The Southbank Place project comprises the redevelopment of the Shell headquarters in the Waterloo area of London with eight new buildings and refurbishment of the existing central tower. The site is bisected by London Underground’s Bakerloo Line tunnels that pass just below the existing basement. The Northern Line tunnels also pass beneath the north east corner of the site. The foundations for the tallest building comprise rotary bored piles up to 2100mm in diameter founded in the Thanet Sand layer, approximately 65m below ground level. A number of the piles were installed at a minimum offset of 1m from the extrados of the London Underground tunnels; the closest that piles have ever been installed next to live running tunnels in London. The paper describes the installation technique developed to minimise the impact of the pile installation on the tunnels, the state of the art numerical analyses used to predict the movements due to pile installation, the full scale instrumented field trial undertaken as part of the assurance procedure with London Underground’s infrastructure protection team and the observed tunnel movements following the installation of all the contract piles. The observed movements demonstrate the importance in the choice of soil model when analysing pile installation effects which include complicated stress paths, stress rotations and stress reversals. The work also demonstrated that with modern analytical tools and careful controls in place, piles can safely be installed at a 1m offset from live running tunnels in London Clay.
Subjects: None provided
Author: Stuart Hardy, Associate Director, Thomas Beales Ferguson, Geotechnical Engineer, Duncan Nicholson, Fellow, Jonathan Ly, Senior Design Manager and Laurent Olivier, Project Manager
Publisher: DFI, EFFC