Two miles of mountain does not "weigh down on you". As I said earlier, the alps are known to have very good rock. What this means is that it is, essentially,

Two miles of mountain does not "weigh down on you". As I said earlier, the alps are known to have very good rock. What this means is that it is, essentially, self supporting. You are not designing for two miles of overburden pressure, you are designing for maybe a couple diameter's worth of overburden. If you read my comment history you'll realize that I work in the tunneling industry. I have designed, inspected, or helped construct large diameter hard rock tunnels, small diameter soil tunnels, and everything in between.