Concrete Arch with Seismic Design, Reinforced Earth® MSE Walls and Eleven Bridge Abutments

Completed in May 2020, the Transmission Gully Motorway Project (TGP) provides a new, 27-km-long, four-lane highway north of Wellington, New Zealand. This modern and safe main highway bypasses the coastal communities and space-limited choke points, which resulted in ever increasing traffic congestion on the existing SH1 highway.

The project was highly complex, with the alignment in places crossing steep, difficult, terrain and in other places crossing flood plains with deep, soft foundation soils. For much of its length the alignment is close to the active Ohariu fault. Twenty-five new bridges and large culverts are required over the length of the alignment. Many of the bridges are single span structures, with spans ranging from 22 m to 38 m.

The Wellington Gateway Partnership (WGP) and the New Zealand Government formed a Public Private Partnership (PPP) to deliver the Project. The WGP subcontracted the Design and Construction of the Project to a Joint Venture between CPB Contractors Pty Ltd and HEB Construction Ltd (a VINCI subsidiary), known as CPB HEB JV.

CPB HEB JV contracted Reinforced Earth Australia and New Zealand for the design and supply of materials for 10 bridge abutments using the Reinforced Earth® technique. Reinforced Earth considered in the design the proximity to the active Ohariu Fault with an effective magnitude of 7.

After the contract was signed, Reinforced Earth Ltd was awarded two further structures: abutments for a further single span bridge and a TechSpan® concrete arch system with extensive, associated Reinforced Earth® Walls.

The abutments for the eleven single span bridges required a total of circa 8,500 m2 of TerraClass® precast concrete facing panels, with the height of the walls varying between 1.6 m and 10.7 m. The TechSpan® precast concrete arch has a nominal span of 14 m with a height of 6.8 m. Associated Reinforced Earth® portal walls comprised 2,100 m2 of TerraPlus® precast concrete facing panels up to a maximum height of 16.8 m.

Construction of the first set of Reinforced Earth® Abutments began in July 2017, with all Reinforced Earth® structures substantially complete in October 2019.