ADMIRALTY

ARCH.

Structural Engineering Solutions: To address the challenges posed by the soil and the underground tunnel, precise structural engineering was crucial. Thicker foundations and a heavier raft were employed to control tunnel movement and reduce tension on the piles. Collaborating with third-party experts, optimal thickness, concrete amount, and reinforcement ratios were determined to balance cost-effectiveness and space maximisation.

Innovative Construction Methods: A secant box construction method was utilised on both sides of the arch, with the ground floor slab suspended on plunge columns. A top-down basement construction technique was employed, utilising traditional moling hole operations to minimise disruption.

Overcoming Logistics: The location of the Arch on The Mall also meant that traffic had to keep flowing during the construction of the new basement. Adding to this, the building’s ceremonial role meant that should a procession need to pass through, all signs of construction would have to be completely removed at extremely short notice.

Preservation of Historic Elements: Internal cores were sunk in the north and south blocks, allowing for the extension of the Grade I listed staircase to match the new external B2 level. Additionally, a tunnel was constructed to link the cores, showcasing meticulous attention to preserving historic features.