Rescue plans for 2010 Copiapó mining accident

The 2010 Copiapó mining accident began as a cave-in on 5 August 2010 at the San José copper-gold mine in the Atacama Desert near Copiapó, Chile. The accident left 33 men trapped 700 meters (2,300 ft) below ground who survived underground for a record 69 days.^[1][2] All 33 men were rescued and brought to the surface on 13 October 2010 over a period of almost 24 hours. After the last trapped miner was winched to the surface, the rescue workers still underground held up a sign before the camera stating "Misión cumplida Chile" (English: "Mission accomplished Chile") to the estimated more than 1 billion people watching the rescue on live television around the world.^[3]

The San José Mine is about 45 kilometers (28 mi) north of Copiapó, in northern Chile.^[4] The miners were trapped approximately 5 kilometers (3 mi) from the mine entrance. The mine had a history of instability that had led to previous accidents, including one death.^[5][6][7]

The retrieval of the first miner, Florencio Ávalos, began on Tuesday, 12 October at 23:55 CLDT, with the rescue capsule reaching the surface 16 minutes later.^[8][9] Less than 24 hours later, at 21:55 CLDT on 13 October, all 33 miners had been rescued, almost all in good medical condition, and expected to recover fully. Two miners were suffering from silicosis, one of whom also had pneumonia, and others were suffering from dental infections and corneal problems.^[10] Three of the rescued miners had immediate surgery under general anesthesia for dental problems.^[11]

Rescue plans

Miner rescued with a Dahlbusch Bomb, the 1963 predecessor of the Fénix, Wunder von Lengede, artist depiction (1963) by Helmuth Ellgaard

The rescue crews planned to raise the miners one by one with pods. "The mine is old and there is concern of further collapses,” Murray & Roberts Cementation managing director Henry Laas said. “The rescue methodology therefore has to be carefully designed and implemented.”^[12]

Drilling plans

Several types of drilling equipment and different access strategies to reach the miners with escape boreholes were tried in parallel. When the escape shaft reached the miners, there were three plans in operation—the Strata 950 ("Plan A", 702 meter target depth at 90°), the Schramm T130XD ("Plan B", 638 meter target depth at 82°), and a RIG-421 drill ("Plan C", 597 meter target depth at 85°).^[13]

Plan A

Plan A used an Australian built Strata 950 model raise borer^[14] type drilling rig often used to create circular shafts between two levels of a mine without the use of explosives. The drill was provided by South African mining company Murray & Roberts, who had a recently idled machine in Chile for a separate mining contract. The drill had just finished a shaft for Codelco's Andina copper mine in Chile and was immediately transferred to San José. Since it weighed 31 short tons (28 t), it needed to be shipped in pieces. The Strata 950 was the first of the three drills to begin boring an escape shaft.^[15][16]

In traditional raise boring operations, mining companies use a drilling technique known as ‘up-reaming’. Normally, this type of rig first drills a small pilot hole downward, then large machine cutters are attached to the drill which is sticking out the bottom of the pilot hole. The massive cutters are pulled up as they grind through thick rock, boring along the pilot hole. In this case however, since the space below was blocked and the raise bore bit could not be attached from underground, the rig was modified to widen the hole from above.^[12][17]

If the pilot hole had been completed, further drilling would have caused rock debris to fall down the hole, and the miners would have had to remove the debris.

Plan B

Diagram of the rescue capsule "Fenix" class and the miner equipment used in the Copiapó accident of 2010 rescue.

Plan B involved a Schramm Inc. T130XD air core drill owned by Geotec S.A. (a Chilean-American joint venture drilling company) that was chosen by Drillers Supply SA (the general contractor of Plan B) to widen one of the three 5.5 inches (14 cm) boreholes that were already keeping the miners supplied with palomas. Internationally, the drills are used to drill top holes for the oil and gas industry and for mineral exploration and water wells This system employed Chilean Drillers Supply SA (DSI) personnel, Mijali Proestakis (G.M. and Partner), Igor Proestakis (Tech Manager) and Greg Hall (the C.E.O., who joined his team on site for the last eight days of drilling) and their 7" drill pipe air core drill, a team of American drillers from Layne Christensen Co. and specialized Down-The-Hole drilling hammers from Center Rock, Inc., of Berlin, Pennsylvania. Center Rock's president and personnel from DSI Chile were present on site for the 33 days of drilling. While the Schramm rig, built by privately held Schramm, Inc. of West Chester, Pennsylvania, was already on the ground in Chile at the time of the mine collapse, additional drilling equipment was flown from the United States to Chile by United Parcel Service. The percussion-technology hammer drill could drill at more than 40 meters (130 ft) a day by using four hammers instead of one.^{[12][18][19][20]}

The Schramm T-130 was directed to bore toward the workshop, a space that was accessible by the miners. The T-130 became operational on 5 September and worked in three stages. First, it needed to enlarge the 5.5 inches (14 cm) hole to a 12 inches (30 cm) hole. It then needed to drill the 12 inches (30 cm) hole into a 28 inches (71 cm) diameter hole. “If we tried to drill from a 5.5 inches (14 cm) hole to a 28 inches (71 cm) hole, the torque would be too high and it would ... put the drill bits under too much pressure,” said Schramm, Inc. Latin American Regional Manager, Claudio Soto. However, by reusing the same hole, there was still added pressure on the drill. Delays occurred because of issues with the neck of the drills caused by the angle of the drilling. Rescuers couldn’t drill vertically since that would require placing the heavy rig on the unstable ground where the cave in had happened. And the rescuers also had to avoid drilling into the production tunnels that wind above the shelter. Soto added, during the rescue, “It’s a difficult hole. It’s curved and deep. The hard rock has proven to be abrasive and has worn out the steel of the drill.”

The fine rock debris, known as cuttings, fell down the pilot hole; an estimated 500 kilograms (1,100 lb) of rocks fell down every hour. Working in shifts 24 hours a day, the miners had to keep the passage clear with the industrial-sized battery-powered sweepers, shovels and wheel barrows trapped in the mine with them.^[21] The miners had to remove on their own a total mass of drilling cuttings estimated at up to 700 metric tons (770 short tons), considering a borehole diameter of 70 centimeters (28 in), with a depth of 688 meters (2,257 ft) and a rock density of 2.7 tons per cubic meter.^[12][22]

Its first delay was caused by it hitting a metal bar in an old working and wrecking.^[23] The wrecked drill bit was retrieved by sending down a steel tube called a "spider", whose end was cut into 8 traight and long teeth. When the spider reached the obstruction, the 8 teeth bent down around the drill bit, and on further pressure bent in below the drill bit, thus holding on to the bit and allowing it to be hauled up to the surface. The second delay was caused by the replacement drill bit wearing out. As the drill drilled down, the spoil fell down the pilot hole and the trapped miners had to clear it away, using a front loader, fueled with diesel sent down via one of the supply holes.

Plan C

Plan C was a powerful Canadian built RIG-421 oil drilling rig operated by Calgary-based Precision Drilling Corporation and was the last drill to become involved in the rescue process; it began drilling on Sept. 19.^[12] The rig is a special drill used for oil and gas drilling that could drill a wide enough escape shaft in a single pass without a pilot hole. RIG-421 is a Diesel-Electric Triple that was 43 meters (141 ft) tall and needed 40 truckloads to bring its pieces from Iquique, Chile to Copiapó. 10,000 cubic meters (13,000 cu yd) of rock and gravel were cleared to make a stable platform for it on the rough hillside. It was chosen for the rescue operation because it can drill large holes deep into the ground and because it works faster than mining drills. Unlike the Strata 950 and the Schramm T-130, the Rig 421 brings debris back up to the surface.^[12][24]

It suffered a setback due to the difficulty of aiming the larger drill at a 2.5m x 2.5m target and the hardness of the rock when the drill diverted from its course. The drill then needed to be removed, resized and repositioned, which slowed its progress.“We’ve drilled wells all around the world. The actual drilling of the hole in the ground isn’t that difficult. When you’re given a target to aim for it’s a little more difficult,” said Shaun Robstad, superintendent with Precision Drilling. Many family members of the miners once had high hopes for this Canadian rig, but it had to reduce its drill size and lagged behind.^[12][25][26]

Drilling results

The widened shaft of Plan B's Schramm T130XD reached the trapped miners at 08:05 CLDT on 9 October after a 10-hour stoppage to change the drill-bit.^[27] By 8 October, the Plan A Strata 950's pilot hole had reached 598 meters (1,962 ft) deep (7001850000000000000♠85% - it had not yet started its widened shaft). Plan C's RIG-421, the only machine at the site which drills a shaft wide enough immediately, reached 372 meters (1,220 ft) (7001620000000000000♠62%).^[12][28]

As illustrated in the graphic to the right, it was the Schramm T-130, Plan B, that reached the miners on Oct. 9. The rescue operation was an international effort. The rescue of the miners involved not only technology, but the cooperation and resources of companies and individuals from around the world, including Latin America, South Africa, Australia, the United States and Canada. NASA specialists helped develop a sophisticated health agenda. Canada brought in their “Plan C” drill. An Austrian system of cranes and pulleys designed for the rescue capsule eventually pulled the miners to the surface. But overall, it was widely a Chilean-led team and effort. As one NASA specialist said while visiting early on in the rescue: “The Chileans are basically writing the book.”^[12]

See also

• Quecreek Mine Rescue involved a similar rescue capsule in Pennsylvania, July 2002 to rescue a trapped mining crew.
• Dahlbusch Bomb

References