Te Ahu a Turanga – Manawatū Tararua HighwayReconnecting Manawatū-Whanganui and Hawkes Bay regions, Aotearoa New Zealand

Partnering with iwi delivered best outcomes

Partnering with iwi ensured the best solutions, for the best outcomes. It provided benefits to the project team, through upskilling around iwi priorities, which is being shared and adopted on other projects.

As project partners, iwi were also intrinsically involved during the construction of the new highway, with business and mentoring opportunities for local Māori and Iwi businesses. iwi were intrinsically involved in setting up the Legacy outcomes framework and Health and Wellbeing strategy for the project.

Unique low damage design for seismic location

A key challenge was designing six bridges in a high seismic location, including a 295 metre in-situ balanced cantilever bridge (88 metre main span) across the Manawatū River.

Conventional elastic or ductile design of the reinforced concrete substructure was determined to be not economically feasible, leading the Alliance to develop a low damage seismic solution. The superstructure is supported by seismic isolation lead rubber bearings, consisting of a core of lead surrounded by a rubber bearing, which change the period of the bridge, isolating it from the ground.

In a major earthquake, because the bridge is separated with isolation bearings, it doesn’t sustain the same damage as a conventional bridge. This ensures a reliable and resilient route for traffic including emergency services, while also avoiding the investment required for post-earthquake repair when compared with a conventionally designed bridge, which could be 10-20 per cent of the construction value.

Sliding design for shifting fault line

Another challenge presented by the high seismic location was designing a bridge which straddles a branch of the Wellington fault line. The fault line creeps 1-5 mm/year, and the bridge must withstand these ongoing shifts, maintaining stability.

It’s an unusual challenge and required an unconventional design. The Alliance’s solution entailed a single span bridge, supported by two large pad foundations which sit on walls either side of the river.

Digital technology a game-changer at every stage

Te Ahu a Turanga: Manawatū Tararua Highway project demonstrated the value of digital technology to achieve improved efficiency, time and cost savings during procurement and construction. Digital tools and 3D models for the entire project were used to co-ordinate and visualise designs across six offices, workstreams and with key stakeholders including NZTA.

Virtual Reality (VR) was embraced through all stages of the project for inductions, critical risk simulations and to enhance engagement with partners and stakeholders to deepen understanding of how key design elements integrate – for example, the complex interaction between bridges, earthworks, drainage and cultural expression design elements.

Digital tools enhanced the Alliance's one-team culture, while producing culturally appropriate designs, dashboard reporting, and minimised scope creep.

VR was also used to support constructability for structures, wetlands, barriers, and the SUP, which optimised designs for safe maintenance access and was critical to the fast-tracked consenting approvals process. The Alliance also provided iwi with GIS tools to map sites of significance.

The Alliance’s use of digital enhanced the one-team culture, and produced culturally appropriate and constructable designs, digital dashboard reporting, and developed an integrated risk-based TOC and programme that minimised scope creep. Digital adoption also proved pivotal in the tender stage, enabling NZTA and iwi to understand the Alliance’s thinking and see first-hand how the new highway will integrate into its environmental and cultural context.