Crossrail project: machine-driven tunnels on the Elizabeth line, London

Summary

The 42 km of tunnels constructed using soft-ground pressure-balance tunnel-boring machines for London’s new Elizabeth line were completed over a 3 year period. A single lining design solution was developed for all tunnels using a fully gasketed, steel-fibre-reinforced, concrete segmental lining suitable for use in all potential ground conditions anticipated along the alignment. The £14·8 billion Crossrail project faced many challenges, including dealing with significant quantities of different excavated material while minimising the environmental impact from transportation and disposal, minimising settlement effects and dealing with multiple tunnel-boring machine launches and receptions. This paper addresses how the issues were tackled and comments on the tunnel-boring machine design and the approach taken for survey control. Outline figures are also provided for the tunnelling rates. Finally, some conclusions and recommendations are made based on the observations and lessons learnt during the project.