Shaft mining or shaft sinking is the action of excavating a mine shaft from the top down, where there is initially no access to the bottom. Shallow shafts, typically sunk for civil engineering projects, differ greatly in execution method from deep shafts, typically sunk for mining projects. Shaft sinking is one of the most difficult of all mining development methods: restricted space, gravity, groundwater and specialized procedures make the task quite formidable. Shafts may be sunk by conventional drill and blast or mechanised means. Historically, mine shaft sinking has been among the most dangerous of all the mining occupations and the preserve of mining contractors called sinkers. Today shaft sinking contractors are concentrated in Canada, Germany, China and South Africa. The modern shaft sinking industry is gradually shifting further towards greater mechanisation. Recent innovations in the form of full-face shaft boring (akin to a vertical tunnel boring machine) have shown promise but the use of this method is, as of 2019, not widespread.
Mine shafts Mine shafts are vertical or near-vertical tunnels, which are "sunk" as a means of accessing an underground ore body, during the development of an underground mine. The shape (in plan view), dimensions and depth of mine shafts vary greatly in response to the specific needs of the mine they are part of and the geology they are sunk through. For example, in North and South America, smaller shafts are designed to be rectangular in plan view with timber supports. Larger shafts are round in plan and are concrete lined. Mine shafts may be used for a variety of purposes, including as a means of escape in the event of an emergency underground and allowing for the movement of:
People Materials Mine services (such as compressed air, water, backfill, power, communications and fuel) Ventilation air Broken rock (in the form of payable ore, or non payable waste) Or any combination of the above When the top of the excavation is the ground surface, it is referred to as a shaft; when the top of the excavation is underground, it is called a winze or a sub-shaft. Small shafts may be excavated upwards from within an existing mine as long as there is access at the bottom, in which case they are called raises. A shaft may be either vertical or inclined (between 80 and 90 degrees to the horizontal), although most modern mine shafts are vertical. If access exists at the bottom of the proposed shaft, and ground conditions allow, then raise boring may be used to excavate the shaft from the bottom up; such shafts are called borehole shafts. Following the Hartley Colliery disaster where the single shaft at the mine became blocked, the United Kingdom made single shaft mines illegal in 1862, establishing the practice that all underground mines must have "a second means of egress". Many other global mining jurisdictions have adopted this rule and shafts are therefore often found in pairs (although there are multiple alternative methods of providing a second means of egress). Currently, the deepest continuous single-lift mine shaft in the world is the main shaft at South Deep Mine in South Africa, owned by Gold Fields Limited, which has a depth of 2991 meters. Along with its twin ventilation shafts, it took ten years to sink and equip.
Parts of a mine shaft
The most visible feature of a traditionally-built mine shaft is the headframe (or winding tower, poppet head or pit head) which stands above the shaft. Depending on the type of hoist (or winder) used, the top of the headframe will either house a hoist motor or a sheave wheel (with the hoist motor mounted on the ground). The headframe will also typically contain bins for storing ore being transferred to the processing facility. At ground level beneath and around the headframe is the Shaft Collar (also called the Bank or Deck), which provides the foundation necessary to support the weight of the headframe and provides a means for workers, materials and services to enter and exit the shaft. Collars are usually massive reinforced concrete structures with more than one level. If the shaft is used for mine ventilation, a plenum space or casing is incorporated into the collar to ensure the proper flow of air into and out of the mine. Beneath the collar the part of the shaft which continues into the ground is called the shaft barrel. At locations where the shaft barrel meets horizontal workings there is a shaft station (or inset) which allows men, materials and services to enter and exit the shaft. From the station tunnels (drifts, galleries or levels) extend towards the ore body, sometimes for many kilometers. The lowest shaft station is most often the point where rock leaves the mine levels and is transferred to the shaft, if so a loading pocket is excavated on one side of the shaft at this location to allow transfer facilities to be built. Beneath the lowest shaft station the shaft continues on for some distance; this area is referred to as the shaft bottom. A tunnel called a ramp typically connects the bottom of the shaft with the rest of the mine. This ramp often contains the mine's water handling facility, called the sump, as water will naturally flow to the lowest point in the mine.
Shaft lining
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