[freebeard]

Originally Posted by rmay635703

Remember Musk doesn’t have a corner on boring the government core of engineering can do it also
[snip]
Next issue is that a small car sized tunnel likely can’t supply enough water to overcome evaporative and “hydraulic conductivity “ and the cost to bore larger raises the costs significantly, you also have additional costs to reinforce/line the tunnel to be filled with water (dry tunnel is cheaper)

Too bad TBC can't access nuclear propulsion.

A real-world, mobile subterrene must work thermally, using very high temperature and immense pressure to melt and push through rock. The front of the machine is equipped with a stationary drill tip which is kept at 1,300–1,700 °F (700–930 °C). The molten rock is pushed around the edges as the vehicle is forced forward, and cools to a glass-like lining of the tunnel. Massive amounts of energy are required to heat the drill head, supplied via nuclear power or electricity. Patents issued in the 1970s[1] indicate that U.S. scientists had planned to use nuclear power to liquefy lithium metal and circulate it to the front of the machine (drill). An onboard nuclear reactor can permit a truly independent subterrene, but cooling the reactor is a difficult problem.[2] The Soviet Union is purported to have built such a "battle mole", which operated until its onboard reactor failed.[3]

Online information[clarification needed] presents research that was funded by the United States Government for the Los Alamos Scientific Laboratories University of California, Los Alamos, New Mexico for a project Camelot under the heading Systems and Cost Analysis for a Nuclear Subterrene Tunneling Machine. A patent was subsequently issued under number 3,693,731 on September 26, 1972.[4]

en.wikipedia.org/wiki/Subterrene

They produce a dense vitrified tunnel wall.