Re:Under Seattle, a Big Object Blocks Bertha. What Is It?
by Retric on Friday December 20, 2013 @09:41AM
(#6941563)
You don't need to worry about the drilling surface as the TBM's building a concrete tunnel inside of it's self. However, distance from the drill head and friction means your not dealing with full pressure back there.
It's a little hard to picture so jump to 5m on this video. http://www.youtube.com/watch?v=Dk-8Q42NCSQ