Comment by ethbro
9 years ago
From parent comment, I was guessing that the point of greatest risk would be during tunneling / initial bracing? Rather than final static bracing.
9 years ago
From parent comment, I was guessing that the point of greatest risk would be during tunneling / initial bracing? Rather than final static bracing.
I was thinking of the NATM failures: http://www.tunneltalk.com/images/laneCoveCollapse/Ref5-Heath...
(which were during construction, but happened in "finished" sections, I believe. NATM applies a single pass of shotcrete to the cut rock surface)