The shaft buildings serve as emergency exits. The metro tunnel shafts are located at intervals of approximately 600 metres and extend to ground level. They serve as an emergency exit, a smoke vent, a pressure equalisation system and a ventilation system. The middle of the shaft contains a fire-compartmented escape route staircase. Vertical shafts are located aboveground, in public street and park areas.
At the start of the shaft construction, the worksite area is fenced off and ground excavation and grading excavation begin. The actual shaft excavation takes place from below, within the tunnel, such that the blast rock falls into the underground rail tunnel and is hauled out along the tunnel.
The shaft buildings are technical spaces that are roughly the size of small detached houses, with a full height of approx. 3 metres and a floor area of approx. 100 m2. The shaft’s surrounding environment is landscaped according to the yard design plan for that shaft. The surface material for the shafts of the Ruoholahti–Matinkylä metro section is steel mesh sheets.
As part of phase two of the West Metro project, technical shafts for seven metro stations and two shafts for the Sammalvuori depot are being built. The shafts are built as part of the rail line construction contract.