A Major Infrastructure Project and the Formation of the UK's Largest Rotary Pile under Polymer Support Fluid-Paper

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The paper reports the use of polymer support fluid for large-diameter piles on London’s Northern Line Extension project at Battersea. The works included 74 piles, up to 2.4 m in diameter and over 60 m deep, alongside diaphragm walls constructed with bentonite. The largest pile required 270 m³ of support fluid, and 13,260 m³ of excavation was completed using polymer.<br /><br />A dedicated polymer plant and rigorous quality-control system were established to manage the fluid. Because local water hardness reduced polymer performance, the mixing water was treated to raise its pH. Polymer fluid was tested for viscosity, density, sand content and pH at preparation, after excavation and before concreting. Solids were allowed to settle within the pile bore, followed by cleaning and further testing before concrete placement. Returned fluid was rejuvenated for reuse. The fluid also remained in storage during a planned work suspension without significant loss of properties.<br /><br />Compared with bentonite, polymer required no soil-slurry separation plant and allowed faster fluid recovery, although in-hole settling required waiting time and excavation took about an hour longer in the observed comparison. Separate polymer operations also reduced reliance on the bentonite plant, which was serving the concurrent diaphragm-wall works. Thermal integrity testing confirmed satisfactory integrity for piles constructed with either fluid, and concrete displacement was comparable.<br /><br />The project demonstrated that polymer fluid can support major deep-pile construction with effective quality control. Benefits included a smaller plant footprint, reuse of the fluid throughout the works, no polymer-fluid disposal during construction, and lower liquid-waste disposal costs at project close.

Keywords

polymer support fluid

large-diameter piles

London Northern Line Extension

Battersea

diaphragm walls

bentonite

quality control

pile excavation

fluid reuse

thermal integrity testing