Kings Gate House

The basement spans across the entire footprint of the site and accommodates the UKPN substation. Our scope of works included sub and superstructure works, excavation, groundwork and the installation of associated drainage and services. Throughout the project we utilised 4D modelling to help with the planning and sequencing. We were working within a tight footprint and took care not to impact on the immediate environment which was fully operational throughout the works. This was coupled with the challenges of implementing top-down methodology and therefore required the use of Heidi, our specialist telescopic excavator.

We were ultimately responsible for the concrete work for the substructure and superstructure. A complete 4D computer model was developed by our in-house design team to coordinate enabling work for the deep excavation, basement construction work to ensure the construction sequence, temporary work installation and construction of sub and superstructure are well planned. The major challenge was the correct sequencing when working in areas of conventional excavation and top-down construction.

Additionally, we carried out enabling works to the existing basement box, including removal of existing foundations, probing and removal of obstructions along the secant pile wall prior to the piling. Our enabling works also involved the probing of new pile locations, the formation of the perimeter capping beams, temporary works with the bulk excavation, construction of the basement slabs, tower crane base construction and the installation of lightning protection.

The west building comprised two areas both requiring traditional open sky excavation. However, because of site logistics and the requirement to hand over the central section of the basement to UKPN early, this area was constructed in advance using a contiguous piled wall in conjunction with steel sheet piles, steel waling and two levels of props. The east block was constructed using a top-down method to allow early installation of the isolation bearings under the floating ground floor slab and construction challenge was forming the basement through an existing structure, while maintaining stability of surrounding assets including Westminster City Hall and other party wall agreements.