My mine is looking to install a 600 mm open borehole to drop particles up to 150 mm through. It's a 320m shaft to drop ballast down to save time compared to using the drift.
When it gets blocked they typically take a water truck out and that works. They have used explosives to clear a blockage before but that was a decade ago.
Some of the seniors have rough rule of thumbs on the borehole diameter required to drop particles without causing a blockage but I'm unable to find any references. And it is based on experience and what they've always done. I'm unaware of any design work for this beyond "this should be large enough", but believe there should be more behind it than that.
Is there a formula available to determine the borehole diameter required to safety drop in the particles?