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Room and pillar mining
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Room and pillar mining
Room and pillar or pillar and stall is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out while "pillars" of untouched material are left to support the roof – overburden. Calculating the size, shape, and position of pillars is a complicated procedure, and an area of active research. The technique is usually used for relatively flat-lying deposits, such as those that follow a particular stratum. Room and pillar mining can be advantageous because it reduces the risk of surface subsidence compared to other underground mining techniques. It is also advantageous because it can be mechanized, and is relatively simple. However, because significant portions of ore may have to be left behind in the pillars, recovery and profits can be low. Room and pillar mining was one of the earliest methods used, although with significantly more manpower.
The room and pillar system is used in mining coal, gypsum, iron, limestone, and uranium ores, particularly when found as manto or blanket deposits, stone and aggregates, talc, soda ash, and potash. It has been used worldwide from the Czech Republic to Canada, to China to the US.
Planning for the development of room and pillar mines operates in much the same way as other mining methods, and begins with establishing ownership of the mine. Then the geology of the mine must be analysed, as this will determine factors like the lifespan of the mine, the production requirements, and the cost to develop and maintain.
Next, mine layout is determined, considering factors like ventilation, electrical power, and haulage of the ore in cost analysis. Due to the non-homogeneous nature of mineral deposits typically mined by room and pillar, mine layout must be mapped very carefully. It is desirable to keep the size and shape of rooms and pillars consistent, but some mines have strayed from this formula due to lack of planning and deposit characteristics. Mine layout includes the size of rooms and pillars in the mines, but also includes factors like the number and type of entries, roof height, ventilation, and cut sequence.
Room and pillar mines are developed on a grid basis except where geological features such as faults require the regular pattern to be modified. The size of the pillars is determined by calculation. The load-bearing capacity of the material above and below the material being mined and the capacity of the mined material determines the pillar size.
Random mine layout makes ventilation planning difficult, and if the pillars are too small, there is the risk that they will fail. In coal mines, pillar failures are known as squeezes because the roof squeezes down, crushing the pillars. Once one pillar fails, the weight on the adjacent pillars increases, and the result is a chain reaction of pillar failures. Once started, such chain reactions can be extremely difficult to stop, even if they spread slowly. To prevent this from happening, the mine is divided into areas or panels. Pillars known as barrier pillars separate the panels. The barrier pillars are significantly larger than the "panel" pillars and are sized to allow them to support a significant part of the panel and prevent progressive collapse of the mine in the event of failure of the panel pillars.
Traditionally, the act of mining consists of three steps. First, the deposit is "undercut", where a slot is cut as deep as possible along the bottom of a section of ore. This undercut allows for a manageable pile of rock in later stages. The second step is the drilling and blasting of the section. This creates a pile of ore that is loaded and hauled out of the mine—the final step of the mining process. More modern room and pillar mines use a more "continuous" method, that uses machinery to simultaneously grind off rock and move it to the surface.
Other processes, such as backfill, where discarded tailings are unloaded into mined-out areas, can be used, but are not required. Retreat mining (below) is an example of a process like this.
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Room and pillar mining
Room and pillar or pillar and stall is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars. To do this, "rooms" of ore are dug out while "pillars" of untouched material are left to support the roof – overburden. Calculating the size, shape, and position of pillars is a complicated procedure, and an area of active research. The technique is usually used for relatively flat-lying deposits, such as those that follow a particular stratum. Room and pillar mining can be advantageous because it reduces the risk of surface subsidence compared to other underground mining techniques. It is also advantageous because it can be mechanized, and is relatively simple. However, because significant portions of ore may have to be left behind in the pillars, recovery and profits can be low. Room and pillar mining was one of the earliest methods used, although with significantly more manpower.
The room and pillar system is used in mining coal, gypsum, iron, limestone, and uranium ores, particularly when found as manto or blanket deposits, stone and aggregates, talc, soda ash, and potash. It has been used worldwide from the Czech Republic to Canada, to China to the US.
Planning for the development of room and pillar mines operates in much the same way as other mining methods, and begins with establishing ownership of the mine. Then the geology of the mine must be analysed, as this will determine factors like the lifespan of the mine, the production requirements, and the cost to develop and maintain.
Next, mine layout is determined, considering factors like ventilation, electrical power, and haulage of the ore in cost analysis. Due to the non-homogeneous nature of mineral deposits typically mined by room and pillar, mine layout must be mapped very carefully. It is desirable to keep the size and shape of rooms and pillars consistent, but some mines have strayed from this formula due to lack of planning and deposit characteristics. Mine layout includes the size of rooms and pillars in the mines, but also includes factors like the number and type of entries, roof height, ventilation, and cut sequence.
Room and pillar mines are developed on a grid basis except where geological features such as faults require the regular pattern to be modified. The size of the pillars is determined by calculation. The load-bearing capacity of the material above and below the material being mined and the capacity of the mined material determines the pillar size.
Random mine layout makes ventilation planning difficult, and if the pillars are too small, there is the risk that they will fail. In coal mines, pillar failures are known as squeezes because the roof squeezes down, crushing the pillars. Once one pillar fails, the weight on the adjacent pillars increases, and the result is a chain reaction of pillar failures. Once started, such chain reactions can be extremely difficult to stop, even if they spread slowly. To prevent this from happening, the mine is divided into areas or panels. Pillars known as barrier pillars separate the panels. The barrier pillars are significantly larger than the "panel" pillars and are sized to allow them to support a significant part of the panel and prevent progressive collapse of the mine in the event of failure of the panel pillars.
Traditionally, the act of mining consists of three steps. First, the deposit is "undercut", where a slot is cut as deep as possible along the bottom of a section of ore. This undercut allows for a manageable pile of rock in later stages. The second step is the drilling and blasting of the section. This creates a pile of ore that is loaded and hauled out of the mine—the final step of the mining process. More modern room and pillar mines use a more "continuous" method, that uses machinery to simultaneously grind off rock and move it to the surface.
Other processes, such as backfill, where discarded tailings are unloaded into mined-out areas, can be used, but are not required. Retreat mining (below) is an example of a process like this.