An in-depth approach: Marine Piling for a major expansion of London City Airport-Paper

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The paper describes the design and installation of more than 1,000 marine piles supporting a new parallel taxiway and aircraft stands at London City Airport. Built over the former King George V Dock, the project required a 20-acre reinforced-concrete deck supported by piles installed from floating barges. Tight airport operating windows, nearby residents, potential unexploded ordnance (UXO), variable water levels and strict pile-position tolerances made construction particularly complex.<br /><br />Piles were formed using permanent steel casings and rotary boring under polymer support fluid, through dock sediments and into Thanet Sand or Chalk. During construction, 26 pile bores collapsed in the Thanet Sand. Investigation linked the failures to two interacting ground conditions: UXO-clearance work had disturbed the dock bed and punctured its previously undocumented puddle-clay liner, altering groundwater pressures; and geological faulting had sheared the Thanet Sand, reducing its dilatancy and ability to remain stable around a bore. The team initially stabilised collapsed bores by filling them with concrete and rebored them the following day. Longer casings and revised designs were also used where clearance excavations had disturbed the ground.<br /><br />Unexpectedly high and rapidly changing Chalk levels created additional design risks. The project responded by extending some piles into Chalk and commissioning a marine geophysics survey. Advanced 3D Chirp technology and AI-assisted processing mapped the Chalk surface and faulting in much greater detail than the widely spaced boreholes had provided.<br /><br />The project demonstrated that large-diameter rotary bored piling can be carried out from floating plant, but only with careful planning, skilled crews and purpose-designed procedures. The authors emphasise that early groundwater monitoring, comprehensive assessment of ground disturbance and geophysical surveys alongside intrusive investigations can improve ground models, reduce foundation risks and help avoid delays and redesign.

Keywords

marine piles

London City Airport

rotary bored piling

floating barges

Thanet Sand

Chalk geology

puddle-clay liner

unexploded ordnance

3D Chirp survey

groundwater monitoring