Adit

For the ADIT, seeAdvanced Diploma in International Taxation.

For the Indonesian animated series, seeAdit Sopo Jarwo.

Gated entrance of an abandoned adit nearMedford, Oregon,United States

Anadit(from Latinaditus,entrance)orstulm is a horizontal or nearly horizontal passage to anunderground mine. Miners can use adits for access, drainage,ventilation, and extracting minerals at the lowest convenient level.Adits are also used to explore formineral veins.Although most strongly associated with mining, the termaditis sometimes also used in the context of underground excavation for non-mining purposes; for example, to refer to smaller underground passageways excavated for undergroundmetro systems,to provide pedestrian access to stations (pedestrian adits), and for access required during construction (construction adits).

Construction

Queen Louiseadit, Zabrze, Poland

Adits are driven into the side of a hill or mountain, and are often used when anorebody is located inside the mountain but above the adjacent valley floor or coastal plain. In cases where the mineral vein outcrops at the surface, the adit may follow thelodeor vein until it is worked out, in which case the adit is rarely straight. The use of adits for the extraction of ore is generally calleddrift mining.

Adits can only be driven into a mine where the local topography permits. There will be no opportunity to drive an adit to a mine situated on a large flat plain, for instance. Also if the ground is weak, the cost of shoring up a long adit may outweigh its possible advantages.

Access and ventilation

Horse adit in the abandoned lead mine,Nenthead,County Durham, UK

Access to a mine by adit has many advantages over the vertical access shafts used inshaft mining.Less energy is required to transport miners and heavy equipment into and out of the mine. It is also much easier to bring ore or coal out of the mine. Horizontal travel by means ofnarrow gauge tramwayorcable caris also much safer and can move more people and ore than vertical elevators. In the past horses andpit ponieswere used.

In combination with shafts, adits form an important element in theventilation of a mine:in simple terms, cool air will enter through an adit, be warmed by the higher temperature underground and will naturally exhaust from vertical shafts, some of which are sunk specifically for this purpose.

Drainage

Two Brothers Adit, a small surviving mine entrance at the site ofEylesbarrow mine,Dartmoor,Devon

Most adits are designed to slope slightly upwards from the entrance so that water will flow freely out of the mine.Mines that have adits can be at least partly drained of water by gravity alone or power-assisted gravity. The depth to which a mine can be drained by gravity alone is defined by the deepest open adit which is known as the "drainage adit".The termmine drainage tunnelis also common, at least in the United States. Workings above this level (known as "above adit" ) will remain unflooded as long as the adit does not become blocked. All mine workings below both the drainage adit ( "below adit" ) and thewater tablewill flood unless mechanical means are used for drainage. Until the invention of the steam engine this was the main restriction on deep mining. Adits are useful for deeper mines. Water only needs to be raised to the drainage adit rather than to the surface.

Because of the great reduction in ongoing costs that a drainage adit can provide, they have sometimes been driven for great distances for this purpose. One example is theMilwr tunnelin North Wales, which is about ten miles (16 km) long. Other examples are theGreat County Aditin Cornwall, a 40-mile (64 km)-long network of adits that used to drain the wholeGwennapmining area, and the 3.9 miles (6.3 km)Sutro Tunnelat theComstock LodeinVirginia City,Nevada.A side benefit of driving such extensive adits is that previously unknown ore-bodies can be discovered, helping finance the enormous cost.

Adits were used in Cornwall before 1500, and were important to the tin and coppermines in Cornwall and Devonbecause the ore-bearing veins are nearly vertical, thus acting as ingress channels for water.

Notable examples

• Great County Adit,a system of over 40 miles (65 km) of adits used for dewatering more than 100 mines in theGwennaparea ofCornwallin the 18th and early 19th centuries.
• TheHollingwood Common Canalis a disusednavigablecoal mine adit which terminated at theChesterfield CanalatHollingwood,nearStaveley, Derbyshire.
• Milwr tunnel,a 10-mile long (16 km) drainage adit inNorth Wales.Started in 1897, it still discharges an average of 87 million litres (23 million US gallons) of water per day from the disused Halkyn District United Mines.
• TheSnowy Mountains hydroelectric and irrigation schemein the AustralianSnowy Mountains,created during its construction. The adits are very large and used to access the central point from which the hydro tunnels were constructed.
• Black Trout AditinTarnowskie Góry,Poland. Part of a former silver mine, the adit was used for removing water from the mine. It still carries water from old galleries to the nearest river. A part of it is open for tourists, who go 20 metres (66 ft) down the steps in one shaft, have a ride in a boat, and go up the stairs in another shaft.
• Blue Hawk MinenearKelowna,British Columbia,Canada.
• NORCAT's Underground Centre (Fecunis Adit), inOnaping,Ontario,Canada, used for underground training and mining technology development.
• Sutro Tunnelfor drainage and exploitation of theComstock LodeinNevada.

Similar terms

• A "drift" is a more general term for any near-horizontal underground passage in a mine. Unlike an adit, a drift need not break out to the surface.Drift miningis the use of drifts to extract ore - in this case the drifts follow the vein.
• A "level" is a horizontal passage that branches off from a shaft and is used for access to the parts of the mine where the ore is being removed. In mines where the lodes have significant vertical extent there can be many numbered levels, one below the other. They can be connected by short vertical shafts known as "winzes".A level that reaches the surface, on a hillside or in a valley, for instance, is called an" adit level ". In theWorsley Navigable LevelsinGreater Manchester,England,the levels were intentionally flooded and coal was transported on canal boats.
• "Sough"is a term mainly used in thelead mining areas of Derbyshire.The main purpose of a sough is to drain water from the mine.

See also

• Glossary of coal mining terminology
• Mine caps

Sources

• Earl, Bryan (1994).Cornish Mining: The Techniques of Metal Mining in the West of England, Past and Present(2nd ed.). St Austell: Cornish Hillside Publications.ISBN0-9519419-3-3.