Due to the difficult ground conditions and high traffic volumes, Wellington Water said trenchless tunnelling was the preferred method for installation.
The Barber Grove to Seaview Wastewater Treatment Plant Pipe Duplication is located in the Lower Hutt region of New Zealand.
Local utility Wellington Water is working on behalf of Hutt City Council and Upper Hutt City Council jointly, duplicating the existing water main by installing a new 1200 m long, 1000 mm diameter rising main from Barber Grove Pump Station to the Seaview plant.
The existing pipeline currently conveys wastewater from 90 per cent of Hutt Valley’s residents. It is also more than 50 years old and is highly vulnerable to earthquakes.
The new pipeline is designed to reduce the risk of wastewater entering Te Awa Kairangi and the Waiwhetu stream in an earthquake.
“With pipes like these nearing the end of their useful lives, coupled with the growth we’ve been experiencing, our infrastructure is under pressure and it’s crucial we invest before a significant event,” said Hutt City Council Mayor and Chair of the Water Committee Campbell Barry.
“This project builds resilience into our network, and ultimately protects our environment now and into the future from wastewater overflows.”
Wellington Water will work alongside design partner Stantec, and has awarded the tunnelling contract to McConnell Dowell.
Together they have devised a solution involving a mixture of trenchless technology (55 per cent) and open trenches to install the pipe.
According to Wellington Water, due to the difficult ground conditions and high traffic volumes, trenchless tunnelling methods were the preferred option.
According to McConnell Dowell, this method will prove the most efficient and will cause the least disruption to the road network, local residents and businesses.
McConnell Dowell managing director for New Zealand and the Pacific Fraser Wyllie said this project would continue to build the company’s track record of constructing pipelines using trenchless methodologies in the country.
“We are excited to work with our new client Wellington Water in the delivery of the new pipeline which will service 90 percent of the residents in Upper Hutt and Lower Hutt, improve water quality to cater to the region’s growth and provide a robust solution in the event of earthquakes,” Fraser said.
The project will consist of 1.2 km by 1 m diameter in polythethylene pressurised water pipeline installed 3 – 9 m below traffic routes.
Four shafts will also be constructed along Randwick Road for access to the tunnel, and 55 per cent of the alignment will be installed via microtunnelling.
Works are expected to commence in February 2023 with completion due early 2023.