- station location
- maximum gradients for the trains using the tunnels
- minimum curve radius of the trains
- the location of obstructions such as tube lines, building foundations, sewers and other tunnels
The tunnel lining design is dependant on the method of construction.
- Precast concrete segments will be designed to be built in rings behind the TBMs.
- These segments will be made in a factory and transported to the tunnelling worksite for construction.
- Each ring is connected to the previous one built forming a long tunnel of similar cross section behind the TBM.
- The sprayed concrete lining is applied in layers to the excavated ground to form a robust lining.
- This method of lining is slower to construct but is more suited to irregular shaped tunnels and tunnel connections.
The tunnel lining is designed for a design life of no less than 120 years.
Computer software is used to analyse tunnel construction and predict the effects on the ground above. Ground treatment may then be designed to improve the ground and reduce the effects on the surface and overlying structures.
