Shaft (civil engineering)

In civil engineering a shaft is an underground vertical or inclined passageway. Shafts are often entered through a manhole and closed by a manhole cover. They are constructed for a number of reasons including:
Construction.
There are a number of methods for the construction of shafts, the most significant being:
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.