People also tend to object to "move fast and break things" when they, and their very expensive buildings, are on top of said things and get broken as a result.
Point. Although I'd assume the majority of subway routes tend to be built under roads (also bad, but less terrible)?
Not sure what the geology of San Francisco / California tends to be like, but I believe most of the Manhattan skyscrapers are anchored down to the bedrock. Which I'd expect would require cutting and reinforcing vs just "drill on through".
People also tend to object to "move fast and break things" when they, and their very expensive buildings, are on top of said things and get broken as a result.
Point. Although I'd assume the majority of subway routes tend to be built under roads (also bad, but less terrible)?
Not sure what the geology of San Francisco / California tends to be like, but I believe most of the Manhattan skyscrapers are anchored down to the bedrock. Which I'd expect would require cutting and reinforcing vs just "drill on through".
Ultimately you want to put passengers in the tunnel, yes?
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)