The geometry of the basement was complex due to a number of protected trees around it’s perimeter. The client recognised at an early stage that this would make temporary works case during the excavation of the basement critical to the success of the project and contacted Foundation Piling for help.

Our early involvement assisted in developing a buildable solution for what would become the UK’s largest residential basement. This huge excavation required a 400m long retaining wall to accommodate a new full length swimming pool, accompanied by leisure facilities, a 130 seater cinema and a conference centre.

The ground consists of Claygate Beds, a cohesive soil with granular soil layers bearing water. A secant wall was used to seal the water bearing soils. The client had requested a single prop solution with for retained heights up to a depth of 13m.

Our design comprised 750mm diameter piles at 1050mm centres, designed to both retain the ground behind and provide a seal against groundwater ingress for ease of excavation. Our 27-tonne torque SR70 machine was used to construct piles with segmental casing used to maintain high tolerances on pile verticality. This ensured that all piles maintained interlock into the sealing strata.

In areas close to the existing buildings, wall deflections were a critical element of the design to prevent damage to the structures. Our design was validated with accurate measurement of the short-term and long-term deflections to ensure maximum quality control.

The scheme included difficult access elements working around the existing Leo Baeck House. The building’s façade was retained while a secant wall was built through the walls of the building. The building was then underpinned on piles constructed with restricted access equipment, and left suspended above the basement as it was excavated.

Foundation Piling continued to provide design support to the Main Contractor and their temporary propping provider post construction to ensure the success of follow on works.

The project has since featured in the New Civil Engineer.