The height and breadth of the motorway section across the existing SH16 causeway needed to be increased for a 100-year lifespan to cater for the increase in traffic and projected rise in sea levels due to climate change. The task was challenging as the soft marine muds that support the causeway required stabilisation, and there was a need to keep the road fully operational during the work to minimise disruption to traffic.
Instead of increasing the breadth and height for 100 years in one operation, Aurecon advised the client to use a staged process of increasing the dimension over time to minimise the risk of settlement and slope failures. First, the height was increased to allow for a 50-year predicted sea-level rise – with the remaining work to be re-evaluated in the future as part of scheduled 40-year pavement rehabilitation works. The staged engineering solution improved constructability, reduced the project duration, and saved the client over NZD $50 million.