Central Interceptor reroutes link sewer to avoid community disruption and reduce emissions

A design change that removes the need for one of the construction shafts on our Central Interceptor project is a win for the environment and the Blockhouse Bay community.
 
We have found a way to reroute the first of two link sewers connecting to the 14.7km wastewater tunnel, removing the need for a 30-metre-deep construction shaft at Whitney St.
 
Central Interceptor executive programme director Shayne Cunis says the route change is a major win for Blockhouse Bay residents and businesses.
 
“This is great news for this west Auckland community. We always try our hardest to minimise disruption during any infrastructure project and I’m really pleased our engineers came up with this innovative approach.
 
“The original plan included a 30-metre-deep shaft at Whitney St to allow our micro-Tunnel Boring Machine Domenica to be retrieved, serviced and relaunched part way through digging the first link sewer.
 
“Now, instead of two shorter drives, the micro-TBM will complete a longer, slightly curved drive which means we won’t need the Whitney St shaft and the traffic disruption it would have caused.
 
“At 1193 metres, this will be the longest micro - TBM drive of its type completed in New Zealand and sets a new standard for what this technology can deliver.”

Starting next year, Domenica will travel from the Dundale Avenue site directly to the Miranda site, followed by one last short drive to the existing wastewater pump station in Miranda Reserve to complete her journey for this link sewer.
 
Cunis says the design change also significantly reduces the project’s carbon footprint.
 
“By removing this construction shaft, there’s a huge carbon saving – our conservative estimates put the carbon savings at 200 tonnes of carbon dioxide equivalent (tC02-e). This takes into account materials like concrete and steel that won’t be used, and truck movements for spoil removal that are no longer needed.

“The whole Central Interceptor project is about cleaning up the environment. When it’s finished in 2026, it will store and transport both stormwater and wastewater to our Māngere Wastewater Treatment Plant, preventing wet-weather overflows and significantly cleaning up our waterways.

“And while the environmental outcomes of this project are huge, we’re also committed to finding ways to reduce our environmental impact during construction, which is why I’m so proud of the team for going back to the drawing board to explore alternatives to the Whitney St shaft.””
 
Cunis says the new approach means the tunnelling process will take a bit longer.
 
“It means the micro-TBM locomotive that travels back and forth transporting spoil will have further to go before it reaches the next shaft to be removed and trucked away. But in this case, the benefits far outweigh a change in operations.”
 
Whau Local Board chairperson Kay Thomas says: “Whau Local Board members are very pleased that disruption to the Whitney Street area has been avoided. We are grateful that Watercare is able to reroute the Central Interceptor pipeline work to ensure that Whau residents are not inconvenienced.”
 
Domenica laid the first underground pipe in June. Tunnelling is taking place 24 hours per day, five days per week, with the micro TBM travelling up to 15-metres per day. Domenica requires three crew members to operate, which uses a pipe-jacking method of construction whereby the entire tunnel is pushed along behind the mTBM.
 
Currently, Domenica is on track to complete break through on her first drive into the Haycock Avenue, Mt Roskill shaft in early December.
 
Meanwhile Hiwa-i-te-Rangi, the Central Interceptor’s main Tunnel Boring Machine that was launched in July, has laid more than 96 segments and travelled more than 160 metres of her 14.7km journey from Watercare’s Māngere Wastewater Treatment Plant to Grey Lynn.
 
A skeleton crew was allowed to work during Covid-19 alert level 4 lockdown to prevent the tunnel boring machines from getting stuck. Normal construction activity has since resumed in level 3.