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Customer: Wellington Water Contract: Construct Location: Wellington, New Zealand   |
Fast Facts
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We used the optimum mix of tunnelling and trenched construction techniques to deliver the Barber Grove to Seaview Wastewater Treatment Plant Pipe Duplication Project for Wellington Water, causing the least impact possible.
The project involved the installation of a new 1.2 km long, 1 m diameter pressurised wastewater pipeline. It services 90% of the residents in Hutt Valley, improving water quality and catering to the region’s growth.
During the Early Contractor Involvement (ECI) process we reviewed several options and carried out multiple workshops with key stakeholders to develop a construction methodology that was the most efficient and had the lowest impact on the community and the environment. The final construction mix was trenchless (55%) and open trench (45%).
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 pipeline's depth ranging between 2.5 m and 9 m below ground level. A high-water table across the site meant the temporary works along the alignment were extensive to ensure a safe and productive site.
As one of the region's main arterial traffic routes, we involved the local council early on in the ECI phase, to ensure our works could progress while maintaining traffic flow at all times.
We trenched the pipe from Barber Grove pump station to Randwick Road. We then used a micro tunnel boring machine from Randwick Road to a roundabout. This involved four excavation points along Randwick Road (approximately 200 m apart) to set up the tunnel boring machine, with the final excavation at the roundabout.
At the roundabout, we used an existing pipe sleeve underneath the Awamutu Stream 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 involved excavation on both stream banks. We then used open trenching to the Seaview Wastewater Treatment Plant.
By working closely with key stakeholders early in the ECI phase, we ensured all parties were well-informed and were able to adapt aspects of the construction methodology to meet stakeholder needs.
This resulted in a fit-for-purpose solution delivered to our customer's satisfaction and with minimal impact on the community and the environment.
The Barber Grove project was the successful winner of 'Category C' (projects in excess of $3 million) at the CCNZ Wellington/Wairarapa Branch 2024 Excellence Awards
