Quote:
Originally Posted by MalcolmTucker
Well, the less dirt you have above a tunnel, the more structural strength has to be gained from the tunnel materials itself, not from adapting the ground to use as structure. Plus there would be codes on crossing underneath rivers - wouldn't want the tunnel daylighted during a flood event.
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Err, so a tunnel with no soil above it needs to be structurally stronger than one with soil above it....? The New Austrian Method acknowledges and exploits the inherent strength of soils to reduce the structural size of tunnels, but that does not necessarily mean it can be made less structurally strong as you go deeper (reducing the liner size), to a comparative shallower tunnel. Unfortunately I forget most of my soils mechanics and tunneling stuff from Uni, but that much I retained.
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