The trench, which will be excavated to a depth of 30m, will be where the 85m-long TBM will be assembled before beginning work excavation of the tunnels next year. Preparatory works and environmental controls have already been put in place to facilitate the start of construction including the provision of alternative open space, realignment and rehabilitation of parts of Oakley Creek and the relocation of local wildlife and plant life to new habitats.

The TBM will descend to 45m beneath the surface, passing below hard volcanic rock. "To create the launch pad for the machine, we first have to excavate through a significant chunk of this basalt to reach the softer soil conditions below," said Tommy Parker, state highways manager for Auckland and Northland, NZTA.

Excavation of the trench will involve a series of controlled explosions to fragment hard rock. "This not only allows the excavation to be carried out faster, it also significantly decreases the impact felt by local residents as it reduces the amount of traditional rock-breaking activity required," said Parker. "Basalt retrieved through this process will be used throughout the project, and forlandscaping."

Parker added: "In addition to local landscaping initiatives around Owairaka and Waterview, the project will, in partnership with Auckland Council, also provide enhanced walking and cycle ways between the two communities. These elements are vital components of the overall project scope, as we work to deliver this key transport link for Auckland."

The 5km Waterview Connection, including two 2.4km tunnels between Owairaka and Waterview, will provide a new six-lane motorway link between the Southwestern Motorway and SH20 the Northwestern Motorway to complete Auckland’s Western Ring Route. It is the country’s largest roading project to date.