Before revision: They are constructed for a number of reasons including: For the construction of a tunnel For ventilation of a tunnel or underground structure 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 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.
After revision: , aka ventilation shaftThey are constructed for a number of reasons including: For the construction of a tunnel For ventilation of a tunnel or underground structure 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 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.