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

Building capacity for Claridge’s by building down

When the Maybourne Hotel Group proposed that their Claridge’s hotel extends into the basement underneath the Grade-II listed building, it was advised the hotel would have to close during the works. When the idea was revisited 10 years later, Arup and McGee developed a process to excavate and construct a five-storey basement while Claridge’s remained fully operational. Our structural engineers, together with McGee and temporary works designers RKD, spent six months carrying out site trials, material tests and analysis to demonstrate that the concept was buildable.

This truly unique project required the designing and building of a deep basement beneath an 80-year-old concrete raft. Adding 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. 

The additional 5,500m² of space houses a range of facilities, including a spa, swimming pool. wine cellar, and additional  back of house facilities. All of these were developed in the Claridge’s basement with no disturbance to guests, through Arup’s pioneering construction designs. 

CGI of five-storey high reinforced concrete columns for Claridges basement extension
Five-storey high reinforced concrete columns were built to support the building above.

Tunnel vision for innovative tunnel design 

Our structural and geotechnical engineers’ 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 existing raft’s underside, 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. 

After securing the weight of the hotel onto the 100-year raft with the new foundation caissons and columns, the 5 levels of basement were excavated in a top-down manner, complemented by hand-excavated deep tunnels and shafts which made way for the distribution of building services. 

Claridge's basement extension. Credit Nick Carter
Foundations up to 30m deep and 5m in diameter were dug by hand.