A benchmark case history: design and full-scale performance of recorded-length monopiles for the award-winning New Bridgewater Bridge

The award-winning New Bridgewater Bridge (NBB) Project represents Tasmania’s largest-ever transport infrastructure undertaking. Its success hinges on the geotechnical design of large-diameter monopiles supporting 21 bridge piers and two abutment piers across the River Derwent. Ranging from 2.1 to 2.45 meters in diameter and socketed into variable rock, one pile reached 91.5 meters, potentially making it the deepest mono-bored pile in the Southern Hemisphere. The challenging geological environment, featuring estuarine muds and diverse rocks, demanded rigorous assessments of scour and seismic hazards, including liquefaction and lateral spreading. Advanced iterative design processes were utilized. Osterberg cell (O-cell) testing provided pivotal design validation, confirming that mobilized shaft skin friction and end bearing resistance exceeded assumptions. Surveys showed over 82% of the piles exhibited settlements matching predictions within ±1–4 mm under dead loads. This robust empirical validation proves the accuracy of the employed methodologies, offering significant insights for future deep foundation projects.