[rdcbn]

A real curiosity.

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Probably more like a huge underground cavern or fissure

Not much else can stop that machine.

[freeagle]

So, maybe they need to bring in the bridge builders to cross the cavern?

[fso301]

Probably more like a huge underground cavern or fissure

Good point. An underground cavern might be fatal to the entire bore plan. I talked to a well driller once who said he lost an expensive bit when he drilled down into a cavern, or void of some sort and lost the bit.