Controlling Ground Movements Due to Pile Installation Adjacent to London Underground Tunnels for the Southbank Place Project-Paper

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The Southbank Place redevelopment in London required deep, large-diameter rotary bored piles for a 36-storey residential tower above the Northern Line tunnels. Some piles, up to 2.1 m in diameter and founded about 65 m below ground, were installed just 1 m from the live tunnels—the closest such piling next to London Underground tunnels in London.<br /><br />A controlled installation method was developed to reduce risks including bore instability, bentonite migration toward the tunnels, and ground movement caused by stress changes. The method used permanent steel casing through the tunnel depth and avoided a second casing, which analysis indicated could increase tunnel movements. A full-scale instrumented trial, undertaken away from the tunnels, tested the method and compared predicted ground movements with measurements.<br /><br />Three-dimensional finite-element analyses used two London Clay soil models: BRICK and the Jardine model. Although both reproduced historical tunnel heave from basement excavation, they predicted substantially different movements during pile installation. Trial measurements were small and supported the BRICK predictions. The model better represented the stress rotations and reversals produced as the pile bore advanced and concrete was placed; the Jardine model did not automatically capture these effects and predicted larger movements.<br /><br />During installation of the contract piles, tunnel movements remained very small, with maximum vertical movement of about 1–1.5 mm. Results broadly agreed with the trial and BRICK analysis.<br /><br />The project demonstrated that piles can be installed safely 1 m from live London Underground tunnels when installation is carefully controlled, supported by full-scale trials, suitable numerical modelling, and close tunnel monitoring. It also highlighted the importance of selecting a soil model capable of representing the complex stress paths associated with pile installation.

Keywords

Southbank Place

London Underground tunnels

rotary bored piles

deep foundation

36-storey tower

London Clay

finite element analysis

pile installation

tunnel monitoring

instrumented trial