Client name: NZ Transport Agency

Duration: March 2013 – December 2016

Location: Auckland, New Zealand 

Safety, innovative engineering and reduction of construction costs were priorities for the Causeway Alliance – AECOM, Coffey, CPB Contractors, Fulton Hogan, Jacobs and the Transport Agency.

Ensuring a causeway running through deep soft soils has minimal impact on marine reserve

The SH16 Causeway Upgrade is a key part of the Western Ring Route, one of the Government's seven Roads of National Significance. Once completed, the Western Ring Route will provide a strategic alternative to SH1, central Auckland and the Auckland Harbour Bridge.

The Causeway Upgrade Project connects with the St Lukes Upgrade, Waterview Connection and Te Atatu Interchange Improvement projects, which will link the Southwestern (SH20) and Northwestern (SH16) motorways and provide greater capacity for this alternative route around the city.

The project had a number of challenges, including the deep, very soft soils the 4.8km stretch of SH16 is constructed on. Left untreated, on-going repairs would be required and further settlement and flooding would occur.

The project also ran through the Motu Manawa Pollen Island Marine Reserve and there were measures in place to ensure that all project works had minimal impact on the reserve and surrounding environment.

Staged cost effective solution to prevent flooding and mitigate settlement risk 

The Causeway Alliance raised the motorway 1.5 metres to prevent flooding, and widened it to provide additional capacity in both directions.

The cycleway alongside the motorway was also raised, widened and upgraded.

The design incorporated a cost effective solution of wick drains, preloading and the use of lightweight pumice sand to mitigate both total and differential settlement risk.

By optimising the final embankment width and adopting an asymmetric widening option, the Causeway Alliance significantly reduced the overall footprint of the project.

The work was completed in stages so that disruption to the community, the environment and to traffic was kept to a minimum.

Innovative ground improvement solutions 

The upgrade was completed in December 2016, before the Waterview Tunnels open in early 2017.

The Causeway Alliance has provided value for money with innovative solutions for ground improvements.

The team has reduced the need for potential future reclamation and safeguarded against coastal erosion and storm tides while maintaining full access to traffic and cyclists.

This innovation will ultimately mean a more efficient network system, as well as improved public transport connections and cycleway access.

Client testimonial

"Coffey has provided innovative and cost effective ground improvement solutions, while minimising environmental impacts. Their knowledge of technical issues associated with the Causeway Upgrade Project have given me confidence that our engineering risk will be reduced and that we will stay on target for our completion date."

Mark Evans
Alliance Project Manager
Causeway Alliance
SH16 Causeway Upgrade Project, Auckland