And ya can't drill straight beyond 20m in any ground irrespective of using chrome couplers, 105mm rods or whatever and guess what? That implies a back to floor sublevel (or level) interval of about 15m at a production rate limited by ventilation capacity, which ties in nicely with a 15m limit on ladder slot or vent rises, beyind which the Mines Inspector (G'day, Cam!) gets shirty. There y'are, basic mining engineering, all done for ya's.
And ya can't drill straight beyond 20m in any ground...
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