I'm sure science exists to prove me wrong, but I get nervous when I think of how much solid air exists when you start putting tunnels underneath populous cities

I'm sure science exists to prove me wrong, but I get nervous when I think of how much solid air exists when you start putting tunnels underneath populous cities. An earth quake or a flood would destroy that infrastructure, and the decade or so it would take to excavate and build these things would probably sour the population to the idea.