Ask Phoebe: Life yet for Alice after Waterview tunnel job

The tunnel boring machine with its distinctive silver fern at Herrenknecht's factory at Guangzhou, China.

When the tunnel boring machine Alice has finished tunnelling the SH20 extensions in Waterview, what will happen to her? Will she be thrown away, buried in the ground, sent back to China, stored for future use, or used to dig some more tunnels in New Zealand?

Vinnie Beckett, Auckland.

Because of the work she is designed for, Alice will not necessarily be suitable for other tunnel projects in New Zealand. The machine's ultimate fate will be decided at the end of the project when the NZ Transport Agency returns Alice to the German company responsible for her construction, Herrenknecht. The company will decide whether Alice will be refurbished or sent directly to another tunnelling job, which could be anywhere in the world.

Where is all the dirt and rock from the Waterview tunnel going to be put? There will be a big heap. Clive Tomkins, Auckland.

The project requires about 1.3 million cu m of spoil to be removed to a former quarry site in Wiri, 800,000 cu m of it from the tunnels. As well, about 100,000 cu m of hard basalt rock has been removed from the Alan Wood Reserve in Owairaka. The basalt is from a lava flow and is up to 14m thick in places. It was removed so that a trench could be excavated in time for Alice's arrival.

The trench will ultimately be used as part of the motorway to and from the southern portals of the Waterview tunnels.

The basalt is taken to the Wiri quarry where the project has established a crushing plant. Some of the crushed rock will be trucked back to Waterview to be reused on the project and the surplus is being sold as metal for gabions, road foundations and backfill.

Gabions are those wire cages filled with rock that are used for erosion control and trendy garden walls, among other things.

The project has also established a landfill at the quarry for disposal of the tunnel material. This means that over the life of the Waterview project, the old quarry will be rehabilitated ready for redevelopment as a commercial area.

As I travel along the Northwestern motorway by the Whau creek, work is progressing on widening the seaward side of the motorway. There used to be two islands here, Pollen and Traherne islands. Traherne Island appears to have disappeared due to this widening. How about Pollen Island? Does any remnant of it remain? It used to be a sanctuary for sea birds in the past.

Tony Goodwin, Avondale.

Traherne Island has not quite disappeared. It may lose up to 3m where it borders the motorway, but a lot of work is being done to compensate, including weed control, pest control, lizard surveying, moth surveying, and salinity monitoring.

Pollen Island remains. During the causeway upgrade, special measures will be taken to reduce the impact on the marine reserve.

Data gathered from trials in the past couple of years will be used during construction to monitor the effects on birdlife and the environment.