Geotechnical Design of Non-Conventional Bridge Abutments at the Hakao Gully in Tauranga, New Zealand

The Takitimu North Link (TNL) Stage 1 project delivers 6.8 km of new expressway: connection between State Highway 2 (west of Te Puna) to State Highway 29 (Takitimu Drive) and upgrade to the connecting stretch of State Highway 29 into Tauranga. The project is part of the government’s New Zealand Upgrade Programme (NZUP).

The Minden Gully Bridges are a set of three separate structures designed and constructed for this project, comprising of mainline, on-ramp and off-ramps bridges, all located within the same 25-40 m high, steeply sloped Hakao gully. The bridge abutments were formed as piers, connected to the ground behind with settlement slabs bearing on reinforced soil slopes. The geology of the site was found to be highly variable between the east and west sides of the gully, as well as some variation from north to south. As such, various refinements and sub-layering were completed as part of the geotechnical design to adequately capture site soil conditions. The complex geology and topography of the site, together with the selected bridge abutment arrangements, called for specific geotechnical design for each bridge, including achieving compatibility between each geotechnical element and soil-structure interaction for the design of shear pile ground improvement.