Amīria, McConnell Dowell’s micro tunnel boring machine (mTBM) beat her previous project record by 80-metres on 20 November 2020.

The AVN2500 mTBM once again set a new pipe-jacking record for the longest single drive in the Southern Hemisphere by a TBM greater than 2.6 metres in diameter. The project set a 1,216-metre record on completing the second drive for the pipeline earlier in the year.

Richard Atkin, the Hunua4, Section 11 Project Manager, said “I couldn’t have asked for a more experienced tunnelling team to successfully navigate through Auckland’s challenging volcanic fields which comprise of hard basalt (up to 160MPa). To gain another record for this project after 18 months of tunnelling, across three individual drives, has put the team in good spirits as we near the finish line.”

The new record is a hard-earned achievement for the team delivering the 3.5-kilometre watermain upgrade for Watercare. The final 1,296-metre drive consisted mostly of basalt rock and tough clay ground conditions, but despite the geological challenges, the crew completed the final drive in less than three months.

Justin Shepherd, McConnell Dowell’s Tunnelling & Underground Group Technical Director, praises the efforts made on Hunua 4, Section 11 by saying “McConnell Dowell challenges both the norm and ourselves by thinking creatively, engaging our multi-discipline specialists, embracing new technology, and driving continuous improvement through our teams and projects. This project, which we believe to be the longest large diameter pipe-jacked drive through ‘continuous hard-rock conditions’ in the world, exemplifies McConnell Dowell’s approach to successfully delivering award-winning, and record-breaking, tunnelling and underground work.”

With 2.9 kilometres of tunnelling now completed, Amīria, one of McConnell Dowell New Zealand’s three mTBMs will be refurbished by our in-house mechanical and maintenance team.  The next step for the project team is the installation of the 1,575 mm diameter concrete-lined steel (CLS) watermain pipes inside the tunnel which is planned for early 2021.

McConnell Dowell’s proposed trenchless methodology won the contract to design and construct the final section of the Hunua 4 pipeline in 2018. Rather than digging trenches through some of Auckland’s busiest roads, the  tunnelling approach meant traffic continued to flow between Epsom and the city as the pipeline was built underneath.