Austroads Bridge Conference, 2025, Brisbane
The New Bridgewater Bridge (NBB) Project is Tasmania’s largest ever transport infrastructure project. The project is a critical link in Tasmania’s transport network and forms part of the Australian Government’s National Land Transport Network. The NBB project involves construction of a fourlane, 1.28-kilometre-long bridge over the River Derwent with new interchanges at Granton and Bridgewater, a shared path for cyclists and pedestrians, and a navigation clearance consistent with the Bowen Bridge, all aimed at improving traffic flow and connectivity. The NBB replaces the existing steel-truss vertical lift bridge, which was completed in 1946. The new bridge comprises a total of 21 bridge piers and 2 abutment piers with each span varying from 44 m to 64 m in length. The total width of the bridge deck ranges from 25m to 30m and will accommodate four traffic lanes and a shared use path. A precast single-cell box girder structure supporting each carriageway is supported on a 2.8m diameter single pier connected to a 2.5m diameter concrete bored pile socketed into very variable weathered rock except for the abutment piers where 2.1 m diameter piles are adopted. The centre to centre spacing of the piles within each individual pier is approximately 14 m. The length of foundation piles below the top of the pile varies from 12.5 m to 86.5 m with the latter likely to be the deepest mono bored pile in the Southern Hemisphere. This paper commences with a brief description of geological conditions along new bridge alignment and then discusses the basis of design. The paper moves further to provide an overview of the foundation systems adopted for the bridge, and to discuss design approaches, key geotechnical issues and challenges encountered in design and construction of production piles; subsequently presents an overview of the use of Osterberg cell testing to verify axial capacity; and finally presents some technical insights for future design and construction of similar deep foundations as conclusions.
