Efforts to rescue the 33 trapped Chilean miners are being hampered by problems with the down the hole hammer, which is widening the borehole that will be used to reach them.
The connection between the hammer and the Schramm T-130 rig has broken several times, forcing engineers on site to check the integrity of the drill bit every 40m to 50m.
The hammer is widening the borehole from 300mm to 700mm to allow a rescue capsule to be lowered down the shaft to take the miners to the surface.
The steel rescue capsule arrived on site this week.
State-owned mining company Codelco is charged with carrying out the rescue operation. The firm’s general manager Fidel Báez said the angle of the bore drilling may be putting undue pressure on the connection.
“Maybe the angle is creating some difficulties. The connection is working more than [it would do during] normal drilling,” said Báez.
Báez said that the delays were unexpected but did not see the completion date of late October to early November being put back.
“Maybe the angle is creating some difficulties. We need to make sure we are accurate”
Codelco is drilling two additional boreholes so rescuers do not have to start from the beginning if problems with the main bore worsen.
Work on the third and final bore began this week with a 45m tall RIG 421 drill rig, normally used in geothermal exploration. A Strata 950 rig is being used on the second bore.
The borehole being created by the RIG 421 should be the fastest as it will not have to be widened.
But Báez said that initial progress has been slow using the third drill.
“The first 150m has seen very slow penetration. We need to make sure we are accurate.
We need to hit the correct angle so we arrive above the chamber [where the miners are stranded],” said Báez.
Báez predicted the RIG 421 will reach the miners in late October, around the time the first bore is due for completion.
Rescue capsule “still at concept stage”
Báez also admitted that he had “no exact method” of how the rescue capsule will evacuate the miners.
“It is just a concept. We will be working on a full protocol over the next month,” he said.
The capsule’s steel cage, which is just 1.9m tall and has an internal diameter of just 500mm can accommodate one miner at a time. Cage passengers will be fed compressed air from a tank beneath the cage. The air supply will last for 90 minutes, and the journey to the surface is expected to take 30 minutes.
Codelco is currently designing the winch and pulley system to bring the capsule to the surface. Báez said this would operate in a similar way to typical shaft sinking.
The 33 miners have been trapped 700m underground since 5 August when the main access tunnel collapsed at the San Jose mine, 725km north of Santiago.