If he wants to get into the tunnelling business and start bidding on these "big dig" projects in various cities, I think he'll find some success. His engineering aptitude, his ability to think around problems, that's gotten him to where he is today.
If he retreats from this and builds some kind of pneumatic tube system to transport goods, people, or whatever, he still might have a chance of a win. Those systems have been proposed, and in some cases actually built, and in many cases they've been great ideas.
If he stubbornly insists on pursuing this batshit insane system of tubes he will fail, and he'll fail hard. There is not enough concrete in the world to make that many tunnels.
Maybe he can. The construction industry has explored a lot of options, but let me tell you something: If there's one group of people that are necessarily conservative about these things it's civil engineers.
A rocket can go to the moon and come back safely, that takes an abundance of caution and significant attention to detail, but it's a fixed-length trip. Civil infrastructure has to exist for decades, or in the case of many American undertakings, well over a century. That requires extreme caution.
If you invented a concrete alternative today it'd take at least twenty years for it to be considered a viable alternative to concrete because long-term studies of the mechanical characteristics of it under a wide variety of conditions will have to be taken out.
Concrete is an extremely complicated material, I know people that have gotten a Ph.D. in aspects of it, and it's very well understood. This hypothetical alternative you're talking about has a lot to measure up to.
If he retreats from this and builds some kind of pneumatic tube system to transport goods, people, or whatever, he still might have a chance of a win. Those systems have been proposed, and in some cases actually built, and in many cases they've been great ideas.
If he stubbornly insists on pursuing this batshit insane system of tubes he will fail, and he'll fail hard. There is not enough concrete in the world to make that many tunnels.