World Tunnelling > Global News > Raiseboring to rescue trapped Chilean miners

Global News

Things seem to be slowly moving at the San Jose gold and copper mine in Copiapó, Chile, following the collapse of a decline and vent shaft and the entrapment of 33 miners in a refuge bay 700m underground. It is as yet unclear what caused the collapse, but what is certain is that rescuing the men will take months. It was alleged yesterday that an emergency escape ladder that might have allowed the men to escape through a vent shaft was not installed.

Two boreholes created into the workings have allowed food, water and medicines to be sent down. But the arrival on site of a raisebore drilling machine mobilised from Codelco’s Andina mine will hopefully create a hole large enough to access the refuge bay.

Dean Brox, senior project manager at Hatch Mott MacDonald (Vancouver) has worked on several tunnelling projects in South American mines. He told World Tunnelling: “The size of the collapse in the ramp is not yet clear, but I have enquired as to whether it would also be safe to attempt a small adit through the ramp collapse as has been successful for civil tunnels when very bad ground is encountered, typically at major faults.”

He added: “The mind-set in mining is very different than for civil tunnelling and therefore civil methods are usually met with scepticism. But things are changing, which is why we are slowly becoming more involved in tunnels for mining projects and even introducing TBMs to the industry.”

Commenting on the suitability of raiseboring for the rescue, Mr Brox said: “The raisebore drilling attempt is appropriate and the method is highly successful for air and ore shafts in mining as well as hydro, but is no guarantee since they have to get through some bad ground. They must then ream out to 660mm, so keeping the hole open and stable may be the challenge, however unsupported vertical openings are more stable than unsupported tunnels. With this small size they will not be able to support the hole as they will need the clearance for access and egress.”

Raisebore drilling tends to be slow (6-10m/day) due to the large pilot bit size and the careful control needed. Reaming is even slower at half the drilling rate, so for 700m it will take at least three months. But, warns Mr Brox: “It also depends on the rock conditions: there is a risk that the drilling can get jammed or deflected off-alignment if very bad conditions are hit.”

Yet with air, water, food and medicines, the outlook for the trapped miners does not look too bleak.