The Chilean mine rescue continues with 4 men out.

I am sitting watching the rescue of the miners from the copper/gold mine in Chile. Four of the miners have been brought to the surface so far. These were some of the fittest of the men trapped, to make sure that if, in the early stages of the use of the travelling cage, that they could handle any mishaps. And after three rescue personnel rode the cage into the mine, it is now being lowered empty.

The event is being handled with some skill by the Chilean government, they had a camera feed from the bottom of the mine. Thus we saw the rescue cage arrive at the bottom of the mine, and the first of the rescue team get out to help with getting the men out. The trip down takes just over ten minutes, then the harness which the man in the cage wears (which carries an oxygen feed, and also can provide a support since it is hooked to the top of the cage) is removed and passed to the next man to be rescued. He is already wearing a coverall that was made to his measurements, and a jacket (given the move from the heat of the mine to the cold of the desert night at the surface). After donning the harness he is fitted into the cage, the door is closed, and the cage slowly lifted back into the shaft. (It is long enough that it does not come completely out at the bottom and at the top and bottom has spring-loaded wheels that roll on the walls as it moves up and down). It takes fifteen minutes to get to the top, and the rider has a headset so that he can talk to the surface crew while ascending.

So far there has been no glitches in the process, the President of Chile is on hand to greet the miners, and the second one out presented him with a rock from a bagful that he had brought out for the top folk present. And after greeting the dignitaries and a couple, at most, family members the rescued men lie on a gurney and are taken for medical examination. (The fourth man to ride to the surface had only been working in the mine for 5 days and was from Bolivia).

In the chat that the program hosts carry on to fill in the time that the cage is travelling, they talked about the debt that the world owes to miners. These men went on shift on August 5th, working in an old (over a hundred years old) and over-mined deposit and were trapped for 69 days. They are talking about changes that will come about as a result of this, but so often a month after the rescue, it fades into history without much change. Over a hundred years ago in Northern England virtually the entire male population of the mining village of Hartley were killed when the only shaft into the mine was blocked. Yet here this mine had only one effective exit. The second nominal exit, up a ventilation shaft, had no ladder all the way up, and so was not available, though the miners did try it to see if they could get out.

In this case the rescue was helped by the mining and drilling community from around the world. Three different machines were used to drill the holes for the rescue shaft. The speed with which it was done hides the complexity of the job that was achieved. Bear in mind that when the rescue began it was expected to take until Christmas.

There were only two T-130’s in Chile, (the machine that drilled the successful shaft) and there were only certain sized pipe sections available, and so it was a case of working out how to get it done with equipment that had never been used for this before. There were a couple of times when it seemed they might not be able to do it, there was a pause of some four days because of problems with the bit in trying to drill the hard rock, but they worked through it. And they were successful., even though they had to drill around the winding drilled hole that had been drilled first to intersect the rescue area. It required that they bring in the best crew that they could find, and that included flying one driller in from Afghanistan where he had been working drilling water wells. It is likely the most difficult job that they have faced, and this has largely gone unremarked in the media.

Given that the technology was successful there is some talk of developing a permanent set of equipment that can be moved to the site of any future mining disaster, and building on the lessons learned with this event, be better prepared to create access to anyone trapped. This sort of effort will continue to be necessary. Miners work at a considerable distance, normally, from the access shaft through which they enter and leave the mine. In most operations the area around the shaft is left un-mined so that it supports the shaft walls and holds their integrity. This was another safety precaution apparently abandoned in this instance. But it means that miners have to travel some distance to get to the working area, and when disaster strikes they may be a long way from that safe passage out.

Mining will thus remain a dangerous occupation, perhaps even more so in the future. For just as we are now seeing, as the ASPO conference last week noted, the approach of peak oil, so we are also approaching peak minerals. As with oil, the need for future supplies means that smaller and more difficult and dangerous deposits will be worked. In order to save on cost risks will be taken, and men will be trapped and die. It is, sadly, a price that the bulk of society seems quite willing to pay. Fortunately in this case that price does not have to be paid, but unfortunately in too many parts of the world it is still being paid on far too often a basis. And as the need for miners and the minerals and fuels that they produce continues to grow it is hard to see that situation changing much. The 1,500 journalists who are in the desert, without decent accommodation and amenities will soon leave, I would not be surprised, after a while, to hear that miners were back, working in much the same conditions as before. The world need and the money that it will be willing to pay will be incentive enough.

Coal Mining - robbing the pillars

In recent posts I have written about room and pillar mining, where the miners drive tunnels through the relatively horizontal coal seam, until they come to the edge of the property. Depending on the accuracy and honesty of the mine surveys, they then stop. I mention this latter because, on occasion, miners who later worked in an adjacent mine, thinking that they have plenty of room, have worked close to the boundary on the other side, and suddenly, and often tragically, have found that they were too close. Water or gas that had collected in the old workings flooded into the new ones, with usually fatal results. (The Quecreek Mine Rescue was an exception).

Once the mine has reached the boundary, there is still a lot of coal left in the pillars. If the mine tunnels are 15 ft wide, and the pillars are 45 ft wide and the coal is 6 ft thick, then using a rough rule that a cubic yard of coal weighs a ton, gives that the original tonnage between the tunnel center-lines, assuming square pillars, would be 800 tons (20x20x2). The pillar left contains 450 tons, so that the initial extraction only removed 44% of the coal and 56% remains in the pillars. So, providing that the mine does not have major surface construction that would be harmed if the ground subsided, the miner might choose to remove some of that coal, as he retreats back from the boundary. (Although David Kuchta will tell you of times when folk were less fussy about worrying about the houses on the surface).


This practice is known as “pillar robbing,” though to get away from the negative picture that this raises, it may be called “pulling” or “drawing” the pillars. Essentially the miners will start at the boundary and work back towards the shaft, removing coal from the pillars in a systematic pattern as they go. And if you pull out the supports that hold the roof up, then that roof will collapse into the opening beneath it.

This is where there is some skill and forethought required in planning how to mine out the pillars, and to control the way in which the roof breaks. If the pillars are pulled properly, then the coal that is left, because some is, will crush sufficiently slowly that the miners can have enough warning to be out of the way, and it will control the way that the roof breaks.

The process can be illustrated by first showing the layout I used earlier for the development of the mine:

Overview of a working room and pillar section

And then look at a mining plan after the mine has pulled most of the pillars from a section.


With 80% extraction the mine is now only leaving 160 tons of coal behind in the fenders or stumps. Fenders are usually the larger pieces of pillars that are left along the edges of the path the machine must move along, stumps are the residuals in the body of the pillar.

As the miner removes the coal, to keep the operation safer, while the coal is being removed, wooden props used to be installed that would hold the roof in place.


That practice, with the men under unsupported roof is no longer used. Now the coal is extracted using, increasingly, remotely operated mining machines, with the supports more closely located around the mining area and increasingly being hydraulic.

Pillars can either be mined very simply, by cutting into the side of the pillars left in initial mining:

Simple pillar removal sequence SME handbook

The small black circles are where the props (historically wood but now hydraulic props) are located.


Pocket and wing mining – the pockets are removed in sequence, the wings are left to hold up the roof.

In stronger coals or where the roof is better more of the coal can be removed.

Sequence of coal removal (SME Mining Engineering Handbook Vol 2)

The reason that the props are located close together at the edges of the remaining rooms, is that the roof layers above the area will start to break after the coal is removed. By establishing the props along the edge of the pillars the breakup from the previous coal removal will be stopped at the edge of the existing pillars.

The roof breaks into fragments as it falls, and will bulk into the space left by the coal removal. This bulked up rock provides some support to the roof overlying the area where the coal is then removed in the next sequence of mining. And so the process retreats.

It is not as effective as getting all the coal out, and can lead to more difficult problems at the surface than an alternate method of mining called longwall, and we’ll come to that next. But pillar robbing requires a great understanding of the geological conditions before it can be safely carried out. Unfortunately when this is not the case then we get disasters such as that at Crandall Canyon.