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Construction Processes
Mining Processes
Quarrying is a form of mining similar to open-pit mining, involving the extraction of useful natural stone from a man-made open pit called a quarry by cutting, digging, or blasting. Rock is either quarried as solid blocks or slabs, or crushed and broken. Minerals produced from quarries include coal, clay, gypsum, marble, gritstone, limestone, sand, and sandstone.[1] The industry is distinguished by dimension-stone and crushed-stone quarrying. The dimension-stone process involves the quarrying of solid blocks or slabs of stone used for decorative and ornamentation purposes. In the crushed-stone process, materials such as granite, limestone, sandstone, and basaltic rock are crushed for use in concrete aggregate or road stone for road construction.[2]
Limestone is just one of many types of natural stone quarried in man-made open pits.

Quarrying is an activity closely connected to the construction industry. Many quarries feature on-site processing plants that include ready-mix concrete plants and coating plants to make asphalt, bituminous road materials, cement- and lime-burning kilns, concrete block and pipe works, brick works, pottery works, and plaster and plaster board factories.[3]


[edit] Canada’s Quarrying Industry

The production of natural stone is an important industry in most Canadian provinces and is directly linked to construction. When a downturn occurs in construction, the demand for building materials produced from quarries will decrease.

The main types of stone quarried in Canada include limestone, granite, sandstone and marble. Limestone accounts for the majority of all stone produced—about 79 percent in terms of total volume in tonnage and 71 percent in value.[4] Ontario generates the most limestone in Canada followed in by Quebec, B.C., and Manitoba. Granite, marble, and sandstone are also produced but in smaller amounts.[5]

Most of the quarried limestone in Canada is crushed and used in the construction industry for concrete and aggregates. It is also used as a stabilizing base material in road construction, in fill and embankment reinforcement, railway ballast, in roofing granules, and in chips for stucco and terrazzo. Limestone can be pulverized and used as a filler or extender for cement. It is also a key component of agricultural fertilizer and an ingredient in chemical and pharmaceutical products.[6]

[edit] Process

Quarrying involves removing large amounts overburden such as soil or clay at the surface, or sinking a shaft or slope and then using the proper tools to extract stone from its bed by cutting, digging, or blasting. The method used to quarry stone depends on the stone’s composition, hardness, structure, cleavage, and other physical properties. The characteristics and placement of rock mass deposits is also an important consideration. For stone that is deposited in relatively accessible beds, hand tools such as drills, hammers, and wedges are employed. The demand for crushed rock such as limestone has actually led to the development of new kinds of quarrying techniques and quarrying is a less selective process than it used to be.
Remnants of an abandoned limestone quarry.

[edit] Explosives

The use of explosives capable of blasting away larger portions of hillside is a common method of quarrying today. The stone then gets split with the use of wedges or by the plug-and-feather method, or crushed by a heavy steel ball weighing several tons. Holes are drilled deep enough into the rock that it will break. The drilled holes are partially filled with explosives, which are then detonated.

Sometimes the holes are drilled along the outside of the rock block to be removed. Wedges, used in combination with explosives, are driven into a block of rock to split it into more manageable-sized pieces. Most quarries separate larger masses of rock first and then later divide the rock mass into smaller blocks of desired sizes. Sometimes the rock is stratified and then holes must be drilled at a right angle to the plane of separation. If a rock mass has no rift or stratification or the natural plane of separation is too far apart, then holes are drilled into the quarry face and wedges are driven into the rock to separate it. To prevent the stone from shattering, lighter gunpowder is preferred to fracture dimension-stone. In the production of crushed-stone, more powerful dynamite and explosives are used.

[edit] Compressed Air and Explosives

A new technique to emerge in granite quarries is the use of compressed air to separate layers of rock in conjunction with a small charge of dynamite. For example, granite has no natural rift so a hole is drilled down to the depth where the layer is to be split, creating a cavity in which a small amount of powder is exploded to produce a crack that runs parallel to the rock surface. A compressed air pipe is sealed into the opening to introduce increased pressure. Water under pressure may also be used with small amounts of gunpowder to achieve the same results.

[edit] Channeling

Another method of quarrying called channeling or broaching involves cutting long, narrow channels into the rock to free up the sides of large stone blocks. In this process special machines called channelers are used. Formerly steam-driven, these self-propelling machines today are powered by diesel or gasoline engines. They cut the stone with a cutting edge that traverses back and forth along the seam of the rock bed until a deep cut is made. The cut is deep enough to allow wedges to be inserted down into the rock until it is split. The cut in the stone is used to guide the fracture in the rock. The use of channeling is extensive in soft rock quarries such as those containing limestone, marble, and sandstone.[7]

[edit] Mining

Sometimes the stone bed to be quarried is too thin and removing the overburden on top is too expensive. In such situations the quarry is treated like a mine and the methods used to extract desired blocks of stone are similar to methods used in mining. For example, horizontal rock beds are cut near the top or the bottom of the bed. The face of the quarry is divided into blocks by saw cuts, channels, or rows of drilled holes. The blocks are then separated through wedging or blasting. As stoping moves forward, some of the rock is left behind as pillars to provide roof support. This approach is particularly common in European slate quarries where rock beds tend to dip down from a horizontal position. Similar to mining, the rock is worked by stopes that follow along the inclination of the rock bed.[8]

[edit] Equipment Used

[edit] References

  1. Quarrying. Knowledgerush 06-04-2009.
  2. Quarry and Quarrying. MSN Encarta. 06-04-2009.
  3. What do quarries produce? The Institute of Quarrying. 06-04-2009.
  4. Quarrying Industry. The Canadian Encyclopedia. 06-04-2009.
  5. Quarrying Industry. The Canadian Encyclopedia. 06-04-2009.
  6. Quarrying Industry. The Canadian Encyclopedia. 06-04-2009.
  7. Quarry and Quarrying. MSN Encarta. 06-04-2009.
  8. Quarrying. Classic Encyclopedia. 06-04-2009.