The rescue effort to reach 33 trapped Chilean miners suffered a major setback this week when the drill bit being used to bore a rescue shaft snapped.
Drilling halted last Thursday when the Schramm T-130 drill bit – boring one of three planned shafts to reach the stranded miners – struck an iron support beam about 300munderground.
Rescuers have now retrieved the pieces of the shattered drill and are now redrilling the last 10m of the bore.
Chile’s mining minister Laurence Golborne insisted that the setback would not delay efforts to rescue the men, who have been trapped since 5 August.
Equipment failure was foreseen by rescuers.
State owned mining company Codelco is carrying out the drilling operation.
Collapse “not expected”
“We don’t expect any risk of collapse because of the quality of the rock. It is principally diorite and is 150MPa, and up to 250MPa in some areas,” said Codelco general manager of underground mining Fidel Báez.
Three rescue shafts are being bored to reach the miners. Two are currently under construction.
The stalled Schramm T-130, known as Plan B drill, is the higher velocity of the two rigs on site. Despite starting drilling five days after Plan A drill – a Strata 950 – Plan B had covered a greater distance and was averaging between 25m and 30m per day.
Both drills are boring 300mm to 330mm pilot holes above the area where the miners are trapped. The Plan A bore will be reamed to 700mm with a larger drill bit so a rescue capsule can be lowered down the shaft.
Plan B’s bore will be enlarged using “down the hole” hammer drilling.
Constant mapping with cameras within the hole will ensure the shaft is vertical.