Army Bay. Whangaparaoa
The Army Bay Wastewater Treatment Plant services Whangaparaoa Peninsula, Orewa, Hatfields beach and Silverdale. Operational since 1982, it treats wastewater and discharges it through a 2.8 km outfall pipe that extends 1.0 km out into the Tiri channel. The existing outfall pipe was not only aging, it was not of a size capable of dealing with the demands of future population growth. A new HDPE pipe was installed underground from the Plant to the shore line. From here it was connected to the new outfall pipe, the sections of which were weighted with concrete supports and sunk onto the sea bed.
Photo courtesy of www.skyhighnz.co.nz
Each pair of the hundreds of concrete pipe supports were held together by steel rods. The rod holes had to be patched with a solution that was both waterproof and corrosion proof. Multiple 450m lengths of the outfall pipe were assembled at Whakatiwau 100kms away and transported by barge to Army Bay so it was also crucial the patching solution would not crack when transported.
Factors to consider included the aggressive marine environment, the project time-frame, the considerable durability demands and the need to ensure the steel rods had permanent protection from corrosion.
Mc Milen Jacobs Associates
Mc Connell Dowell