Definition - What does Access Shaft mean?
An access shaft is a pit or wall sunk from the surface for the purpose of furnishing ventilation to the tunnel. This ventilation opening which extends from ground level to the underground tunnel, can also provide physical access to a given section of the tunnel for inspection or continuing construction.
Trenchlesspedia explains Access Shaft
Access shafts provide access from the surface, to the level of a tunnel or bore. These shafts provide workers access which allows for equipment and other materials, as well as air flow, to enter the work area below the surface. They're most often drilled from the surface downward, to one side of the the tunnel's designed pathway. Construction may also require an access shaft through the top of the design pathway to allow machinery to be introduced.