Outfall pipeline creates opportunity to set new tunnelling world record The Snells Algies wastewater pipe and outfall construction project was the first phase of a three-stage scheme to supply the Warkworth and Mahurangi East communities north of Auckland, New Zealand, with reliable wastewater services to cater for population growth. The scheme will improve water quality in the Mahurangi Harbour and deliver an upgraded wastewater system. McConnell Dowell was awarded the design and construct contract by Watercare in March 2019. It continues to build on McConnell Dowell’s extensive track record in the construction of major marine outfall pipelines in New Zealand. Our solution featured the use of the Direct Pipe® system to install a trenchless pipeline to minimise disruption to the farmland and local environment. The project involved the following elements of construction: • Constructing 4.3 kilometres of 630mm diameter HDPE pressure/gravity main by open trench methods following the public road alignment. • Installing 2.02 kilometres of 1.2 diameter steel pipe using the Herrenknecht Direct Pipe® system under private farmland out to a marine recovery trench 550 metres off the coast. • Laying a 230m marine outfall pipeline with 80m diffuser section on the seabed for disposal of highquality treated effluent into the Hauraki Channel. • An extension to the contract to install 530m of 710mm diameter HDPE pipe from the WWTP to connect to an existing pipe using horizontal directional drilling (HDD) across the Te Whau Creek. Snells Algies WWTP & Ocean Outfall Auckland, New Zealand
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