2430 x 2430 px | 41,1 x 41,1 cm | 16,2 x 16,2 inches | 150dpi
Data acquisizione:
13 dicembre 2002
Ubicazione:
50m underground between Stratford and Kings Cross, London, UK
Altre informazioni:
Questa immagine potrebbe avere delle imperfezioni perché è storica o di reportage.
Technical advances in Tunnel Boring Machine (TBMs), concrete segments and waterproof gaskets have allowed tunnelling to take place in tunnels with increasingly higher ground water pressures. This is important because many future tunnels will be constructed in increasingly less favourable geological conditions. Design, construction and erection of segmental pre-cast concrete linings are crucial steps for building a tunnel with an expected life of 100 years or more. As a TBM excavates its passage through the ground, the tunnel behind is lined with reinforced concrete segments. This lining is made of watertight segments forming a complete ring and creating a tube in the bored tunnel and, following erection of each ring, a special grout is injected between the excavated ground and the lining. There is no risk of a ground collapse or flooding, because the segments are put into position inside the watertight TBM. This means that the groundwater level does not have to be lowered and either the TBM or the concrete lining always provides support for the newly excavated tunnel. Earth Pressure Balance Machines (EPBMs) are tunnel boring machines specially designed for operation in soft ground conditions, particularly those containing water under pressure. EPBMs are utilized in the construction of rail tunnels, metropolitan subway systems, highway tunnels and other projects where the tunnel will be constructed either partly or completely in soft soil beneath the water table. Loose sedimentary deposits with large boulders and a high water table will challenge ordinary TBMs, but not EPBMs because they have an articulated shield that is sealed against the pressure of water inflows. EPBMs control the stability of the tunnel face and subsidence of the ground surface by adjusting the pressure inside the cutterhead chamber to achieve a balance with the pressure in front of the cutterhead.
