NZ Geotechnical Society (NZGS) 22nd Symposium 2025 Auckland
State Highway 25A (SH25A) between Kōpū and Hikuai, Coromandel Peninsula, suffered significant damage from a series of major storm events in January 2023. Cumulative storm damage caused a landslide to occur, resulting in the total loss of a section of SH25A measuring over 100m in length and severing the link.
A 124-metre multiple span bridge replacing the road was selected by NZTA as the safest to construct and most resilient option, with the shortest and most reliable timeframe for reconnecting Coromandel communities. Upon selection of the bridge repair option, contractors McConnell Dowell and Fulton Hogan in a joint venture, with support from Tonkin + Taylor and Beca, were selected to design and construct the bridge solution in June 2023. The bridge was constructed and SH25A open in less than 6 months from project award, and less than 12 months from the date when the damage occurred. A typical bridge of the type delivered would normally take 18 to 24 months to design and construct.
This paper covers the geotechnical challenges of the project, which included large scale slope failures, variable geology, and the fast-track design process, which was carried out in parallel with procurement and construction. The design and construction of the slope stabilisation works are described, including a cement-stabilised shear key, fill buttress embankment, soil nails, and horizontal drains. The bridge foundations are also discussed, describing pile and rock socket design, construction observations, and pile integrity testing.
