(just a guess) even if you are only using it for a small fraction of its lifetime, you are amortizing the cost of a large piece of capital equipment, so the upf

(just a guess) even if you are only using it for a small fraction of its lifetime, you are amortizing the cost of a large piece of capital equipment, so the upfront cost must take this into account. Blasting has a smaller investment in capital equipment (even if amortized similarly) There is also the setup- carting in the pieces of the TBM and getting them into place, etc.