Threaded Rotary Bored Piles at Paddington New Yard-Paper

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The paper describes SolThread, a modified rotary bored pile developed by Bachy Soletanche to improve pile capacity while reducing materials and spoil. After drilling a conventional 750 mm bore, a specialist tool cuts a helical thread into the shaft wall, enlarging the effective geotechnical diameter to 900 mm and mechanically interlocking the pile with the surrounding clay. Remote CCTV inspection and checks of collected spoil were used for quality control.<br /><br />The technique was first used at full scale on the Paddington New Yard project in London Clay. Preliminary static load tests compared threaded piles with conventional straight-shaft piles. Results supported increasing the design adhesion factor from 0.5 to 0.8, corresponding to a 40% increase in shaft capacity. A threaded pile of comparable capacity could therefore be shorter: on the project, pile length fell from 21 m to 15.5 m, while pile volume decreased by about 15%. The estimated carbon reduction was 10%.<br /><br />Reduced concrete and spoil also meant fewer truck movements, with potential benefits for site safety, local traffic and air quality. The threading operation’s additional time was offset by the shorter initial excavation, so overall construction time was reported as neutral. A limitation is that parts of the pile— including the bottom section—cannot be threaded and must be accounted for in design.<br /><br />Successful implementation depended on load testing, clear technical communication, client support for innovation, and a proportionate inspection regime. The project demonstrated that SolThread can provide a practical alternative to conventional bored piles, with potential for use on other projects and in larger diameters.

Keywords

SolThread

rotary bored pile

helical thread

pile capacity

London Clay

Paddington New Yard

static load tests

design adhesion factor

carbon reduction

construction efficiency