That is only a small part of a TBM machine, namely the cutter head.
The entire machine includes equipment for generating power, moving the cutter forward, laying tracks, evacuating excavated material, and installing concrete tunnel support sections as digging progresses.
The TBMs actually used for digging the main channel tunnel are still underground, AFAIK. As the tunnel is lined with concrete behind the machine as it digs, the tunnel is too small to allow the machine to back out after digging. At the conclusion of digging, the machines were steered off to the side of the main tunnel, and abandoned in place.
