Development over London Underground tunnels: No. 1 Grafton Street

Abstract

This paper describes a case history associated with the design of a building scheme at a site in Mayfair, London situated directly above the existing London Underground's Victoria Line tunnels. It confirms how this important constraint of the presence of the tunnels, influenced the design and how the railway protection measures were agreed and implemented. It explains the development of the feasibility scheme, the detailed design of a raft foundation solution, the retained façade scheme and the requirement to limit settlement, thus restricting the effect on the existing tunnels. It shows that predictions of heave due to demolition, and settlement due to construction, were assessed as realistic and compared favourably against actual monitoring results obtained during the works. The paper suggests ‘best practice' when achieving railway protection measures for building structure design and provides recommendations for future projects above existing tunnels.