21 Moorfields is an air-rights commercial development directly above Moorgate Underground (LUL) station, London. Constraints include six railway lines at LUL station level, two Crossrail tunnels below ground, station services, the new Crossrail ticket hall and a major sewer. Existing 7-storey buildings are demolished to the station roof level, followed by the construction of a 17-storey office building that will bridge 55m over Moorgate Station. This development will enrich the urban habitat around this transportation hub.
Key technical challenges
The station stays fully operational during the construction. This requirement is met through the existing roof being modified to act as a crash-deck and laydown area for the piling and construction above.
The entire superstructure bridges 55m across the station.
An externally expressed dia-grid spans across the east elevation, contributing to the architectural identity of the building. Six mega-arches which support the internal floors are integrated into trading and office floorplates, and minimise the number of columns to six on a typical floor.
Limited locations for foundations
The Mega-Arches are supported on fifteen large diameter bored piles base grouted into the underlying Thanet sands and cased within the station. Piles are installed from a steel grillage which supports 200T BG40 piling loads and is constructed from the existing station roof. Piles are located within back of house areas in the station, avoiding underground services and assets.
Construction staging, movements and crane logistics
RBG developed a clear construction methodology into the permanent structural and architectural design. Deep launching trusses integrated into the Level 01 internal spaces are used to construct the arches and are pre-set to reduce movement zones. Crane support gantries are coordinated with the permanent design and plant installation.
£550M TBC (shell and core)
55mm bridge building over Moorgate Station
Robert Bird Group Services:
Structural and Civil Engineering Design and Construction Engineering support.