Sequence of coal removal ( SME Mining Engineering Handbook Vol 2) In stronger coals or where the roof is better more of the coal can be removed. Pocket and wing mining – the pockets are removed in sequence, the wings are left to hold up the roof. The small black circles are where the props (historically wood but now hydraulic props) are located. Simple pillar removal sequence SME handbook Pillars can either be mined very simply, by cutting into the side of the pillars left in initial mining: 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. ![]() That practice, with the men under unsupported roof is no longer used. 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.Īs 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. With 80% extraction the mine is now only leaving 160 tons of coal behind in the fenders or stumps. Overview of a working room and pillar sectionĪnd then look at a mining plan after the mine has pulled most of the pillars from a section. The process can be illustrated by first showing the layout I used earlier for the development of the mine: 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. 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. And if you pull out the supports that hold the roof up, then that roof will collapse into the opening beneath it. 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. 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. (Although David Kuchta will tell you of times when folk were less fussy about worrying about the houses on the surface). 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. The pillar left contains 450 tons, so that the initial extraction only removed 44% of the coal and 56% remains 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). Once the mine has reached the boundary, there is still a lot of coal left in the pillars. (The Quecreek Mine Rescue was an exception). Water or gas that had collected in the old workings flooded into the new ones, with usually fatal results. 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. Depending on the accuracy and honesty of the mine surveys, they then stop. 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.
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