workers in  process; workers in  process;

Claridge's Basement Extension, London

Digging deep: Claridge’s five star basement extension

Claridge’s is a five-star hotel in the heart of London’s exclusive Mayfair district. The owners wanted to enhance the services and capacity offered to their guests, but needed more space in order to do it. The hotel’s location meant that extending at street level was not feasible, so an alternative solution was found: excavating under the hotel’s Art Deco wing.

Keeping Claridge’s open during basement construction

When the Maybourne Hotel Group proposed that their Claridge’s hotel extend in the basement underneath its Grade–II listed building, it was advised the hotel would have to close during the works. When it revisited the idea ten years later, Arup and McGee developed a methodology to excavate and construct a five-storey basement while Claridge’s remained fully operational.

This was a truly unique project as it required designing and building a deep basement beneath an 80-year old concrete raft. To add to the complexity, all materials going in and out of the site had to pass through a window opening, as any other method would involve transporting them through the hotel.

Project Summary


5,500 basement to be created

62existing building columns

25,000m3of material excavated

Proving it could be done

Our structural and geotechnical engineers, together with our advanced technology and research group, McGee and temporary works designers RKD, spent six months carrying out site trials, material tests and analysis to demonstrate that the concept was buildable.

Reinforced concrete columns provide support to the building above. Reinforced concrete columns provide support to the building above.
Five-storey high reinforced concrete columns were built to support the building above.

Pioneering solutions with tunnel design

The solution involved hand digging small tunnels under the existing ground-bearing raft slab. Circular shafts 1.8m in diameter were hand-dug up to 30m deep under each of the 62 existing building columns. Working in exceptionally tight spaces, the five-storey high reinforced concrete columns were built within the shafts, up to the underside of the existing raft, providing vertical support to the building above. To protect the hotel, real-time monitoring and the facility to jack ground settlements or heave was established at each column location.

Following the mining phase of construction the basement work is almost complete. The process is complemented by hand-excavated deep tunnels and shafts which make way for the distribution of building services.

Foundations up to 30m deep and 5m in diameter were dug by hand. Foundations up to 30m deep and 5m in diameter were dug by hand.
Foundations up to 30m deep and 5m in diameter were dug by hand.

A hotel for the 21st century

The additional 5,500m² of space will house a range of offerings including a spa, swimming pool, wine cellar, additional plant and back of house facilities. All of these will be developed in the Claridge's basement with no disturbance to guests, through our pioneering construction designs. 

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