In civil engineering a shaft is an underground vertical or inclined passageway. Shafts are often entered through a

manhole A manhole (utility hole, maintenance hole, or sewer hole) is an opening to a confined space such as a shaft, utility vault, or large vessel. Manholes are often used as an access point for an underground public utility, allowing inspection, m ...

and closed by a

manhole cover A manhole cover or maintenance hole cover is a removable plate forming the lid over the opening of a manhole, an opening large enough for a person to pass through that is used as an access point for an underground vault or pipe. It is designed t ...

. They are constructed for a number of reasons including: * For the construction of a tunnel * For

ventilation Ventilation may refer to: * Ventilation (physiology), the movement of air between the environment and the lungs via inhalation and exhalation ** Mechanical ventilation, in medicine, using artificial methods to assist breathing *** Ventilator, a m ...

of a tunnel or underground structure, aka

ventilation shaft In subterranean civil engineering, ventilation shafts, also known as airshafts or vent shafts, are vertical passages used in mines and tunnels to move fresh air underground, and to remove stale air. In architecture, an airshaft is a small, ...

* As a drop shaft for a sewerage or water tunnel * For access to a tunnel or underground structure, also as an escape route

Construction

There are a number of methods for the construction of shafts, the most significant being: * The use of sheet piles, diaphragm walls or bored piles to construct a square or rectangular braced shaft * The use of segmental lining installed by

underpinning In construction or renovation, underpinning is the process of strengthening the foundation of an existing building or other structure. Underpinning may be necessary for a variety of reasons: * The original foundation isn't strong or stable enough. ...

or caisson sunk to form a circular shaft * Incremental excavation with a shotcrete circular or elliptical lining * Incremental excavation supported by shotcrete, rock bolts, cable anchors and steel sets or ribs Shafts can be sunk either dry or for methods such as the caisson method they can be sunk wet. Sinking a dry shaft means that any water that flows into the excavation is pumped out to leave no significant standing or flowing water in the base of the shaft. When wet sinking a shaft the shaft is allowed to flood and the muck is excavated out of the base of the shaft underwater using a grab on the end of a crane or similar excavation method. Because the shaft is flooded, the lining can not be constructed at the excavation level of the shaft so this method only suits methods where the lining is installed before shaft sinking (such as the use of sheet piles) or where the lining is sunk down with the shaft such as the caisson method. {{Authority control Civil engineering Tunnel construction