'Unconventional' drilling could free trapped Chilean miners
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An ‘unconventional’ drilling method is expected to bore the escape hole for the 33 miners trapped in a San Jose copper mine in northern Chile, according to an industry expert.
Dr Andrew Wetherelt, a senior lecturer in mining engineering at the University of Exeter, said Chile’s state-owned Codelco mining company is planning on using a massive Strata 950 ‘raise boring’ drill to carve a hole 66cm wide to reach the miners trapped under solid rock 700m below the surface.
This hole will be drilled after the rescue team has completed drilling a smaller pilot hole.
In traditional raise boring operations, Wetherelt said mining companies use a drilling technique known as ‘up-reaming’ where machine cutters are fitted to the drill sticking out the bottom of the pilot hole. The massive cutters are raised up as they hack their way through thick rock.
Wetherelt said this is not possible to do in the case of the mine in Copiapo, Chile because the collapsed mine offers no access to the bottom.
Instead a technique known as ‘down boring’ will need to be deployed, he said, In this case, the operators will drill an oversized pilot hole and install a cutting head at the surface. The operators will guide the drill downward and rock clippings will flush down the pilot hole to the bottom where the trapped miners will likely be expected to sweep them away.
Wetherelt said this technique is less common than up-reaming, because there is a risk of plugging up the hole with rock clippings. The miners will play an essential role in making sure this doesn’t happen.
There is also the challenge of keeping the drill and its cutting head stable as it pushes its way through layers of abrasive rock. Wetherelt said rotating stabilising wheels clamped onto the drill will help ensure it does not deviate from its path. Otherwise the awesome piece of drilling machinery may just, as Wetherelt puts it, ‘bend like a hairpin’.
The 5 August collapse of the mine’s main access shaft happened about 400m below the surface. This was above where the miners were working at the time. The group took refuge in a gallery approximately 688m below in an area that stretches about 2km long, which should leave enough space for the likely restless men to walk around.
The mine, which runs under a mineral rich mountain in northern Chile’s Atacama Desert, incorporates a zigzagging main access ramp–large enough to drive a car down– and vertical shaft tunnels that are meant to be used for escape when the other means of egress has failed.
Without a 3D map of the mine, Wetherelt said it is tough to make certain judgments on how much safety was taken into consideration in its design. However, it is clear the catastrophic underground failure three weeks ago blocked off both means of escape for the miners.
Wetherelt said, ‘Clearly in this instance there is a problem that the catastrophic failure has also damaged the shaft,’ he said. ‘The failure has gone across the ramp so in doing that the ramp is out of condition but the fact is the shaft is also in close proximity to this failure.
‘We (the UK) have legislation that there should be two means of egress and they shouldn’t be next door to one another in three dimensional geometric space.’
Wetherelt said he is unsure what legislation dictates about mine design in Chile, but if there are others like the one in Copiapo up and running ‘that’s clearly not good’.
Meanwhile the trapped miners in Chile have been receiving food, water and oxygen supplies. Today it was announced the miners have been told for the first time the rescue operation may take until Christmas.
Wetherelt said there is a chance it might not take that long. ‘They’re not being pessimistic but I don’t think they want to get anybody’s hopes up to say they can do it in a week.’
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Readers' comments (13)
Anonymous | 27 Aug 2010 3:43 pm
I the 1950s there was a Kirk Douglas film entitled, as I remember, Ace in the Hole about a man trapped underground. I do hope the Chilean authorities will not make the same mistakes.
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Anonymous | 27 Aug 2010 4:13 pm
TV reports say the miners are in a volume 'about same a 1 bed flat.' Estimate = 120 cubic Meters?
If "up-reaming" is used the miners will need to fit around 240 cubic meters of rock spoil + themselves into 120 cubic meters!
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Michael Dunsmore | 27 Aug 2010 6:49 pm
The article said
"The group took refuge in a gallery approximately 688m below in an area that stretches about 2km long, which should leave enough space for the likely restless men to walk around."
The 2km will also leave plenty of space for the 240 cubic metres of rock spoil.
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Tony Clancy | 27 Aug 2010 8:26 pm
It is absolutely evident in these mining disasters that only the minimum of forethought for the safety and alternative entrance and egress to mines everywhere in the world. Miners are expendible, billionnaire owners don't lose their lives, perhaps if they were likely to do so miners would be safer. There's no simple all solving answer but there are answers in the planning of mines and in the layout and underground access points to surface and to safety...but as I inferred, what's a few dozen dead miners when money is at stake?
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Tony Clancy | 27 Aug 2010 8:26 pm
It is absolutely evident in these mining disasters that only the minimum of forethought for the safety and alternative entrance and egress to mines everywhere in the world. Miners are expendible, billionnaire owners don't lose their lives, perhaps if they were likely to do so miners would be safer. There's no simple all solving answer but there are answers in the planning of mines and in the layout and underground access points to surface and to safety...but as I inferred, what's a few dozen dead miners when money is at stake?
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Andy Wilson | 27 Aug 2010 9:21 pm
"Ace in the Hole" is a Billy Wilder film produced in 1951 about a cynical journalist intent on trapping people down a mine.
See:http://en.wikipedia.org/wiki/Ace_in_the_Hole_%28film%29
The Chilean situation has nothing to do with this.
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Rick | 28 Aug 2010 1:52 am
Having worked in 2 gold mines I can vouch for some of the safety hazards and primitive working conditions. Kirkland Lake ,Ontario has the deepest gold mine in the world with the main shaft dropping 7,000 feet.My thoughts go with the miners who must endure.
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JG | 28 Aug 2010 7:01 am
"Without a 3D map of the mine" - in most countries, the Mine Surveyor was a respected and well trained member of the mining team. New and faster methods are now available for 3D surveying of such internal volume. They should be compulsory, in all mines world-wide. Safety is only one of their applications..
The reason a big hole takes longer to advance than a small one is, the cutting edge of the drill has a defined speed for the bit and material removed. Bigger hole, bigger circumference, slower advance for same cutting speed.
Laser rock cutting methods have been trialled, dependant on rock type, expensive and less available worldwide than friction/cutting.
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R. Choudhury | 28 Aug 2010 10:19 am
I am by no means a mining expert, but could they not simply send people down the original sloping mine shaft to create a passage through the fallen rock that is large enough for the miners to crawl through?
Even if the ramp is broken in parts, so that large excavators and digging equipment cannot be taken down, couldn't people be sent down the shaft to do the work manually with smaller equipment? Surely the rockfall is likely to be looser than the 700m of rock they are currently planning to dig through, and there would be much less rock to dig through, so this method would take significantly less time than the 3 months currently projected!
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kevin addiscott | 29 Aug 2010 12:42 pm
when the miners ,made thier way to the escape ladder and found it was missing ,so they made thier way to where they are now ,what about this hole where the ladder was could they not get them out this way
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