As the first of two connecting sewers to the main tunnel, Link Sewer C is completing by a micro-TBM on Auckland’s Central Interceptor project.
Been commissioned in June 2021, the 2.6m diameter Domenica has completed four shaft breakthroughs along the 3.2km link sewer tunnel route in New Zealand’s largest city. In order to significantly decreasing wet-weather overflows, the tunnel is due to take stormwater and wastewater to Mangere treatment plant for processing.
The “big moment”, is the description of Central Interceptor commercial manager Nigel Varcoe about the breakthrough, which was four weeks ahead of schedule.
“We’ve been through a lot: a global pandemic, closed borders and more recently floods. To have the first link sewer tunnel completed safely and ahead of schedule is a great achievement and I’d like to pay a particular tribute to the Ghella Abergeldie JV tunnellers who have worked so efficiently to get the job done,” Varcoe said.
Operation of Domenica is undergoing using a pipe-jacking method of construction and a crew of 15 people, working above and below ground.
Domenica laid around four to five pipes per day on average and travelled up to 15m, five days per week.
According to Surface and permanent works delivery manager Chris McCarthny: “There had been challenges. In November, Domenica completed the longest drive of the project (1212m) from Dundale Ave, Blockhouse Bay to Miranda Reserve. Not only was it a very long continuous drive, but the tunnel was also curved, which was technically challenging.”
He also added: “The long drive was necessary because a design change removed the need for another shaft at Whitney St, which would have caused months of disruption for Blockhouse Bay residents, so we’re very grateful to the team for pulling this off.”
Before commencing work on link sewer B in late July, Domenica will be removed for refurbishment. With over 1km long, this link is slated to just involve two separate drives.
The TBM, Hiwa-i-te-Rangi, which was launched in August 2021 and is the Central Interceptor’s main TBM, has just completed a 5km landmark on the 14.7km bore towards central Auckland and is currently 115m underneath Hillsborough Ridge – the deepest section of the journey. Daily performance of Hiwa-i-te-Rangi is up to 25m and is powered by a series of thrust cylinders. So far it has laid 3,118 steel-reinforced concrete rings to create the main tunnel, which has a 100-year lifespan.
As the largest wastewater project in New Zealand’s history, the Central Interceptor will store 226,000m3 of wastewater, control the flows into treatment plants and reduce the number of wastewater overflows.