I had a chance to ride in the tunnel system at the Las Vegas Convention Center built by Elon Musk’s Boring Company. If was a fun experience, although the tunnels were significantly tighter than I expected. The driver told us that a “test” they need to do as a part of training is drive through one backwards which did not sound fun to me.
The company recently held a tunneling competition with 400 applicants reduced to 12 finalists to compete in building an actual tunnel in the Nevada desert with their machines. The winners were a team called Swissloop Tunneling who used in situ 3D printing to reinforce their tunnel as it was being built. Pretty cool to see another construction use of 3D printing!