Overcoming location challenges when building on top of London Underground
Installing structural steelwork directly above rail tunnels has several challenges that need to be addressed during the planning stage. Close collaboration is needed to plan the foundation structure, improve buildability and minimise acoustic vibrations.
Elland Steel Structures has successfully completed many contracts in busy locations with limited access, including Central House in London. This is one of the reasons why Elland Steel was awarded the contract for the Kings Cross Bridge office building.
This tight construction site was directly on top of the London underground, which meant complex enabling works.
As part of the structural package, we were asked to install 3 steel staircases and the floor and roof decking. This is in addition to the 230 tonnes of steel that we fabricated for the basement, upper and lower ground floors, levels 1 & 2 and the roof.
Ramboll assisted with complicated enabling works
Our collaboration with Ramboll and Murphy group helped improve buildability, particularly as Ramboll provided engineering expertise for the complex enabling works.
This started in the Underground line, when the ground floor supporting structure was established. The office block’s retained basement slab would actually be the tunnel soffit of the Metropolitan Line (of London underground) and the Moorgate Line (part of Network Rail).
The steelwork was designed to be lightweight so the imposed load on the foundations would not impact the infrastructure below. As well as this, the frame was designed to use part of the existing frame.
Minimising disruption
The site is surrounded by one of the busiest cross-sections in the capital. This meant that we needed to carefully plan ‘just-in-time’ deliveries. Due to the nature of the active rail-lines below, anti-vibration bearing springs were utilised in the structure and foundations. This minimised the transfer of sound and vibration from the trains below.
Close collaboration was vital to the success of the project
We asked for feedback at various stages of the project. Overall, we gained an excellent net promoter score of 90 for this project for our collaboration. We were particularly praised for our director-led approach to project management.
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