Foundations for the Pinnacle Tower

The Pinnacle Tower in the City of London will be one of the tallest building in the UK when complete - 62 storeys high (290m), with a deep three-level basement that will compromise the deepest, largest foundations of their kind in the UK.

The Pinnacle Tower, London
The Pinnacle Tower, London

Challenge summary

The Pinnacle Tower is being constructed on a complex site, previously occupied by three buildings, leaving the ground riddled with existing piled foundations and basement structures which were obstructing any new works. Quantifying these obstructions at an early stage was therefore critical to keeping the project on time and budget for the client, Arab Investments Ltd.

Challenge solution

The engineer designers, Arup, carried out extensive research by searching archives, talking with old contractors and undertook intrusive investigation (coring and probing of existing foundations, geology and basement structures) on the site to find out more details about the old buildings.

Thinking Outside the Box

It was not possible to support the weight of such a huge tower using normal London foundation design and construction methods. The designers had to think out of the box and come up with an innovative solution to the problem. They decided to build the deepest and largest diameter piles in the UK, making use of the high capacity of the geology at deeper levels beneath the ground surface. Even by making the foundations so big, there were concerns that they might settle too much and cause the impressive tower to crack.

Base Grouting and Health & Safety

Pinnacle Tower foundations
Pinnacle Tower foundations

To avoid this, the foundations were 'base grouted', whereby grout was injected through pipes under pressure, to the base of the pile to increase the stiffness of the soil beneath the base of the pile and reduce settlement. The design and construction team also had to consider how to meet the technical and health and safety management challenges of piling through 3 levels of basement while controlling quality on site when the grout was pumped out under a column of concrete in excess of the length of an Olympic swimming pool.

This was achieved by developing a standardised scoring system to rate construction quality and a close working relationship between the foundation designers Arup, who monitored works on site throughout construction, and the foundation contractors, Bachy Soletanche.

2014 Update

The Pinnacle project is currently on hold subject to approval of a re-design.

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