Author: T. Worsfold (Arup), M. Bryant (Canary Wharf Group) and J. Crack (Canary Wharf Group)
2 July 2018
First published: 2 July 2018
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T. Worsfold (Arup), M. Bryant (Canary Wharf Group) and J. Crack (Canary Wharf Group)
The new Elizabeth line station at Custom House was a unique opportunity for design and construction. It is the only above-ground station on the central section of the line and will welcome millions of visitors to London’s largest conference centre, ExCeL, as well as providing vital connections for the Borough of Newham. A joint team from Crossrail Ltd, Atkins, Arup, Allies & Morrison, and Laing O'Rourke collaborated to develop the striking station design, creating a beacon for both the Elizabeth line and the local community. Faced with many constraints, a ‘kit of parts’ strategy was developed for Custom House’s construction, including prefabricated and standardised components. This approach – where much of the station was built off site – minimised workon site, drove down programme times and costs, and reduced the impact on the local community. The approach also led to Custom House’s excellent health and safety record – one of the best of any Elizabeth line station to date.
The new Elizabeth line station at Tottenham Court Road, delivered by the Crossrail programme, has been an exercise in interface management as well as a feat of engineering. This paper describes the design carried out by the Arup Atkins Joint Venture (AAJV) under contract C134, principally of the Western Ticket Hall box. Nestled in Soho, this was developed within a dense urban grid and the constraints of a residential oversite development above. The team worked closely with London Underground Ltd's engineers at the Eastern Entrance, which was delivered as part of London Underground’s own station upgrade works. The tunnel for the eastbound Elizabeth line passes through the Western Ticket Hall box, which also provided construction access for the sprayed concrete-lined platform and concourse tunnels. Access dates to the site meant that there was insufficient time to complete construction of the box before the arrival of the tunnel boring machine (TBM). Consequently, the need to complete the excavation became critical and the team adopted a bottom-up construction sequence for one of the deepest open shafts ever excavated in central London. The box, formed of elements of diaphragm walls and raft, was constructed before the TBM arrived, and the remaining internal elements completed afterwards.
The Elizabeth line, due to open in December 2018, crosses London from west to east. The Crossrail project to construct the Elizabeth line has seen 21km of twin-bored tunnels constructed under central London, with eight new stations built on this section. The damage assessment and monitoring carried out comprised a significant element of work in terms of the resources involved, both human and financial. The background to this work was the experience from a number of tunnelling projects in London, probably most significantly that from the London Underground Jubilee line extension. While all assets along the alignment were subject to the same process, the impact of the works around the stations and shafts was calculated to be greater than along the bored tunnels, and the extent of instrumentation and monitoring was correspondingly higher. Both automated and manual methods were used, with instrumentation installed and readily visible on many buildings in these areas throughout the duration of the works. This paper looks at the damage assessment and monitoring of buildings around the stations, focusing in particular on the new station at Tottenham Court Road. It also provides an overview of the two very different tunnel construction methods used on the project – the so-called tunnel boring machine (TBM) and sprayed concrete lining (SCL) methods – and describes how these lead to the ground movement that is the principal source of potential damage to the buildings. Finally, the paper considers briefly some of the lessons learned and how these might be applied to future urban tunnelling projects.