On: Tunnel Boring Machines (2018)

[koheripbal]

This is only if you build subway tunnels which are very shallow.

Deeper tunnels for longer distance transport do not have any of these limitation.

[bluGill → koheripbal]

Deeper tunnels cut and cover get expensive fast, bored tunnels are about the same cost at any depth.

[KaiserPro → koheripbal]

this is purely for cut and cover.

As soon as you don't need to break the surface, the cost drops significantly, and the speed of build, planning and after care increase dramatically.