Dinesh Patel, Sarah Glover, Jonathan Chew and Jenny Austin, Arup. This paper was first published in GE’s November 2015 edition.
This paper describes the design and construction of deep base grouted bored piles for The Pinnacle (figure 1a) – a planned 290m high skyscraper in the City of London. Pile loads from this structure were expected to be up to 45MN, and this meant that the piles had to extend into the Thanet Sand stratum, 63m below ground level. The decision to have single piles per column also meant that, not only were the piles the deepest, but also the largest ever built in the City, at 2.4m in diameter.
This paper also presents the results of an instrumented base grouted pile load test to approximately 25MN. This paper was initially presented at the EFFC’s 2010 conference in London but work on The Pinnacle halted after the foundations and the substructure up to ground level were completed sometime after presentation of this paper.
The paper has been updated for GE as work on the site has recently restarted and some of the existing foundations will be used to support the new 22 Bishopsgate development (figure 1b), which is being undertaken by developers Axa Real Estate and Lipton Rogers. In addition to the restart of work on site, there has also been a rise in the use of base grouted piles in London in the last 12 months and the assessments made in this paper in regard to design and construction are relevant to future projects.