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Customer: Watercare, New Zealand Contract: Construct Location: Clarks Beach, Auckland   |
Fast Facts:
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Our latest tunnelling project win, the new South-West Outfall, is McConnell Dowell New Zealand’s 15th outfall project and will be our eighth TBM ‘marine recovery’. This is also our first project for Watercare after being selected for their Asset, Upgrades and Renewals (AUR) Panel.
Clarks Wastewater Treatment Plant (CWWTP) currently serves 2,500 people in Clarks Beach and Glenbrook Beach and is currently being upgraded to service up to 6,000 people, which is expected to cover growth up to 2030.
The Clarks Beach Wastewater Treatment Plant is located in the middle of the Clarks Beach Golf Course, which presented some challenges. Using trenchless technology to install the outfall means golfers can drive along the 12th hole fairway while we drive the pipeline about 12m below them underground.
Most of the works will be carried out within the existing plant footprint but a robust traffic management plan (TMP) was needed for large construction vehicles such as the 110T crane and 19.5 tonne TBM.
We have been on site since October last year, removing the median island along a section of Stellar Drive to create safe access for trucks and other plant and filling in part of an irrigation pond to build a two-lane access road.
A total of 240m of steel casing pipes will be driven from the launch trench toward the coast using the Direct Pipe® jacking system. Half, or 120m of the outfall, will be under land, and the other half will extend out under the Manukau Harbour, where it will breach the seafloor.
Once the PE liner pipes are installed, seven permanent steel piles will be driven into the harbour floor from a jack-up barge. The remaining 66 m of PE pipeline will be installed, along with 22 diffusers to help disperse treated wastewater and prevent fish from entering the outfall.
We plan to use a sling, connected to a custom-designed double-pontoon floatation device, to ‘recover’ the TBM from the harbour. Once the TBM is winched up beneath the pontoon, it will be towed about 30km to Onehunga Wharf, where it will be lifted out of the water.
The outfall is sized to service long-term growth in the wider southwest community. It will be fit for purpose, able to carry the treated wastewater created by up to 30,000 people.
The map of the Southwest Outfall shows its Clarks Beach location
It includes the route the custom pontoon will follow to tow the recovered mTBM approximately 30 km from Clarks Beach to the Onehunga Wharf, where it will be lifted from the water.
The inset shows the worksite below the existing wastewater treatment plant and the surrounding Clarks Beach Golf Course, as well as the tunnelling and outfall alignment.
