Tunnel Segments FAQ

For our Tunnel Segments FAQ below are some questions that we are asked about Tunnel Segments on a regular basis.

Concrete moulds can be made to build almost anything out of concrete. The mould only needs to withstand the pressure of the concrete and it has to be shaped to contain the form you want.

There are currently 364 tunnels in the UK. The definition of a tunnel,  an underground passageway with no defined minimum length, though it may be considered at least twice as long as wide.

Tunnels in the UK are normally used for road networks, rail and waterways or aquaducts for people to travel through by foot or car but tunnels can also be used to route power or telecommunication cables or for wildlife to cross motorways.

Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions,

The ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation.

The final use and shape of the tunnel and appropriate risk management.

  • There are three basic types of tunnel construction in common use:
    Cut and cover tunnels, constructed in a shallow trench and covered over.
  • Bored tunnels, constructed in situ, without removing the ground above. They are usually of circular or horseshoe cross-section.
  • Immersed tube tunnels, sunk into a body of water and sit on, or buried just under, its bed.

Herrenknecht AG is a German manufacturer of tunnel boring machines of all sizes. Herrenknecht,  headquartered in Allmannsweier near Schwanau; the worlds market leader for heavy tunnel boring machines.

Roughly two-thirds of the 3,300 employees work at the company headquarters and roughly 300 work at three different locations in China.

Concrete formwork is essentially the frame or mould that holds wet concrete in place while it sets (or cures) fully. There are two main types of formwork – temporary and permanent.
Temporary formwork known as a reusable formwork, removed from around the concrete once set. Generally made from timber, steel, plywood or plastic.

Permanent formwork, a formwork that stays in place and never removed, an excellent example of this; Insulated Concrete Forms (ICFs). ICFs, made from a foam material (EPS – expanded polystyrene) contains a “hollow” in the middle into which concrete pours.

The combination of the foam and the concrete provides excellent thermal insulation to the building.

In early days manual shield tunnelling, was used as a way to protect labourers who performed the digging. The shield would protect workers and inches forward, and workers would progressively replace the shield with pre-built sections of tunnel wall.

The shield divides the workface into overlapping portions, so each worker could excavate. The same method used to build the London Underground.

The tunnel lining is the wall of the tunnel. It usually consists of precast concrete segments which form rings can cast suit any shape.

Cast iron linings, traditionally used in building the London Underground tunnels, while steel liners sometimes used for lining soft ground tunnels. Concrete linings provide a smooth surface and are fire resistant.

A concrete shaft, a shaft filled with concrete that helps to support a bridge or used in conjunction with tunnel panels to provide additional strength and durability.

The longest road tunnel in the UK is the A3 Hindhead Tunnel at 1.2 miles, which is between London and Portsmouth.

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