ADMIRALTY
ARCH.

DELIVERING A COMPLEX BASEMENT BENEATH LONDON’S MOST ICONIC ARCHES.

CLIENT: PRIME INVESTORS

STATUS: COMPLETE

LOCATION: THE MALL

The client's vision looked to retain the history of the heritage building through careful restoration while enhancing its facilities with a double basement build.

PROJECT OVERVIEW.

To secure the Grade-I-listed building’s long-term future while gaining the most value from the project, two double storey basements were created on either side of the iconic arch. In doing so, we created an additional 2,900m2 of extra space, ready to be transformed into a ballroom and spa.

PROJECT HIGHLIGHTS AND KEY STATS.
3000m3 OF CONCRETE POURED
2,900m2 OF ADDITIONAL SPACE CREATED
2,000 LOADS OF EXCAVATION ARISINGS
150 LOW HEAD ROOM PILES INSTALLED
THE ADMIRALTY ARCH BASEMENT PROJECT WON THE STRUCTURAL ENGINEERING CATEGORY AT THE YEAR IN INFRASTRUCTURE AWARDS 2019.
KEY ACHIEVEMENTS.

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

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

Overcoming Logistics
The location of the Arch on The Mall meant traffic had to keep flowing during the construction of the new basement. Add to this the building’s ceremonial role, meaning 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.

THIS PROJECT EXEMPLIFIES OUR ABILITY TO OVERCOME COMPLEX CHALLENGES INHERENT IN LONDON CONSTRUCTION.

OUR COMMITMENT TO PRESERVING HERITAGE, MAXIMISING SPACE, AND MINIMISING DISRUPTION UNDERSCORES OUR DEDICATION TO DELIVERING HIGH-QUALITY SPECIALIST ENGINEERING PROJECTS IN CHALLENGING ENVIRONMENTS.
SEB FOSSEY
GROUP MANAGING DIRECTOR
KEY STAKEHOLDERS:

STRUCTURAL ENGINEER: WSP