Last week the TBM EPB Hiwa-i-te-Rangi, involved in the construction of the 14.7-km-long and 4.5m diameter wastewater tunnel from Grey Lynn to Māngere Wastewater Treatment Plant at Auckland, started tunnelling the 1500 m across the Manukau Harbour. It will take around four months to complete at depths of 15-20m below the seabed.
The NZD 1.2bn Central Interceptor project will cut by over 80 per cent wastewater overflows into the Waitemata Harbour from the western isthmus and it will help ensure clean beaches and harbours. Stormwater infiltrating into wastewater has caused overflows into Auckland’d harbours and waterways for a century.
The TBM Hiwia-i-te-Rangi - working 24 h/7days - has travelled over 2681 m and installed 1669 rings formed by six concrete segments since it was launched in August last year from Māngere Treatment Plant. The contractor is the Joint Venture Ghella Abergeldie.
Recently, Hiwa-i-te-Rangi was checked thoroughly, including the cutterhead. More than 30 cutting discs have been swapped for rippers for maximum efficiency as it powers its way through East Coast Bays Formation rock all the way to Grey Lynn.
Each day, Hiwa-i-te-Rangi travels up to 16m and lays eight to 10 tunnel rings. The tunnel has a coloured plastic liner to protect against the corrosive effects of wastewater to give it a design life of 100 years. The colour changes indicate different steel reinforcement in the segments which are governed by the changing geology. The TBM was launched in the most challenging soil conditions: Kawa sands and the liner was blue. As tunnelling has progressed, grey and pink tones have emerged. Half-way across the Manukau Harbour, the liner will change to yellow, as the ground changes to East Coast Bays Formation sandstone rock.
The harbour crossing will be closely followed by another of the Central Interceptor’s tunnelling team, who are building the first of two branch sewers. The team is operating a micro-TBM called Domenica. So far, it has made two breakthroughs as it travels from May Rd, Mount Roskill en route to Miranda Reserve, Avondale.
For further information click here and nz/18 for tunnelbuilder archive. Visit https://www.watercare.co.nz/. 39/22
