The new stormwater pipeline involved the underground pipe jacking construction of stormwater pipes with an internal diameter of 2.55 m, one of the largest diameters to be constructed and jacked in New Zealand, with a total installed length of approximately 855 m. The original contract was for 570 m of pipeline however, due to the success of the first stages of the project, and the relationship between McConnell Dowell and the Auckland City Council, McConnell Dowell was granted an extension for a further 280 m of pipeline.
The works took place around residential areas of Auckland, where noise and vibration was limited, and the need for minimal settlement was paramount.
The project included a 300 m long pipe jack, which was achieved through competent sandstone material. A Herrenknecht Roadheader was used for the tunnel
excavation.
The tunnels were constructed from reinforced concrete jacking pipes with an internal diameter of 2550 mm. Each jacking pipe was approximately 2.5 m long and manufactured by local suppliers.
The geology was weathered but competent sandstone. In certain areas soft clay bands were encountered which minimised the roadheaders ability to cut. In these soft clays hand excavation was necessary.