Qualified pile load testing campaigns as a key aspect for the sustainable design of piled foundations for infrastructure projects-Paper

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The study presents a full-scale pile-testing campaign to support the sustainable, technically and economically optimized design of foundations for Hamburg’s A26 motorway bridge and elevated road. Challenging ground conditions, including thick organic soils, mean the project requires more than 1,500 large bored piles, many with enlarged bases.<br /><br />Twenty-eight test piles were built at four locations, varying one geometric or construction parameter at a time. The campaign examined pile diameter and length, base-widening geometry, and fully cased versus bentonite-suspension-supported construction. Static and dynamic axial tests were conducted, alongside extensive instrumentation, including vibrating-wire gauges and high-resolution fibre-optic sensors. Ultrasound and mechanical scanning, low-strain integrity testing, and thermal integrity testing were used to assess borehole geometry and pile quality.<br /><br />Testing showed that piles constructed with suspension support mobilized sand shaft friction comparable to fully cased piles; no systematic reduction was observed. Average shaft friction in the underlying sands was consistent with established empirical guidance. Shaft resistance was generally mobilized at relatively small settlements, while load transfer and creep in the soft organic layers require further consideration.<br /><br />Measured base pressures beneath the pile shaft were consistent with, or exceeded, guidance values for dense soils. Pressures beneath the enlarged annular base were substantially lower—often less than half those beneath the shaft. Consequently, roughly quadrupling the base area produced only about twice the base resistance in the conditions tested.<br /><br />Fibre-optic and conventional measurements showed good agreement, while continuous fibre-optic monitoring provided additional insight into load transfer, pile stiffness, and measurement plausibility. Overall, the campaign demonstrates how targeted load testing and improved instrumentation can refine foundation design, validate construction methods, and help reduce resource use and carbon impacts through better-informed pile sizing and performance assumptions.

Keywords

pile testing

foundation design

bored piles

Hamburg A26 motorway

shaft friction

base resistance

fibre-optic sensors

load transfer

organic soils

sustainable construction