Women waiting for mine rescue

Chile's great mine escape

Engineering is playing a vital part in the race to rescue 33 men trapped in Chile's San Jose mine.

'I am 33 years old, we are 33 miners, and Jesus died at the age of 33 - a great coincidence for a great miracle.' So read Victor Zamora's emotional note to his mother. He and his fellow miners are still waiting to be rescued from 700m underground at the San Jose mine in northern Chile.

Chile does indeed seem predisposed to produce the kind of miraculous survival stories that make great plotlines for your typical Hollywood thriller. It happened in 1993 with the release of 'Alive', the film narrating the story of a group of Uruguayan rugby players who, following a plane crash into the snow-covered Andean mountain range in 1972, survived for 72 days by turning to cannibalism.

Should everything go according to plan at the San Jose mine, there is talk already of - if not a lucrative Hollywood deal (highly premature and distasteful before the longed-for happy ending) - then certainly the sheer forces of drama at play in this compelling news story.

But before Zamora can truly feel born again - before the world can refer to the 33 trapped gold and copper miners as another great Chilean story of survival against all odds - there is an awful lot of work to be done, and plenty of things that could go fatally wrong.

Tasked with the mission of getting everyone out as soon and as safely as possible - while at the same time providing logistical, physical and mental support to endure the long wait - an army of engineers, geologists, scientists, doctors and technicians are working around the clock. It has been estimated that, for each trapped miner, there are currently 10 full-time professionals offering their expertise.

As soon as contact was established with the missing miners on 22 August (following a rock collapse 17 days earlier), a plan was swiftly devised to engineer an escape route from the emergency refuge where the workers had been located.

With an estimated 700,000t of collapsed rock and very unstable subsurface conditions, any attempt to free the men by sending human rescue teams into the heart of the mine was ruled out as too dangerous.

Plan A

Just as with the technique used to lower the probe that made initial contact with the miners, it was established that the only viable way to mount a rescue operation would be by drilling a borehole from the surface. But, unlike the boreholes that had been drilled during the search stage, which were only 16cm in diameter, it was obvious that any rescue well bore would need to be at least 66cm in diameter.

That's the minimum width that would allow for a metal cage (transporting one man at a time) to be lowered and raised during what's expected to be the most dramatic part of the operation. That's also the reason why the duration of the overall rescue mission was always measured in months rather than days or weeks.

Drilling of the first shaft began on 30 August. Now known as 'Plan A' among the engineering team, it will be a 90 degree angle, vertical borehole with a target depth of 702m. The drilling rig used for this well, which is positioned next to the ventilation shaft of the mine, is a Raise Borer Strata 950 supplied by Codelco, Chile's state-owned copper mining company.

As of 7 September, the machine had managed to drill the first 113m of stage one of the well. Stage one consists of drilling a 38cm diameter hole to target depth. Once the drill bit penetrates the roof of the tunnel next to the exit of the refuge, tonnes of drill cuttings will begin to fall into the tunnel. The trapped miners will be asked to remove the debris using wheel barrows and battery-powered sweepers left inside the mine.

Only then can stage two of Plan A begin, which consists of widening the shaft to 70cm (this time from the bottom up) using a drilling head. This will produce significantly more debris accumulation in the tunnel, which again the miners will need to clear in round-the-clock shifts.

Depending on the integrity of the well bore, engineers will then have to decide whether or not a potential stage three is needed. Stage three would encompass casing the well with steel tubes to reinforce its walls. However, Andre Sougarret, the chief engineer overseeing the rescue operation, is confident that there won't be a need to case the well 'because the rock is really high-quality, really strong,' he says.

Miguel Fortt, a local mining engineer specialised in probe drilling who in a career spanning 43 years has drilled over one million kilometres worldwide, is acting as a key technical consultant and helping design the capsule that will be used to rescue the workers.

Asked about the strict protocol that rescuers and miners will follow once the borehole is completed, the capsule fitted to the cable that will pull it and the performance of the lift tested, the engineer replies: 'First the rescuers will go down. They will be in charge of getting the miners out one by one. They will help them get inside the cage while they reassure them. They will make sure all protective equipment is correctly used, they will switch the capsule lights and communications equipment on and will teach the miners how to use the emergency oxygen system.'

A predetermined order based on individual medical records will be used to prioritise the evacuation of the mine. Each journey up will take between one and three hours. Miners will be blindfolded to avoid the bright sunlight of the Atacama Desert damaging their eyesight following months of underground isolation.

Plan B ...and C

While Plan A was the first to move into what the drilling industry calls the 'development phase', at least two other boreholes have been designed in an effort to both add redundancy and maximise the chances of a faster rescue.

Plan B went into development on 5 September and had reach 123m two days later. For this second bore hole, a large Schramm T-130 drilling rig supplied by Geotec is following a similar three-stage strategy to gradually widen the well diameter and potentially case its walls. While both the Strata 950 used in Plan A and the T-130 E F used in plan B operate at similar speeds, there are two differences that mean that the Plan B drilling crew might get the job done faster.

The first one is that, unlike the first well, stage one of Plan B doesn't involve drilling from scratch. Instead, it consists of enlarging one of the three bore holes that were until recently used to send supplies to - and communicate with - the miners. The second difference is that there will be less drilling to do, as this shaft starts from a lower point on the mountain and leads to a workshop located several levels above the refuge. Still, the 82 degree inclination of the shaft means that target depth for Plan B is 630m.

Then there's what could turn out to be an even speedier escape route for the trapped miners. Aimed at a ramp located above the workshop, the Plan C bore hole will be drilled to a target depth of 598m. ENAP, Chile's state-owned oil producer, is heading the operation.

'Unlike the two other machines, this one doesn't require two or three different runs [of the drill string],' Sougarret explains. 'As soon as the borehole is drilled, it is immediately cased.' Sougarret's comments suggest the engineering behind Plan C would be based on a relatively novel technology in the oil and gas industry, known as 'drilling with casing'.

While such a technique can indeed decrease drilling time, it also requires the levelling of a field the size of a football pitch so that a 45m-high tower can be erected. 'The performance of the rig would allow us to complete the well in only one and a half months,' Sougarret says. However, drilling is unlikely to begin before 18 September.

The capsule in which the miners will be lifted is being built to be 'tripped' through whichever borehole is finished first. Assuming that Plan C has the greater chance of beating the other two - and that no drilling problems are encountered, which is unlikely but not impossible - the miners could be looking at an late-October rescue date in the most optimistic of circumstances.

Down the tubes

Beyond drilling, there are several other aspects of the complex rescue mission in which engineers are playing an equally vital role. One is communication: the process of' exchanging information between miners and the outside world has been increasing in sophistication ever since 22 August.

That day, short messages were briskly written down in small pieces of paper (such as the one president Piñera famously held in a plastic bag containing the words 'we're all OK in the refuge') and attached to the end of a probe. This most basic of systems was significantly improved a couple of days later with two parallel developments.

The first was the installation of a capsule shuttle system (using two of the narrow ducts made during searching), which allowed rescuers and family members to exchange long letters with the miners. The second enhancement was the deployment of a basic telephone line for audio communications, which was later upgraded to add a videoconferencing link.

Of the three initial boreholes that managed to make contact with the miners: one is being used (as said above) to guide the Plan B drilling towards the workshop; another one will keep sending supplies to the miners; and the remaining one is being turned into what the rescue team calls a 'poliduct'.

This multi-purpose channel will provide the miners with not only fibre-optic communications but also electricity, running water and oxygen. The miners have been using a small air quality monitoring device that rescuers managed to squeeze through the narrow tube in late-August.

Other devices that they were able to send included portable music players, pico-projectors for video reproduction (accompanied by foldable video screens), health monitoring equipment collapsible beds.

They might be enduring constant temperatures of over 30C, unbearable humidity, no sunlight and no fresh air. Then again, this new Chilean story of miraculous survival is not set in the 1970s but in the anywhere-anytime-anyhow 2010s.

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