Author: G. Kumar (TfL Engineering, ex-AECOM) and D.Sharples (AECOM)
2 July 2018
G. Kumar (TfL Engineering, ex-AECOM) and D.Sharples (AECOM)
Farringdon Elizabeth line station comprises two platform tunnels, each 245m long, between new ticket halls over 300m apart. Each ticket hall has been designed to accommodate future oversite developments.
This paper discusses the structural engineering challenges encountered during design and construction of the two ticket halls on constrained sites surrounded by existing transport infrastructure, utilities and historic buildings.
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 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.