Tunnel Segments are precast concrete pieces that form the tunnel lining, the tunnel’s structural wall.
Historical Note: While modern linings are predominantly precast concrete, materials such as cast iron (traditionally used for the London Underground) and steel liners have been used in the past. Concrete linings are favoured today for their smooth finish, durability, and inherent fire resistance.
They are manufactured under controlled factory conditions, ensuring high quality and precision.
The segments are assembled into rings as the tunnel boring machine (TBM) advances, providing immediate, robust, and watertight support to the excavated ground.
While they typically form circular rings, they can be cast to suit any tunnel shape.
