Case History
The Pinnacle Tower – Geotechnical Challenges
Dinesh Patel, Sarah Glover, Jonathan Chew, Jenny Austin
Ove Arup and Partners, London, United Kingdom
The Pinnacle Tower is one of a cluster of towers being constructed in the heart of the City of London. When complete it will be 62 Storeys high – taller than any other building in the UK. The design and construction of the tallest building in the UK, on a central London site occupied by 3 existing buildings presented special challenges. The approach the design and construction team took to these challenges earned them the best geotechnical project over £1M at the recent GE awards.
The new development
The new building is to be 62 storeys with a 3 level basement (Figure 1) occupying a retail and commercial office space of about 1.4M sq ft. Demolition of the previous 10 storey buildings to ground level started in mid 2007. Pile construction started in July 2008 from the ground level slab, over an existing three level basement which occupied much of the site. Piling is now complete, demolition and basement excavation continues as with pile cap construction progresses. The new substructure and superstructure is planned for completion in 2012.
Figure 1: The Pinnacle Tower (copyright KPF web site)
In London, tall buildings are typically less than 200m high and have traditionally been founded on large diameter bored piles (including under-reamed piles) in London Clay typically 25 to 35m deep. Canary Wharf Tower at 235m, is founded characteristically on 25m deep base grouted bored piles in the Thanet Sand, supporting maximum loads of about 30MN. The Pinnacle, has typical column loads up to 45MN with some extreme loads of up to 70MN and cannot be supported on any currently known piling system drilling into just London Clay. For this reason the only sensible solution was to found into the Thanet Sand, which at this site is about 63m below street level. The very high loads resulted in piles having diameters up to 2.4m.
Download ISSMGE Bulletin – Volume 4 Issue 1 (pp. 9-24)
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