Another tunnel collapse has hit the headlines this week. This time it is in Prague on a highway tunnel being built on a ring road around the Czech Republic's capital. Local newspaper reports tell of a collapse crater on the surface of 20m wide x 30m long and of an excavator driver and his machine being buried under the fall, but rescued and released after a short hospital stay. Fortunately, there are no reports of serious injuries or fatalities or of structural damage to surface buildings or underground infrastructure in the area. The collapse is said to have occurred in the small hours of Tuesday 6th July at 1am, and on a section of tunnel designed and being constructed according to the NATM concept.
Ah well, maybe a few extra billion for the Niagara Tunnel isn't so bad... I find this article interesting, with the concept that engineering margins are so thin that a sleepy night shift can bring the tunnel down. I mean, really, who the hell works the night shift! Can you imagine some lower-ranked junior engineer down there? -- "Ah, excuse me, but I think that water is not a good thing...could you please stop and give up your bonus? Hello?"
When designing these things you should account for the night shift. That, of course, makes the cost go up,since it is a pessimistic assumption, and we all know these things are priced on all assumptions being extremely optimistic.