Room and pillar or pillar and stall is a variant of breast stoping. It 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. [1] 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. [2] 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, recovery and profits can be low. [1] Room and pillar mining was one of the earliest methods used, [3] although with significantly more manpower.
The room and pillar system is used in mining coal, gypsum, [4] iron, [5] limestone, [6] and uranium [7] ores, particularly when found as manto or blanket deposits, stone and aggregates, talc, soda ash, and potash. [8] It has been used worldwide from the Czech Republic [2] to China [9] to the US. [4]
Planning for the development of room and pillar mines operates in much the same way as other mining methods, [10] and begins with establishing ownership of the mine. Following this, 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. [10]
Next, mine layout should be determined, as factors like ventilation, electrical power, and haulage of the ore must be considered [4] [10] 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. [10] It is desirable to keep the size and shape of rooms and pillars consistent, but some mines strayed from this formula due to lack of planning and deposit characteristics. [4] 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. [10]
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. [10]
Random mine layout makes ventilation planning difficult, and if the pillars are too small, there is the risk of pillar failure. 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. [11] To prevent this from happening, the mine is divided up into areas or panels. [10] 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. [10]
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. [10] 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. [12]
Other processes, such as backfill, where discarded tailings are unloaded into mined-out areas, [9] can be used, but are not required. Retreat mining (below) is an example of a process like this.
Retreat mining is often the final stage of room and pillar mining. Once a deposit has been exhausted using this method, the pillars that were left behind initially are removed, or "pulled", retreating back towards the mine's entrance. After the pillars are removed, the roof (or back) is allowed to collapse behind the mining area. Pillar removal must occur in a very precise order to reduce the risks to workers, owing to the high stresses placed on the remaining pillars by the abutment stresses of the caving ground.
Retreat mining is a particularly dangerous form of mining. According to the Mine Safety and Health Administration (MSHA), pillar recovery mining has been historically responsible for 25% of American coal mining deaths caused by failures of the roof or walls, even though it represents only 10% of the coal mining industry. [13] Retreat mining cannot be used in areas where subsidence is not acceptable, reducing profitability. [13]
Sometimes retreat mining is not used and the underground space is repurposed as climate controlled storage or office space instead. [14] [15]
Many room and pillar mines have been abandoned for as long as 100 years. [5] This drastically increases the risk of subsidence unless properly maintained, [5] however, maintenance does not often occur. [7]
Room and pillar mining is one of the oldest mining methods. Early room and pillar mines were developed more or less at random, with pillar sizes determined empirically and headings driven in whichever direction was convenient. [16]
Room and pillar mining was in use throughout Europe as early as the 13th century, [17] and the United States since the late 18th century. It is still in use throughout the US, [12] but has slowed or stopped entirely in parts of Europe. [17]
Coal mining in the United States has nearly always operated with a room and pillar layout, although originally operated with significantly more manpower. [10]
Room and pillar mining of gypsum was used in Iowa beginning in 1892, and was phased out of use in 1927 due to low recovery and development of technologies that made surface mining more practical, safe, and cost effective. [4] More recently, the United States Gypsum Sperry mine, near Mediapolis, Iowa, opened in 1961. This room-and-pillar mine, 620 feet (190 m) below the surface, has square pillars 37 feet (11 m) on a side separating rooms of the same width in a gypsum bed about 10 feet (3.0 m) thick. [18]
Many salt mines use room and pillar layouts. The Sifto salt mine in Goderich, Ontario, the largest in the world, was opened in 1959. It taps a salt bed 30 metres (98 ft) thick 533 metres (1,749 ft) below the surface, mostly under Lake Huron. [19] The Cargill salt mine 1,700 feet (520 m) below the surface, mostly under Lake Erie at Cleveland, Ohio is similar. [20]
Modern room and pillar mines can be few and far between. This is due to many factors, including the dangers to miners associated with subsidence, increasing use of other methods with more mechanization, and the decreasing cost of surface mining.[ citation needed ]
Room and pillar mining is not particularly dependent on the depth of the deposit. At particularly deep depths, room and pillar mining can be more cost effective compared to strip mining due to the fact that significantly less overburden needs to be removed. [9] This means that today, room and pillar mining is mostly used for high grade, but small, deep deposits.[ citation needed ]
Due to a recovery rate as low as 40% in some cases, [4] room and pillar mining cannot compete in terms of profitability with many modern, more mechanized types of mining such as longwall or surface mining.[ citation needed ]
Abandoned mines have a tendency to collapse. In remote areas, collapses can be dangerous to wildlife, [21] but subsidence of abandoned mines can be hazardous to infrastructure above and nearby. [5] [17] Significant amount of coal is left on the pillars as roof support.
Mining is the extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agricultural processes, or feasibly created artificially in a laboratory or factory. Ores recovered by mining include metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. The ore must be a rock or mineral that contains valuable constituent, can be extracted or mined and sold for profit. Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water.
Underground hard-rock mining refers to various underground mining techniques used to excavate "hard" minerals, usually those containing metals, such as ore containing gold, silver, iron, copper, zinc, nickel, tin, and lead. It also involves the same techniques used to excavate ores of gems, such as diamonds and rubies. Soft-rock mining refers to the excavation of softer minerals, such as salt, coal, and oil sands.
Coal mining is the process of extracting coal from the ground or from a mine. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from iron ore and for cement production. In the United Kingdom and South Africa, a coal mine and its structures are a colliery, a coal mine is called a "pit", and above-ground mining structures are referred to as a "pit head". In Australia, "colliery" generally refers to an underground coal mine.
Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique that extracts rock or minerals from the earth using a pit, sometimes known as a borrow pit.
In mining, tailings or tails are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different from overburden, which is the waste rock or other material that overlies an ore or mineral body and is displaced during mining without being processed.
Wapno is a village in Wągrowiec County, in the Greater Poland Voivodeship, close to the border with Żnin County. Wapno is Polish for lime and reflects the large gypsum deposits in the area, which can be processed to produce lime. There are also large deposits of rock salt that were mined extensively beginning in the nineteenth century.
Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice. The section of rock that is being mined, known as the longwall panel, is typically 3–4 km (1.9–2.5 mi) long, but can be up to 7.5 km (4.7 mi) long and 250–400 m (820–1,310 ft) wide.
Surface mining, including strip mining, open-pit mining and mountaintop removal mining, is a broad category of mining in which soil and rock overlying the mineral deposit are removed, in contrast to underground mining, in which the overlying rock is left in place, and the mineral is removed through shafts or tunnels.
Drift mining is either the mining of an ore deposit by underground methods, or the working of coal seams accessed by adits driven into the surface outcrop of the coal bed. A drift mine is an underground mine in which the entry or access is above water level and generally on the slope of a hill, driven horizontally into the ore seam.
A cave-in is a collapse of a geologic formation, mine or structure which may occur during mining, tunneling, or steep-walled excavation such as trenching. Geologic structures prone to spontaneous cave-ins include alvar, tsingy and other limestone formations, but can also include lava tubes and a variety of other subsurface rock formations. Glacier caves and other ice formations are very prone to collapse from exposure to warm temperatures or running water.
Underground soft-rock mining is a group of underground mining techniques used to extract coal, oil shale, potash, and other minerals or geological materials from sedimentary ("soft") rocks. Because deposits in sedimentary rocks are commonly layered and relatively less hard, the mining methods used differ from those used to mine deposits in igneous or metamorphic rocks. Underground mining techniques also differ greatly from those of surface mining.
Retreat mining is the removal of pillars in the underground mining technique known as room and pillar mining.
A coal mine bump is a seismic jolt occurring within an underground mine due to the explosive collapse of one or more support pillars.
The following outline is provided as an overview of and topical guide to mining:
Stoping is the process of extracting the desired ore or other mineral from an underground mine, leaving behind an open space known as a stope. Stoping is used when the country rock is sufficiently strong not to collapse into the stope, although in most cases artificial support is also provided.
A Pinge or Binge ("binger") is the name given in German-speaking Europe to a wedge-, ditch- or funnel-shaped depression in the terrain caused by mining activity. This depression or sink-hole is frequently caused by the collapse of old underground mine workings that are close to the Earth's surface. Unlike natural landforms, a Pinge is a direct result of human activity. The term has no direct equivalent in English, but may be translated as "mining sink-hole", "mine slump" or, in some cases, as "glory hole".
The Coalbrook mining disaster is the worst mining accident in the history of South Africa. The disaster occurred in the Coalbrook coal mine of Clydesdale Colliery on 21 January 1960 at around 19:00 when approximately 900 pillars caved in, almost 180 metres (590 ft) underground. The mine is situated in the Northern Free State, 21 kilometres (13 mi) south west of Vereeniging. About 1,000 miners were in the mine at the time and 437 died after being trapped, while the rest escaped through an incline shaft. The miners were suffocated by methane gas and crushed to death by rockfall.
Dawson Valley Colliery is a heritage-listed former coal mine at Morgan Street and The Esplanade, Baralaba, Shire of Banana, Queensland, Australia. It was built from 1921 onwards. It is also known as Baralaba Coal Mine. It was added to the Queensland Heritage Register on 18 September 2009.
In the mid-19th century, Colorado Springs was a center of mining industry activity. Coal was mined in 50 mines in the area and towns, now annexed to Colorado Springs, were established to support residents of the coal mining industry.
A flash is a body of water that forms where the land below it has subsided. Whilst these are mostly found in areas where mining has taken place, some can occur naturally. Collectively they are known as Flashes
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