Author: S. Fryer, M. Couchman and T. Eckhart (all BuroHappold Ltd)
2 July 2018
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S. Fryer, M. Couchman and T. Eckhart (all BuroHappold Ltd)
The OLE is supported by gantries of various types and configurations. In the case of the Great Eastern, the gantries date from the electrification of UK railways in the 1940s.
Initial structural assessment carried out had shown that existing gantries on the route were inadequate to carry increased loading from the upgraded OLE. However, a rigorous procedure incorporating detailed non-linear structural analysis was developed that eliminated some of the inherent conservatism in traditional codified approaches. Particular benefit was found in the case of the many types of slender structure where buckling was a governing factor. Using non-linear techniques, it was possible to demonstrate that families of structures were suitable for incorporation in the Crossrail (Elizabeth line) scheme.
This paper describes the approach that was used. The project is remarkable for significant programme and cost savings that were accomplished using sophisticated engineering analysis. It is also noteworthy from a sustainability point of view, as it allowed the existing infrastructure to be reused.
There is something special about megaprojects that brings out the best in engineering design and construction. It could be that the longer-term durations for the planning, design and build phases allow more measured and thoughtful decision making; it could be that the weight of public exposure and expectation creates an added incentive to succeed; it could be that the prestige of being part of the programme attracts the best teams in the best organisations; it could be that the extended schedule nurtures a team spirit and a collaborative way of working that is difficult to achieve in a typical shorter-term project.
All the articles from the July 2018 issue - a special issue on 'Structural engineering for the Elizabeth line'.
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.