The Schramm T-130 drill, known as plan B, has started drilling the final 330ft (100m) to widen a borehole for a metal rescue capsule that will raise the men from the deep chamber where they have been trapped since Aug 5.
Laurence Golborne, Chile’s mining minster, announced on a visit to the San Jose mine yesterday that he expected the breakthrough to come overnight on Friday. The men could be lifted to the surface as early as Monday.
“We are advancing pretty well on plan B,” Mr Golborne said. “We are hoping to break through more or less by daybreak this Saturday but depending on whether we have to change the hammer or not it could be a little earlier.”
The team of engineers must then decide how much, if any, of the 2,067ft borehole needs to be lined with metal casing, a process that could extend the miners’ confinement for another eight to 10 days.
The casing would serve to reinforce the walls of the shaft, limiting the risk of collapse, and would also act as buffer between the capsule and the shaft, resulting in a smoother journey to the surface.
“The final decision [on the casing] will be taken once we have broken through,” Mr Golborne said. “If none is needed it could take two to three days depending on installation of the rescue platforms. ”
Experts warned that inserting the lining could be a challenge in itself because the shaft curved between the depth of 330ft and 395ft.
A winch capable of lifting 400 tons must be installed on a platform over the shaft to lower in the tubing, but an accident could send tons of steel hurtling downwards or cause a section to get stuck part way down, blocking an exit route that has taken more than a month to drill.
“It seems likely that we will have to put in the casing at least for the first 330ft,” said Rene Aguilar, the rescue co-ordinator. “If we could do the lining for all the hole, of course, we are going to do it. We have to reduce the risk of this operation.”
Family members have been briefed on the decision-making process and said they were prepared to wait. “We want to have the shaft lined if that seems safer,” said Juan Carlos, the nephew of Jose Ojeda, a trapped miner. “We have been waiting for so long that one or two more days is nothing.”
When rescue day arrives, the miners will be brought to the surface in a bullet-shaped pod designed by the Chilean navy’s shipyards and nicknamed Phoenix.
Three extra capsules have been brought to the site as reserves. Rescuers will use an Austrian-made hoisting system of pulleys and cranes to lower the cage down the shaft and extract the miners one at a time.
Each round trip will take from an hour to 90 minutes, with the entire operation lasting an estimated 37 hours. Should a miner hit a snag during the ascent, he will be able to lower himself back to the shelter using wheels on the sides of the capsule.
A team of 16 men given the task of the final stage of raising the men to the surface were practising for every possible scenario yesterday.
The miners have been told of their imminent rescue. “They can hear the drill approaching and are fully informed of the progress and what comes next,” said Alberto Iturra, chief psychologist at the site.
“We are entering the final days before they are reunited with the world above and it’s exciting for everyone,” he added. [via MS NBC]