Piling Adjacent to Rail Tunnels at King's Cross Central-PPT Presentation

PPT Presentation

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The King’s Cross Central development involved 11- and 12-storey office buildings (Plots S3 and S1) constructed above Network Rail’s Thameslink Canal Tunnels. Their structural designs required extensive piling close to the live tunnels, within designated exclusion zones.<br /><br />The project team designed and installed contiguous and bearing piles using continuous flight auger (CFA) and large-diameter auger (LDA) methods. Piles reached up to 56 m in length. Designs followed Eurocode 7 and London guidance for bored piles in London Clay, with settlement criteria set for serviceability. Ground investigations informed the designs, while unexpected conditions encountered at S3 were addressed collaboratively.<br /><br />A preliminary load test on a 38 m-long, 750 mm-diameter LDA pile at S3 validated the design and construction method. Measured settlements were lower than predicted, supporting a reduced model factor and an optimized design with shorter piles.<br /><br />Construction controls included installing contiguous piles in a hit-and-miss sequence, extending temporary casing to at least tunnel invert level, and checking pile verticality. Tunnel movements were monitored before, during and after piling using automated instruments. The tunnels settled by no more than 3.3 mm, broadly in line with predictions.<br /><br />The project was completed on time and to a high standard, protecting critical railway infrastructure while enabling development. The authors emphasize that comparable outcomes depend on thorough site investigation, suitable equipment and methods, careful planning and organization, and an experienced piling contractor.

Keywords

King’s Cross Central

office buildings

Network Rail tunnels

piling design

continuous flight auger

large-diameter auger

Eurocode 7

load test

tunnel settlement

London Clay