If you’ve ever put up a shelf, you already know how drilling is supposed to work. You push the bit into the wall, and the dust spills back out toward you.<\/p>\n
Raise boring flips that around. A rig on an upper level of a mine drills a skinny pilot hole down to a tunnel below. Then a crew bolts a much bigger cutting head onto the bottom of the drill string, and the rig drags it back up, spinning, while the broken rock falls away underneath.<\/p>\n
Mines mostly use the trick for air shafts and ore passes. At Jansen, BHP’s potash mine in Saskatchewan, a contractor used it to make a room.<\/p>\n
In June, Thyssen Mining said its raise boring crew had pulled two of these holes side by side between two of the mine’s underground levels, close enough to overlap into one long chamber, as International Mining reported<\/a> at the time. The finished space is 26 feet wide, 49 feet long and 112 feet tall, and it’s going to be an underground storage bin for raw ore.<\/p>\n That’s about as tall as a 10-story building. Thyssen puts the rock that came out of it at 6,146 tons.<\/p>\n Blasting is the usual way to make a room underground. It works, and it’s been working for well over a century. It’s also pretty slow. You drill a pattern of holes into the rock, load them with explosives, clear everyone out and set them off. Then you wait for the air to clear, haul out the rubble, secure the roof and start the whole loop again.<\/p>\n A raise borer skips most of that. No one has to stand in the hole while it’s being cut, because the rig sits on the level above and the rock simply drops to the level below, where a loader can scoop it up. The walls tend to come out smooth, too, so they often need less support afterward.<\/p>\n Thyssen says boring the bin this way saved 64 days compared with digging it out conventionally. Two months might not sound like a lot on a project this size. But Jansen’s first production date has already been pushed back once, so I’d imagine no one on site complained.<\/p>\n The machine that did the pulling is a Robbins 123RVF, one of the biggest raise drills in the Robbins line, which belongs to Epiroc these days. The Robbins spec sheet puts the 123RVF’s derrick (more or less the drill itself) at about 37 tons and roughly 19 feet tall with its frame fully extended.<\/p>\n The VF in its name is short for variable frequency. Basically, that’s an electric drive that lets the operator change how fast the drill string spins and put a cap on how hard it twists.<\/p>\n Do the math, and that 37-ton drill cut loose 6,146 tons of rock, more than 150 times its own weight. That spec sheet also lists the 123 series for holes from 8 to 20 feet across, and Jansen’s two came out 26 feet wide.<\/p>\n So what’s the trick?<\/p>\n From the looks of things, it’s mostly the reamer, the big cutting head bolted to the drill string. Jansen’s was designed and built by Epiroc. I couldn’t find a weight for it anywhere, which is a shame, since that’s the piece of hardware I’d most like to see on a scale. Frankly, using two overlapping circles is a pretty clever way to get a long room out of a machine that only makes round holes.<\/p>\n Figures: Thyssen Mining, Robbins 91\/123 spec sheet.<\/p>\n Thyssen also says it believes the dig “matches the world record” when it comes to the widest hole ever pulled by raise boring. As far as I can tell, the record it’s talking about belongs to an access shaft at the No. 7 coal mine near Brookwood, Alabama.<\/p>\n More than a decade ago, a contractor called Raisebor pulled a 26-foot-wide raise there that runs 1,440 feet deep. It used a Robbins 123RH C, from the same family as the Jansen drill, and a custom reamer nicknamed the Moose. Epiroc’s own write-up<\/a> calls the job “possibly the biggest raise ever bored.” The Moose’s cutters weighed more than 400 pounds apiece, according to Coal Age.<\/p>\n Jansen’s holes tie Alabama’s on width, but they’re 112 feet tall, and Alabama’s raise runs 1,440 feet deep. I’d say that’s fair enough, since no one needs an ore bin that deep. I also couldn’t find any official referee for raise boring records, so the world record part is Thyssen’s own call.<\/p>\n BHP’s latest technical report on Jansen<\/a>, which it filed with its annual report, lists raw ore storage bins among the facilities in the area around the mine’s two shafts. They’re on that list next to the skip loading stations and a network of conveyors.<\/p>\n If you’re wondering what a skip is, it’s a giant steel bucket that rides up and down the shaft. Jansen’s production shaft is due to get two of them, each carrying about 83 tons of ore, once its permanent hoisting gear goes in.<\/p>\n A bin like this is essentially a buffer. Conveyors can keep dumping ore in while the hoist is busy, and the hoist can keep running when the conveyors stop, so neither has to sit around waiting on the other. It’s pretty much the same idea as the tank on your water heater.<\/p>\n I couldn’t find how much ore this particular bin is meant to hold, or exactly when it’ll take its first load.<\/p>\n Potash is the stuff that puts the potassium in fertilizer, in case you’ve never had a reason to look it up. Jansen is BHP’s first potash mine, and we’ve already covered how BHP froze 2,625 feet of waterlogged sand<\/a> to get its two shafts down. It isn’t the only Canadian drilling job we’ve written about lately, either. Two drill bits recently met nose to nose under a Canadian river<\/a>.<\/p>\n Jansen’s costs have been a pretty sore spot. BHP now puts Stage 1 at $8.4 billion, up from the $5.7 billion it originally approved. It also booked a $2.3 billion impairment on the project in its latest financial year, which is accountant-speak for marking down what the mine is worth on its books.<\/p>\n Once Stage 1 is fully ramped up, BHP expects it to turn out about 4.6 million tons of potash a year. In its full-year results on August 18<\/a>, the company said Stage 1 was 84% complete at the end of June, and it’s still targeting first production in mid-2027.<\/p>\n","protected":false},"excerpt":{"rendered":" If you’ve ever put up a shelf, you already know how drilling is supposed to work. You push the bit … <\/p>\nSo why not just blast it?<\/h2>\n
The drill is rated for holes up to 20 feet<\/h2>\n
Is it really a world record?<\/h2>\n
A mine this size needs somewhere to park its ore<\/h2>\n
Jansen’s first potash is still due next year<\/h2>\n