Link Alliance TBM holes through in Auckland

21 October 2021

An important milestone has been reached on the Auckland City Rail Link (CRL) in New Zealand following the breakthrough of a Herrenknecht EPB TBM into Karangahape Station.

Operated by CRL’s main contractor Link Alliance, the 7.15m-diameter EPBM ‘Dame Whina Cooper’ cut through a 100mm-thick protective wall of concrete 32m below ground into the Karangahape Station cavern, having tunnelled 860m since its drive began at Mount Eden station in May 2021.

Operating 24/7 at peak, the 12-crew machine was built in Herrenknecht’s factory in Guangzhou, China and shipped to New Zealand in sections. During its drive it has encountered East Coast Bays Formation rock of the Waitemata group – primarily comprising sandstones and mudstones.

But the success of the Karangahape breakthrough has been tempered by covid’s continuing consequences for the project. “It is very clear, and it shouldn’t surprise anyone, that the pandemic has had serious impacts on our project costs and construction timings,” said Dr Sean Sweeney, City Rail Link’s CEO. “Assessments are underway now so that we have a much clearer picture of the extent and depth of covid’s effects on us.”

New Zealand’s recent five-week-long covid lockdown delayed the TBM’s planned breakthrough in September. However, Link Alliance continued to operate the machine during the lockdown, well below full capacity, to stop earth settling around it. Tunnelling accelerated when lockdown restrictions eased.

The machine will now complete the final leg of this first 1.6km drive when it arrives at Aotea Station in central Auckland in early 2022, thereby linking with the CRL tunnels already built from the Britomart transport hub. It will be dismantled at Aotea, returned in sections to Mount Eden, and reassembled to start boring the second tube in 2022.

The largest transport infrastructure project ever undertaken in New Zealand and the country’s first underground railway, the US$3.2bn CRL will connect Britomart and Mount Eden Station on the Western Line with 3.45km of tunnels under central Auckland. With a capacity of up to 54,000 people an hour, CRL is expected to transform Auckland’s public transportation network. Completion is scheduled for late 2024.