Our Central Interceptor tunnel completes undersea crossing of Manukau Harbour

Hiwa-i-te-Rangi has completed manukau harbour crossing

With a few turns of the cutterhead, Hiwa-i-te-Rangi, our Central Interceptor Tunnel Boring Machine (TBM) will today (6 December) make landfall—and history, as she arrives in Hillsborough after successfully crossing Manukau Harbour en route to central Auckland.
Hiwa-i-te-Rangi left Māngere Bridge in September, completing the 1500m undersea stretch smoothly in just 11 weeks. The 5.4m diameter cutterhead will bore into a 25m deep shaft next to our wastewater pump station overlooking the harbour at Frederick St. It will be an exciting moment for the project team, who is building a $1.2b supersize underground tunnel from Māngere Wastewater Treatment Plant to central Auckland to reduce wet-weather overflows and clean up waterways.
Our executive programme director, Shayne Cunis says it’s rare in New Zealand for undersea tunnelling to occur and achieving this milestone is a huge credit to the team: “We’ve got some very talented tunnellers and their knowledge and expertise has showed all the way along this project—but especially with the completion of the Manukau Harbour section. It’s a big relief to get this done successfully and the fact that it comes just before Christmas, means everyone can enjoy a well-earned holiday break.” 
Ghella Abergeldie JV is delivering the Central Interceptor project. Tunnelling took place at 15-20m below the seabed, with a maximum of 15 crew working 24/7 underground at a time.
This is the third undersea tunnel that Ghella Abergeldie JV’s Tunnel Manager, Michele Petris has worked on—his last project was to build the new Metro tunnel under Sydney Harbour: “I am very proud of our team. From a technical perspective, tunnelling under the seabed is no different to tunnelling on the mainland but the difference is that in the event of an emergency, then rescues become more difficult.
We wanted to ensure there were no hold-ups or delays while we did the undersea section and we achieved that. Now we will inspect the cutterhead and see if any adjustments need to be made before we begin tunnelling again towards central Auckland.”
Hiwa-i-te-Rangi began her journey in August last year and has now travelled more than four kilometres since leaving a site next to Māngere Wastewater Treatment Plant on Greenwood Rd. The 4.5m diameter tunnel is made up of concrete rings, formed by six concrete segments that are fixed together underground. 10-12 completed tunnel rings are laid each day. Spoil travels through the cutterhead, along the length of the nearly 200m TBM via a series of conveyor belts, before tipping into “muck skips” which travel to the tunnel entrance via electric locomotives. A gantry crane lifts the muck skips out of the shaft and the spoil is deposited at nearby Puketutu Island, where we are carrying out a rehabilitation project at a former quarry.
Hiwa-i-te-Rangi’s cutterhead will be inspected before tunnelling begins again in a few days, as she heads towards Keith Hay Park, Mount Roskill almost two kilometres away.  
Meanwhile work on building the first link sewer (running from May Rd, Mt Roskill to Avondale) is progressing well, with a micro-TBM called Domenica having just achieved her third breakthrough, after arriving at Miranda Reserve in November. She will travel another 300m to complete the link sewer before she’s refurbished ahead of work on the second link sewer next year.
Earlier this year, Auckland Council and us announced that the Central Interceptor tunnel would be extended from Tawariki St, Grey Lynn to Pt Erin to capture combined wastewater and stormwater flows in Herne Bay. Consent applications for the tunnel extension will take place early next year.