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Customer: Wellington Water Location: Wellington, New Zealand Contact: Construct   |
Fast Facts
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McConnell Dowell was awarded a contract by Wellington Water to deliver the Trunk Main Duplication Project from Barber Grove to Seaview.
This project located in New Zealand’s North Island, involves the installation of a new 1.2km, 1m diameter pressurised wastewater pipeline from Barber Grove Pump Station to the Seaview Wastewater Treatment Plant. This new pipeline will service up to 120,000 people in Upper Hutt and Lower Hutt, improve water quality and provide a robust solution to cater to the region’s growth.
McConnell Dowell were selected in February 2021 as ECI partner to help finalise the design and several construction options were discussed with respect to their impacts on the community and the environment. The construction method chosen is a 55% trenchless method to provide the least disruption to the residents while maintaining multiple work fronts to meet the project schedule.
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 (approx. 200m 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.
The challenge
During the design stage, 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 three 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 ECI phase to ensure works could progress while maintaining traffic flow at all times.
The solution
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. The selected method for construction was 55% of the mainline which will be installed via microtunnelling with the remainder being installed via open cut.
The Barber Grove project was the successful winner of 'Category C' (projects in excess of $3million) at the CCNZ Wellington/Wairarapa Branch 2024 Excellence Awards
