20 Fenchurch Street

Location: London, UK

20 Fenchurch Street is a development which includes a new 36-storey skyscraper, nicknamed the Walkie Talkie. The previous building on the site had been constructed on under-reamed pile foundations with a single level of basement. The new building formation level is significantly deeper than the original,  and so the original under-reamed piled foundations were assessed to have little usable capacity. Piles for the new building had, where necessary, to be threaded between the existing pile under-reams; the new piles were designed such that they were entirely in the London Clay, making them considerably more economic and faster to install than if they had to penetrate into the deeper strata.

GCG worked as geotechnical sub-consultants to the structural engineers and jointly developed the new foundation scheme and carried out iterative analyses of the piled raft foundation; GCG later provided a full-time presence on site during the piling works. GCG also carried out assessments of retaining wall movements and their impact on neighbouring structures and infrastructure, working with the construction team to agree trigger levels of movement.