How does a tunnel boring machine go underground and dig a hole?
When using this machine inside a city, a vertical hole called a “shaft” is first made. Then, a tunnel is dug laterally from that point. We call this the “departure shaft.”
Another shaft, an arrival shaft, is made at the arrival point to connect these two shafts using a tunnel.
Since a tunnel boring machine is extremely heavy, it is disassembled at the factory where it is carried to the departure shaft site to be re-assembled. This activity is often done from midnight to early morning. This is why most people have never seen this process.
When used at a mountain, a lateral hole like a tunnel for a road or a railway can be dug from the mountain slope. In general, after the tunnel has been dug and the machine has been disassembled, the “shield machine” portion of the tunnel boring machine will not be salvaged, along with the rest of the machinery It instead remains at the arrival shaft as a part of the tunnel wall.
Tunnel Boring Machine [THE GREAT PICTURE BOOK OF CONSTRUCTION EQUIPMENT]