Monday, May 08, 2006

Penetrating Cone Fracture explosives saves Australian miners

It was great to see the pictures of those Tasmainian miners walk out of the mine. The diagram comes from the BBC and shows how the rescue team bored a hole underneath the space the miners were in.

According to some reports the rock was so hard it couldn't be drilled. So, instead, the rescuers used a technique called PCF or pentrating cone fracture. It's a lot like a highly controlled, highly directional explosion.

I did a little research on PCF and this is what I found:

The Pentrating Cone Fracture technique uses a cartridge that consists of a hollow plastic tube that holds propellant. It is initially open at one end allowing the tube to be filled with propellant. The open end is then closed with a small cap. The other end of the tube is machined into a wedge to lock into the stemming and seal the hole when the cartridge is initiated.

When ignited, the PCF charge fractures rock or concrete by the introduction of a pulse of high pressure gas at the base of a drill-hole. The generated gas penetrates into small microfractures and fissures in the rock. These microfractures and fissures are forced to expand and propagate into tensile cracks causing the rock to fail.

A cartridge filled with a specially formulated propellant produces gas by deflagrating when the propellant is ignited. Because the gas is confined down the hole in a very small volume, very high gas pressure is generated when the propellant is ignited.

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