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October 8, 2010 11:11 pm
The 33 miners trapped deep underground in a collapsed mine in northern Chile will have to help engineers in the delicate final phase of drilling and then blast the mouth of the tunnel with explosives to make sure their rescue capsule does not get stuck.
Engineers expect to have finished the 624 metre rescue tunnel by the early hours of Saturday, but the miners’ help will be needed to guide the drill as it “creeps down the last few metres”, says Greg Hall, whose company, Drillers Supply, is punching the hole through the rock to rescue the men.
Once the tunnel has been finished, the miners will widen the mouth of it using explosives which are already in the mine to give the specially designed rescue cage, dubbed “Phoenix” room to manoeuvre as the men are winched up one-by-one, according to an engineer from Codelco, the Chilean state mining company, who is involved in the drilling but asked not to be named.
Ministers said on Friday the rescue could begin as early as Tuesday, or up to 10 days more could be needed if engineers need to shore up the tunnel with a metal lining.
The miners, who can hear the drilling and are in contact with the engineers via a video link, will use a measured metal pipe to report back to the surface exactly how far away the drill is in the very final stages. “You want it to barely come through the top. You don’t want it to plunge down,” Mr Hall says.
The danger of going too fast is that the drill punches through into thin air and then gets stuck “and then you could lose the hole,” he added. Even though the tunnel his company is drilling – the so-called Plan B – is just one of three escape plans being drilled concurrently, it is the most advanced and the fastest, so any such setback could be disastrous.
The miners survived a cave-in on August 5 and took refuge in a shelter nearly half a mile inside the mine where they were discovered on August 22. They later had to move slightly deeper because of damp conditions, but the workshop where they will enter the Phoenix is an easy walk up a ramp from the shelter.
On the floor of the workshop from where they will be winched out, the miners will use rock that they have cleared as the drill approached to make a platform for easier access into the capsule. They will top the platform with planks of wood that have already been sent down to them via a communication hole, known as a “dove” through which they are also receiving food, medicines and entertainment. As well as collaborating in their rescue, they are also working out and doing breathing exercises to prevent problems during the rescue itself, which could take an hour per man.
The blasting with explosives will be “very small” and will just widen the entrance to the tunnel from the bottom, the Codelco engineer said.
Drilling was halted for several hours on Friday as engineers changed a hammer and drill. After too much use, they become worn and the hole they drill becomes smaller, another peril to be avoided to prevent the capsule from becoming jammed.
Engineers will decide once drilling is finished how much of the tunnel needs to be “cased”, or supported with a metal lining. Mr Hall said it was standard for the first 50 metres of any tunnel to need casing because the rock there tends to be very unstable.
By Friday afternoon, Plan B had just 37 metres left to drill but Mr Hall declined to say when it would break through to the workshop. “It’s bad luck in the drilling business (to talk about timing),” he smiled.
But he said: “We have to be careful, but we will get down there. We won’t give up till we get down there.”
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