THE SCHEME
Located on Charing Cross Road, Ilona Rose House will deliver outstanding new shops and restaurants, along with high-quality office space for the creative industries. The building will play host to the film and creative industries in Soho for many years to come. The site will be complimented by rooftop gardens, public art and transformed streetscape along Manette Street and through to a new walkway into Greek Street.
DESIGN AND PLANNING
Bachy Soletanche was responsible for the pile design and worked closely with Tier Consult, who were responsible for fixing the location of the piles. The total loading of the structure did not change but there were a few changes to the distribution of the loads, which called for alterations to the pile sizes. The project required a mixture of different techniques which included secant piled retaining walls, load bearing piles (included geothermal loops), plunge columns and restricted access piles in low headroom locations.
Ground conditions are formed by London Clay to 33m but there is a 1m to 1.5m thick sand layer at that level, which overlays another 10m of soft London Clay before the Thanet Sand is encountered at around 44m below ground level.
PILING OPERATIONS
The secant wall was formed of an outer wall around the perimeter of the site, along with an unusual internal secant wall, located on the Charing Cross Road side of the site. The reason for the additional wall was due to the close proximity of the Northern Line tube tunnels, which run along the site boundary and are approximately 33m below the ground level. The secant wall piles in this part of the site are 17m long, where as the remaining piles have been bored to a depth of 23.5m. In total over 400 piles were used to form the wall, which had a total linear length of 235m and will form a four-storey basement.
In addition to the wall the team constructed 121 bearing piles, which ranged between 600mm and 900mm in diameter. The piles were bored to an average depth of 52.5m and had geothermal loops installed to help cool and heat the building.
The site is adjacent to Greek Street, where it wraps around a Grade II listed building and a façade, which will be restored as part of the overall project. In this zone the team had to use the restricted access method due to the structural steel supporting the façade.
Bachy Soletanche constructed 34 piles which were 450mm in diameter and were bored up to 25m in depth. The rig had to be lifted over the secant wall and into the working zone through space just 3m in height. Finally, the team installed nine 750m diameter temporary piles which included plunge columns. The columns were then used to construct a working platform from which was used for the basement excavation works.
LOGISTICAL CHALLENGE
Getting plant, concrete and reinforcement cages onto site was logisctically challenging due to the restricted access, which minimised the length of deliveries to 15m, and partly drove the three-part cage design for the bearing piles. Westminster City Council and Camden Council had to provide special dispensation to track the rig onto site from Charing Cross Road.
