Developers Axa Real Estate and Lipton Rogers have announced that work on 22 Bishopsgate – formerly known as The Pinnacle – is to restart with the existing above ground structure to be demolished but the foundations retained.
Bachy Soletanche completed the foundations work to a design by Arup on the site in 2009 but work on the tower halted soon after due to the financial crisis.
Axa bought the site and partially completed building in February this year for a reported £300M.
The developers have said that the new 278m tall, 62 floor tower will use the foundations and basements from the previous design in order to minimise disruption.
According to Axa, the new design by Karen Cook of PLP Architects will fill an obvious gap at the centre of the city’s cluster of tall buildings and the design reflect changes in tall buidings since The Pinnacle gained planning consent in 2007.
Developers have planned to build a a public viewing gallery at the top of the building, which will feature dedicated lifts free to the public, and have a two-storey public restaurant and bar at the side.
The foundations installed for the Pinnacle were designed to support loads reaching up to 70MN and the piles are driven through through London clay and into more unstable Thanet sands.
GE reported in 2010 that the Bishopsgate site covered the footprint of three previous buildings and was cluttered with piles, including 1.5m diameter bored piles and 4.5m underream bells of the former Standard Chartered Bank building.
At some points 20m of reinforced concrete had to be bored through, which ruled out minipiles and caissons. There was also question mark over the performance of underreeam bells in Thanet sands, base grouted piles were the preferred option.
Speaking at the time of the work, Arup geotechnical director Dinesh Patel said: “It sounds outrageous: coring existing [underream] piles and then base grouting into Thanet sands - who would do that?”
Base grouted piles in Thanet sand had only been used twice before in the UK - at Canary Wharf, where Thanets are found at depths of only 25m, and more recently at the Moorhouse development in the City of London.
Early contractor involvement with Bachy Soletanche to develop a design for the 2.4m diameter, 63m deep piles and reuse of some existing piles secured the project at GE Award at the 2010 event in the Project with a Geotechnical Value of Over £1M category.