Tunnelling under NZ’s Harbor has started for the city’s Central Interceptor wastewater system.
The Hiwa-i-te-Rangi TBM is going to bore a 1500m tunnel across the Manukau Harbor, which is the toughest part of her 14.7km journey from Mangere to Grey Lynn. Tunneling is said to be at depths of 15-20m and should be finished in approx. four months.
Before starting this phase, over 30 cutting discs were exchanged for rippers of max efficiency as the Herrenknecht EPBM is going to tunnel through East Coast Bays Formation rock to Grey Lynn. The TBM which is 5.4m in diameter is going to progress 16 meters per day. It has already excavated 2.5km from the Mangere Treatment Plant on the south side of Manukau Harbor.
It is worth mentioning that Ghella Abergeldie JV is the chief contractor on the NZ$1.2bn project.
This tunneling under a key New Zealand harbor has taken place for the first time, yet Watercare has bored under smaller sections of water before, containing the Orakei Basin, to build the Hobson wastewater tunnel and a 600m stretch for the Rosedale Wastewater Treatment Plant outfall pipe.
Program Director Shane Cunis stated that there is a potential risk of flooding if water seeps through the cutter head, so detailed work on the TBM beforehand has been essential. But if something goes wrong, the machine is equipped with two safety chambers that can hold 40 people for up to 24 hours.
The harbor crossing is going to be followed carefully by the Central Interceptor’s other tunneling team, which is operating Domenica, a micro-TBM to construct the first of two branch sewers.
The largest wastewater in New Zealand’s history i.e., the Central Interceptor, is going to hold 226,000m3 of wastewater, control the flows into treatment plants and decrease the number of wastewater overflows.
The TBM is anticipated to reach dry ground in Hillsborough by December.