Customer: Wellington Water
Location: Wellington, New Zealand
Wellington Water awarded McConnell Dowell the Barber Grove to Seaview Wastewater Treatment Plant Pipe Duplication Project.
This project located in Wellington, New Zealand’s North Island, involves the installation of a new 1.2 km long of one metre diameter pressurised wastewater pipeline from Barber Grove Pump Station to the Seaview Wastewater Treatment Plant. This new pipeline will service 90 percent of the residents in Hutt Valley, improve water quality to cater to the region’s growth and provide a robust solution in the event of earthquakes.
During the design phase, an area of geotechnically stable ground was identified as more resilient in a seismic event. Targeting this zone for the pipe installation resulted in the depth of the pipeline ranging from between 2.5 metres and nine metres below ground level. A high-water table across the site meant the temporary works along the alignment was extensive to ensure a safe and productive site. As one of the main arterial traffic routes in the region the local council was involved early on in the Early Contractor Involvement (ECI) phase to ensure works could progress while maintaining traffic flow at all times.
The ECI team reviewed a number of options and carried out multiple workshops with key stakeholders to develop a construction methodology that was the most efficient while causing the least possible disruption to the road network, residents and businesses and minimising our environmental impact.
Our solution involves a mixture of trenchless technology (55 per cent) and open trenches to install the pipeline. This method was chosen because it is the most efficient and will cause the least possible disruption to the road network, local residents and businesses.
The pipe will be laid by open trenching from Barber Grove pump station to Randwick Road. A Micro tunnel boring machine will be utilised from Randwick Road to the roundabout. This involves four excavation points along Randwick Road (approximately 200 metres apart) to set up the tunnel boring machine, with the final excavation at the roundabout. At the roundabout, the existing pipe sleeve underneath the Awamutu Stream would be used to bring the pipe to the Hutt City Carpark and the sleeve underneath the Waiwhetu Stream to bring the pipe onto Seaview Road. Accessing these sleeves will involve excavation on both stream banks. Open trenching would then connect to the Seaview Wastewater Treatment Plant.
Key to success
By working closely with key stakeholders early in the ECI phase, we have been able to ensure all parties are well informed and the construction methodology has been tailored to best accommodate the stakeholder needs.
During the ECI process, we were able to assist with detailed design and optioneering. This resulted in a final design that was fit for purpose while being aligned with the construction methodology.