In the last entry, you saw those cool, circular tunnels that will house Manhattan's new 7 Train extension, lined with pre-fab concrete sections. Above is a photo of a similar tunnel in Delhi. Question is, how did they dig and line these things?
They use what are called TBMs, or Tunnel Boring Machines. These massive machines are essentially moving factories that cut through the rock, excavate the waste out of the back, and install the concrete shielding, all while pushing itself along like an inchworm. You'll understand the process better after viewing the video at the bottom of this entry, but first, here's some examples of what TBMs look like from the front:
Size matters.
Lubrication matters.
I think this one has no motor and is powered by the really strong guys in the red and
orange shirts. (The guys in green and yellow shirts are there to yell encouragement.)
Japan has a bad-ass triple tunnel boring machine.
In a manner of speaking, it's three times as boring.