https://minewiki.engineering.queensu.ca/mediawiki/index.php/...
Honestly i would have thought it to be more expensive.
At higher depths the ground pressure is enormous and you need a lot of bracing.
Then there is water management, air, transportation of the dug out material...
When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.
https://minewiki.engineering.queensu.ca/mediawiki/index.php/...
Honestly i would have thought it to be more expensive.
At higher depths the ground pressure is enormous and you need a lot of bracing.
Then there is water management, air, transportation of the dug out material...
When there is rock you usually need blasting or gargantuan drills which i am not sure even exists in the required diameter.