What is room and pillar mining?
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Room and pillar mining is a method of underground mining that involves excavating a network of rooms, or “stopes,” separated by pillars of uncrushed rock. The pillars are left in place to support the roof of the mine and prevent it from collapsing.
In room and pillar mining, the ore is extracted by creating a series of rooms, or stopes, connected by horizontal or slightly inclined tunnels. The ore is extracted from the stopes, and the pillars are left in place to support the roof of the mine. This method is used to extract coal, as well as other minerals such as salt, gypsum, and potash.
Room and pillar mining is typically used for relatively shallow deposits, and it is a good choice when the ore body is relatively flat and horizontal. It is also a good method to use when the ore body is too small to justify the construction of a longwall mining system.
The main disadvantage of room and pillar mining is that it can be less efficient than other methods, such as longwall mining, because it leaves a significant portion of the ore body untouched. This means that more rock must be moved in order to extract a given amount of ore, which can be more time-consuming and expensive
⚒ Room-and-pillar mining
◽️In this method, a number of parallel entries are driven into the coal seam. The entries are connected at intervals by wider entries, called rooms that are cut through the seam at right angles to the entries
◽️ The resulting grid formation creates thick pillars of coal that support the overhead strata of earth and rock.
⚫️ There are two main room-and-pillar systems,
▪️the conventional
▪️ the continuous.
◽️In the conventional system, the unit operations of undercutting, drilling, blasting, and loading are performed by separate machines and work crews.
◽️In a continuous operation, one machine—the continuous miner—rips coal from the face and loads it directly into a hauling unit.
➡️ In both methods, the exposed roof is supported after loading, usually by rock bolts.
◽️Under favorable conditions, between 30 and 50 percent of the coal in an area can be recovered during the development of the pillars. For recovering coal from the pillars themselves, many methods are practiced, depending on the roof and floor conditions.
◽️The increased pressure created by pillar removal must be transferred in an orderly manner to the remaining pillars so that there is no excessive accumulation of stress on them. Otherwise, the unrecovered pillars may start to fail. endangering the miners and mining equipment. The general procedure is to extract one row of pillars at a time, leaving the mined-out portion, or gob, free to subside. While extraction of all the coal in a pillar is a desirable objective, partial pillar extraction schemes are more common.
◽️At depths greater than 400 to 500 meters, room-and-pillar methods become very difficult to practice, owing to excessive roof pressure and the larger pillar sizes that are required.