On 7 May 2005 14:05:19 -0700, "lonelytraveller"
wrote:

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.

What are the chances of the floor of any cavern (even if it existed)
being at the exact level that the tunnel needed to go, or no lower
that some sort of bridging would be required? What protection would
there be for the tunnel segments if the roof of the cavern collapsed?
Bear in mind in the latter case that the ground clearance would be
apprecaitively less than that for a tunnel through solid grond, makign
it more vulnerable to bomb penetration.
--
Nick Cooper

[Carefully remove the detonators from my e-mail address to reply!]

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