How do they make sure tunnels are going exactly the right way?

Question

For example, when they’re digging the Euro tunnel how do they know they’re going gmthe right way and at the right depth etc.?

In: Engineering

Answer 1

I cant answer OP’s question but just got done watching a doc on how El Chapo escaped from prison the second time and holy shit, those guys dug a tunnel starting a mile away from the prison and popped up right inside the shower stall in his cell.

Call it what you will but that was amazing to me.