A Bit of an Engineering Problem

Pacific Standard looks at the expansion of the Bingham Canyon copper mine in Utah:

The tunnels are only the very beginning of the underground project at Bingham Canyon. According the plan, they will wind 2,000 feet beneath the ore body. Then, 300 miles of smaller tunnels will be bored across the rock, one above another, creating a dual-layered lattice. The layers will be connected by vertical funnel-shaped shafts. Finally, the ore above the upper lattice will be blasted, and the shattered ore will flow down the funnels to the lower lattice, from which it will be removed.
Secondary problems will have to be solved. The rock is saturated with groundwater; thousands of drainage holes must be drilled, and a massive pumping system installed, to keep the tunnels from flooding. Because so many miles of latticework must be constructed, Rio Tinto plans to use speedy tunnel-boring machines rather than traditional drill-and-blast techniques. But machines that meet its needs—that can operate at steep angles and turn in tight radii—don’t yet exist. They’ll have to be invented. Rio also plans to use robotic trucks and scoops to remove the ore. (“We’re going to drive them from the surface using PlayStation controls,” Gass said.) That system will have to be custom-built, too.
For Bingham, as for any mine shifting underground, the pay-off for all this preparation would be twofold. First, after the initial blast, the production of ore is self-sustaining. The ore body simply collapses under its own weight, and as one load of broken ore is trucked out, more flows in to replace it. It’s a safe, predictable process; essentially, gravity does the work of dynamite. Second, unlike in pit mining, no overburden—the ore-free junk rock—has to be shifted. Underground mines shift ore and nothing else.
The technique, known as block-caving, is not new, but the scale is. Copper mines are measured by the amount of ore they process. “Twenty years ago, a big underground mine would have been six, eight thousand tons a day,” Gass said. “We’re designing this to be over a hundred and fifty thousand tons a day”—as much as the pit now produces. After the first set of five block caves has been mined out, sometime decades from now, a second set below it may follow. A third, still deeper set is possible after that. Ultimately, more ore may be dug out from underground at Bingham than will be removed from the open pit in its entire existence.

Wow, that sounds like a lot of fun.  I really can't imagine the scale of that place.  Further up in the article it says that for every day's 150,000 tons of ore processed, they get 820 tons of copper and 149,000 tons of tailings.  What a fucking mess!  Earlier in the year, the mine had a landslide which closed the pit and will probably cut output in half.  If you like major engineering feats, read the whole thing.