into
the rock. Which would be cool.

Or are you suggesting that there's a natural tunnel-shaped cavern under
East London?

I got the impression 'cavern' meant some sort of manmade hole related to
the tube in some way. As in 'crossover cavern'.

tom

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