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An adit (from Latin ''aditus'', entrance) or stulm is a horizontal or nearly horizontal passage to an underground mine. Miners can use adits for access, drainage, ventilation, and extracting minerals at the lowest convenient level. Adits are also used to explore for mineral veins. Although most strongly associated with mining, the term ''adit'' is sometimes also used in the context of underground excavation for non-mining purposes; for example, to refer to smaller underground passageways excavated for underground metro systems, to provide pedestrian access to stations (pedestrian adits), and for access required during construction (construction adits).


Construction

Adits are driven into the side of a hill or mountain, and are often used when an ore body 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 the
lode In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fracture (or crack) in a rock formation or a vein of ore that is deposited or embedded between layers of rock. The current meaning (ore vein) dates from th ...
or 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 called drift 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

Access to a mine by adit has many advantages over the vertical access shafts used in shaft 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 of narrow-gauge tramway or cable car is also much safer and can move more people and ore than vertical elevators. In the past horses and pit ponies were used. In combination with shafts, adits form an important element in the ventilation 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

Most adits are designed to slope slightly upwards from the entrance so that water will flow freely out of the mine.Earl 1994, p.36. 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 term mine drainage tunnel is 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 the
water table The water table is the upper surface of the phreatic zone or zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with groundwater, which may be fresh, saline, or brackish, depending on the loc ...
will 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 the Milwr tunnel in North Wales, which is about long. Other examples are the Great County Adit in Cornwall, a -long network of adits that used to drain the whole Gwennap mining area, and the Sutro Tunnel at the
Comstock Lode The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada (then western Utah Territory), which was the first major discovery of silver ore in the U ...
in Virginia City,
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
. 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 copper mines in Cornwall and Devon because the ore-bearing veins are nearly vertical, thus acting as ingress channels for water.


Notable examples

* Great County Adit, a system of over of adits used for dewatering more than 100 mines in the Gwennap area of
Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...
in the 18th and early 19th centuries. *The Hollingwood Common Canal is a disused navigable coal mine adit which terminated at the Chesterfield Canal at Hollingwood, near
Staveley, Derbyshire Staveley is a town and civil parish in the Borough of Chesterfield, Derbyshire, England, along the banks of the River Rother, South Yorkshire, River Rother (5 miles) northeast of Chesterfield, Derbyshire, Chesterfield, (5 miles) west of Clowne, ...
. * Milwr tunnel, a drainage adit in
North Wales North Wales ( ) is a Regions of Wales, region of Wales, encompassing its northernmost areas. It borders mid Wales to the south, England to the east, and the Irish Sea to the north and west. The area is highly mountainous and rural, with Snowdon ...
. Started in 1897, it still discharges an average of of water per day from the disused Halkyn District United Mines. * The Snowy Mountains hydroelectric and irrigation scheme in the Australian Snowy 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 Adit in Tarnowskie 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 down the steps in one shaft, have a ride in a boat, and go up the stairs in another shaft. * Blue Hawk Mine near
Kelowna Kelowna ( ) is a city on Okanagan Lake in the Okanagan, Okanagan Valley in the British Columbia Interior, southern interior of British Columbia, Canada. It serves as the head office of the Regional District of Central Okanagan. The name Kelowna ...
,
British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...
, Canada. * NORCAT's Underground Centre (Fecunis Adit), in Onaping,
Ontario Ontario is the southernmost Provinces and territories of Canada, province of Canada. Located in Central Canada, Ontario is the Population of Canada by province and territory, country's most populous province. As of the 2021 Canadian census, it ...
, Canada, used for underground training and mining technology development. * Sutro Tunnel for drainage and exploitation of the
Comstock Lode The Comstock Lode is a lode of silver ore located under the eastern slope of Mount Davidson, a peak in the Virginia Range in Virginia City, Nevada (then western Utah Territory), which was the first major discovery of silver ore in the U ...
in
Nevada Nevada ( ; ) is a landlocked state in the Western United States. It borders Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the seventh-most extensive, th ...
. * Tiefer stollen in Schauinsland near
Freiburg Freiburg im Breisgau or simply Freiburg is the List of cities in Baden-Württemberg by population, fourth-largest city of the German state of Baden-Württemberg after Stuttgart, Mannheim and Karlsruhe. Its built-up area has a population of abou ...
.


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 mining is 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 the Worsley Navigable Levels in
Greater Manchester Greater Manchester is a ceremonial county in North West England. It borders Lancashire to the north, Derbyshire and West Yorkshire to the east, Cheshire to the south, and Merseyside to the west. Its largest settlement is the city of Manchester. ...
,
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
, the levels were intentionally flooded and coal was transported on canal boats. *" Sough" is a term mainly used in the lead mining areas of Derbyshire. The main purpose of a sough is to drain water from the mine.


See also

*
Glossary of coal mining terminology This is a partial glossary of coal mining terminology commonly used in the coalfields of the United Kingdom. Some words were in use throughout the coalfields, some are historic and some are local to the different British coalfields. A Adit :An ...
* Mine caps


References


Sources

* {{Authority control Underground mining Water management in mining