The Engineering behind Chilean Miners’ Rescue Effort

Earlier this month, over a billion people (myself included) watched as the thirty-three Chilean miners who were trapped in a copper-gold mine were finally rescued after spending a record 68 to 69 days underground. The rescue mission’s objective was to dive 2,300 feet below the Earth’s surface at a distance of about 5km from the main entrance. The challenge was to navigate the irregular spiral turns of the mine (unlike a vertical mine shaft) without disturbing the geological structure of the mountain.

Several institutions including the Chilean government, Codelco, the state owned mining company, NASA and various drilling companies from Canada, Australia, South Africa and the US attempted to find survivors. However, the miners were trapped for a total of 17 days without contact in the mineshaft after failing to escape through the ventilation system. At a risk of causing more geological movement and endangering the miners further, the crew working on rescuing the miners abandoned using the ventilation shaft as well.

Eight exploratory boreholes were drilled in strategic points around the mine to try and locate the miners under the supervision of Engineer André Sougarret, head of the El Teniente Mine of Codelco. Some of the issues during the first phase of the rescue mission were the sensitive nature of the geological formation of the mountain and the rock hardness which caused the drills used to drift from their intended path. The eighth borehole drilled (with a diameter of only 5.9in) finally reached the survivors on the 17^th day after the collapse about 20m away from the emergency shelter. A note written by the miners confirmed the survival of all 33 miners reached the surface later that day.

After discovering the location of the miner’s emergency shelter, video camera and materials were sent down in 5 foot long plastic capsules called palomas (which means carrier doves) that took an hour to reach the miners through the eighth borehole. The engineers coated these capsules with a gel in order to ease the passing of these capsules through the borehole. High energy glucose gels (to reduce stomach ulcers from food deprivation), rehydration tables, water purification tablets, medicine and oxygen (when there was an air deficiency) were sent down in these tubes. Delivery of solid food occurred a couple of days later after the miners became accustomed to eating more especially after the long period of starvation during the first 17 days. Two additional boreholes were drilled for oxygen and videoconferencing equipment before the start of the rescue operation actually began.

While construction of the capsule used to rescue the miners began, the miners were provided with emergency supplies (some provided by NASA) and devices that imitated life above ground to keep miners’ mental health, which at this point was more important, stable. Fluorescent lights with timers were sent down the capsules to imitate day and night so that the miners could have a perception of time. Psychologists believed that the miners should feel in charge of their situation, thus the miners were given the chance to organize themselves into groups that were responsible for various tasks that needed to be completed underground. NASA’s involvement in this process was paramount since the miners’ situation greatly reflected similar situations experienced by the astronauts who have spent months on end in the space station.

The actual plan to get the miners out of the mineshaft consisted of raising each miner, one by one, in specially designed pods. The major constraint surrounding this problem was the size of the hole being drilled and its effect on the instability of the geological conformation of the mountain. Thus, the rescue method had to be meticulously planned since any major error would have seen catastrophic results for the miners.

Many different strategies and materials were used simultaneously to reach the miners. When the miners escape shaft reached the miners, three plans, being Plan A, Plan B, and Plan C were in operation at the same time. Each plan was tested for its strengths and weaknesses at which the best plan was executed in the miner rescue effort.

Plan A consisted of an Australian built Strata 950 model raise borer type drilling rig that is usually used to create circular shafts between two levels in a mine without the use of explosives. The drill was provided by a South African company and was the first of the three drills to begin boring the escape shaft. The method worked to drill a small hole first in which the large cutters were attached to the drill which stuck out the bottom of the hole. Then, the cutters were pulled up to grind the rock upwards. Since there was no space below the drill, the rig was modified so that it was wider above in order to provide some “give” when drilling around the pilot hole. The debris fell at a rate of 500kg an hour in which the miners themselves had to remove with the equipment they had trapped with them.

Plan B involved a Schramm Inc. T130XD air core drill owned by Geotec S.A (a Chilean-American joint venture). This drill was used to widen one of the three boreholes that were used to keep the miners supplied with palomas. It had to enlarge the hole in three stages where the hole was progressively made bigger. This ensured that the rock formation was able to take on the necessary pressure. At this stage, there were many delays; the first was the drill hitting a metal bar and the second was the replacement drill bit wearing out. These delays were all taken care of by using a “spider” to retrieve the metal bar and the drill bit being replaced.

Plan C involved a powerful, Canadian built RIG-241 that had the ability to drill a wide enough escape shaft without the need of a pilot hole. This oil drilling rig was operated by Calgary-based Precision Drilling Corporation which brought debris back up to the surface unlike the other drills. The hardness of the rock and the size of the drill proved to be a major setback due to the constant need to reposition the drill as the drill strayed when trying to drill on the target.

The drill that reached the miners first was Plan B which broke through to the shelter on October 9^th. The rescue capsule made while the drills were making the escape shaft was 66cm in diameter; thus, the miners could not have a waistline greater than 90cm if they were to escape the mine. The steel rescue capsules dubbed Fénix 1, 2 and 3 (Phoenix in English) were constructed by the Chilean Navy with help from NASA. 75 of the design features for the three capsules included an oxygen tank, technology to cut down the friction while in the escape hole and the ability for each miner to strap himself in easily. The Fénix 2 used to rescue the miners had an oxygen supply, lighting, video communication, a reinforced roof in case a rock fell and an escape hatch with a safety device to allow the miner to lower himself to the mineshaft if the capsule got stuck.

After the necessary preparation for the extraction of the miners was made, the rescue effort, named Operación San Lorenzo (Operation St. Lawrence) after the patron saint of the miners, began on October 12^th. The fittest in body and mind were the first four miners extracted with the least healthy to the healthiest men coming afterwards. The miners were all required to exercise beforehand, eat liquid only diets, to wear sunglasses and wear a girdle at the time of the ascent. The sunglasses were needed to protect the miners’ retinas due to the extended period in which they remained in the dark while the girdle was used to reduce the effect of the pressure changes when making the ascent.

The magnitude of international support and engineering prowess for this immense operation was astounding since many different aspects of science and engineering were used simultaneously to allow the miners to escape relatively unscathed. Not only was there support from major corporations and institutions around the world, the emotional support that poured in for the miner’s was, in itself, nostalgic. Then again, the miners’ ability to work together towards a common goal of survival was, if anything, inspiring.