Labour costs. TBMs are amazing but they are slow and require a whole lot of infrastructure. It's not just a case of sticking them in the ground, turning them on

Labour costs. TBMs are amazing but they are slow and require a whole lot of infrastructure. It's not just a case of sticking them in the ground, turning them on and waiting for a nice tunnel to materialize. For instance, what do you with the excavated dirt? To give you an indication of the sheer cost here, London's crossrail project runs at approximately £4m/day - https://en.wikipedia.org/wiki/Crossrail https://en.wikipedia.org/wiki/Crossrail