<!--:es-->Hard rock slows Chile mine rescue<!--:-->

Hard rock slows Chile mine rescue

COPIAPO, Chile – The crew drilling the most promising of the three shafts attempting to reach 33 miners trapped deep underground has slowed its pace after hitting hard rock, officials at the mine said Tuesday.
As of Tuesday, the T-130 drill, part of an effort dubbed «Plan B,» has burrowed 466 meters (1,530 feet) of the 630 meters (2,067 feet) it has to drill to reach the miners.
The drill bit hit hard rock, however, and between Monday and Tuesday «only advanced two meters,» said Andre Sougarret, the engineer in charge of rescue operations.
The hard rock wore out the main drill bit, and the rescue crew had to halt operations overnight Tuesday to Wednesday to change parts, Sougarret said.
To advance more rapidly, the rescuers decided to narrow the bore hole by two inches, Sougarret said.
«There is excessive wear in the drill head, so we have decided to decrease the size of the (bore hole) diameter to 26 inches,» or 66 centimeters, Sougarret said.
Even though the shaft will now be narrower, Sougarret said there was still enough room to use a custom-built cage built to extract the miners, who have been trapped underground for two months.
The cage has an outer diameter of 23 inches (58 centimeters), Sougarret said.
Once the drill reaches the miners, engineers will have to decide if they need to line the shaft to strengthen the walls, a procedure that would add a week to the rescue plans.
The T-130 drill owners claim they can reach the trapped miners by the weekend, but Sougarret refused to set a date.
The other two drills involved in parallel rescue operations, the Strata-950 of «Plan A» and the huge RIG-421 oil drilling platform of «Plan C», were still far behind in boring a tunnel wide enough to pull out the miners.
The RIG-421 has reached a depth of 265 meters (869 feet). Engineers on Sunday decided to decrease the bore hole diameter from 28 inches to 14.5 inches, Sougarret said.
The «Plan A» bore hole had stopped at a depth of 587 meters(1,926 feet), and engineers expected to renew drilling on Wednesday. Though deeper than the «Plan B» bore hole, it must go to a greater depth of 702 meters (2,303 feet), and then be widened to be used in a rescue.

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