Northern Corridor Improvements

NCI Alliance

shutdown required


cut-in chambers completed


existing wastewater treatment ponds connected


works self-performed

Abergeldie delivered works as part of the larger Northern Corridor Improvement project for the NCI Alliance. The project connected two existing wastewater treatment ponds and diverted the pre-existing TS7 trunk main through a new route, allowing the demolition of the existing pipe bridge before constructing the new motorway onramp. Key to the success of this project was the collaborative coordination and management of isolations by Abergeldie and the Watercare Operations team.

Scope of works

Abergeldie self-performed 92% of the works. The works included:   

  • Pipe jacked tunnel construction. 
  • Shafts. 
  • Fabricated steel work. 
  • Live cutovers. 
  • Maintenance holes.
  • RRCJ pipework. 
  • Multiple motorway crossings using specialist tunnelling machines. 
  • Installation of new trunk sewer main via open trench excavation. This included having to cut into the existing trunk sewer and build new chambers at the cut-in locations.

Innovative solutions

Throughout the project, the team adeptly tackled complex challenges using innovative approaches. The project team addressed unexpected ground conditions with the sunk caisson technique and modified the Tunnel Boring Machine. Abergeldie also adopted clever solutions like pipe diversion and precast maintenance hole channel units to manage flow effectively, ensuring uninterrupted operations at the Rosedale Wastewater Treatment Plant and trunk sewer network without any uncontrolled discharges. 

Sustainable construction practices

Waste reduction was prioritised through the utilisation of recycled construction materials and sourcing from local suppliers, minimising the need for extensive fuel consumption. The project team implemented collaborative carpooling to further decrease emissions from transportation. Additional initiatives involved the use of eco-friendly oils and fluids in machinery, along with the implementation of demand-controlled/self-starting power-generating plants to further curtail fuel consumption throughout the project. 

Engaging local

Abergeldie collaborated with Māori and Pacifica Trade Training (MPTT) to recruit and develop staff through an apprenticeship partnership scheme. Further, we supported our existing staff in upskilling and gaining additional qualifications throughout the project. 

Efficient trunk sewer construction

The three cut-in chambers had to be completed with live flows and no over-pumping. Due to the large flow volume in the trunk sewer, there was no room for error. Consequently, the construction team developed a special methodology to build the chambers around the pipe. 

This involved temporary pipe supports for existing services, with benching formed and poured at the surface. The benches were then lowered into place after removing the trunk sewer from the chamber. This methodology allowed for live flows throughout the process, requiring only a single pump station shutdown for an eight-hour period. The work was completed without any incidents. 

Essential infrastructure for the new highway

The completed works for the Northern Corridor Improvements were integral to the larger highway construction of a new motorway between the Northern Motorway and the Upper Highway, enhancing connectivity to Auckland Airport, West Auckland, Manukau, and Hamilton in New Zealand.