Officials battling to rescue the 33 miners trapped underground in Chile for the past two months are planning to insert steel piping that can withstand tons of pressure into the shaft to prevent collapses during the operation.
A team of engineers are currently working out whether they can push the 12m sections of pipe through curves in the shaft without having the welds crack. Tons of steel could be sent down into the shaft or get stuck halfway down, blocking an exit that has taken more than a month to drill, if the operation fails.
Rescue co-ordinator Rene Aguilar said: “The first choice is to put the casing. We have to put the casing at least for the first 100 metres. If we could do the lining for all the hole, of course, we are going to do it, of course. We have to reduce the risk of this operation.”
Lining the top 100m of the shaft – which passes through a particularly fractured section – would take about 15 hours, with the full operation expected to take about 60 hours. Any miner needing urgent medical care could be pulled up in the next few days, although Aguilar said the full rescue effort will not begin until after October 15.
Others involved suggested that plan itself is risky, largely due to gradual curves in the “Plan B” shaft being drilled by the T130 machine, which is the closest to being completed. It starts like a waterfall plunging off a cliff – gradual at first and then bending nearly straight down. Getting straight pipe through the curve is the challenge.
An engineer, speaking on condition of anonymity, said: “The pipe, by virtue of its own weight, bends a little; it has a certain flexibility. But when you weld two sections together and insert it in the hole, the weld doesn’t bend; it’s rigid, hard. And so the question is whether it will withstand the stress of the curve. If they decide to encase it completely – all 624m – you’re talking about a tube that weighs 130t.”
The pipe is made of 1.27cm-thick steel, 61cm wide on the outside and 58cm wide on the inside. Each section would be inserted into the shaft with an enormous crane that arrived at the mine on seven huge trucks to applause from relatives who have held vigil on the dusty Atacama desert hilltop since the men were trapped on 5 August.
The risks cannot be calculated until the shaft is inspected with a video camera, said Brandon Fisher, president of Pennsylvania-based Center Rock, which makes the drilling system being used on the T130. Fisher said: “My opinion is they’re going to try to run the casing, but when you’re running casing in an angled hole like this, it’s very, very difficult to make that happen.”
The T130 paused at 519m on Wednesday to change its drill bits, leaving just over 100m to go in a final push that will likely reach the miners on Friday. The final section of the hole will narrow to 66cm wide to minimise risk of a rockfall during the final drilling, leaving just four inches of leeway to push the pipe all the way through.
Omar Gallardo, a professor of mining engineering at the University of Santiago, favours inserting the pipe. He said: “With the available information, and to not run any risk at all, I would encase it. It would be less risky for the miners. They’ve been down there for 61 days. Giving them a few more days down there in exchange for being able to pull them out safely is preferable.”