Daldy Street Outfall

David Pattinson (Wynyard Edge Alliance – McConnell Dowell, Downer, Beca, Tonkin & Taylor, Auckland Council & MBIE)

To install the largest pipe laid in New Zealand, five metres deep, through
contaminated ground, and under tidal conditions was a challenge in itself. To do
this whilst precluding entry into the trench during installation seemed like too
great an opportunity to miss. Plain sailing for the Wynyard Edge team!
As a variation to the Americas Cup infrastructure project, this critical element of
work involved installation of 510 metres of 3.5 metre diameter HDPE pipe, under
tidal conditions. Key to the success of the project was the innovative temporary
works specifically designed for the challenging conditions - installation of a cutter
soil mixed retaining wall to support the excavation, the installation of concrete
cradles to support the ends of each pipe in the excavated trench, supporting the
cradles on inflated grout bags under water, and sinking the lightweight pipes below
the rising / falling tide.
More importantly, the whole process was designed to preclude entry into the
trench during installation, a huge safety benefit. The pipeline also included a new
featured outfall with a darkened, patterned face blending it in with the surrounding
basalt breakwater. The project was completed on time, under budget and incident
free with a delighted Client - the innovative temporary works being critical to its
success.