Lockdown risk removed for CRL’s TBM - The 130 m City Rail Link’s TBM, named after Dame Whina Cooper, costing around $13 million and built specifically for Auckland’s soil conditions, is continuing to work: it has covered 328 m, installed 205 rings towards Mercury Lane and removed 26,000 t of earth.   

City Rail Link Ltd has advised the Government that it will operate its TBM at the reduced level allowed under current Covid-19 health and safety regulations. TBMs are not designed to be parked underground for an open-ended period – they need  to keep moving forward, even at reduced capacity, to avoid the risk of getting stuck. The low-level operation will remove the risk of pressure from earth settling around a stationary TBM and trapping the machine. If that happened here, the costs and time involved in freeing the TBM would be catastrophic and completely derail the project.  

The TBM is operated by CRL’s main contractor, the Link Alliance. The machine began excavating the first of the project’s two rail tunnels in May – driving from Mt Eden first to Karangahape and then on to central Auckland to connect with already constructed tunnels from Auckland’s downtown. When the TBM arrives at Karangahape Station it will push itself through the mined tunnel on temporary rails. 

The TBM will first pass through MC30 - the southbound mined tunnel - that has been excavated using a combination of road headers and excavators. This methodology was selected to enable both parts of the project – the station entrance box and tunnels - to be constructed concurrently, creating efficiencies for the project program. Please click here to follow the TBMs progress.  

Breakthrough at New Zealand’s deepest railway station 

On the 05/08/21 a key milestone was reached in Mercury Lane with the underground breakthrough from the City Rail Link’s Karangahape Station box to the mined pilot tunnel below (click here for the video):  the two sections of New Zealand’s deepest railway station are now joined together as a result. The breakthrough occurred 18 m below the station entrance under construction at Mercury Lane. 

A combination of vibro ripper and hammer working inside the station entrance excavation has chiseled its way through layers of rock to open the hole in the roof of the pilot tunnel below. This has been constructed underneath the footprint of the station box in advance of the station construction, in order to provide access to multiple work fronts for the mining team and used to excavate the platform tunnels. Before the breakthrough, the pilot tunnel was backfilled with spoil from the mined tunnel, eliminating the risk of machinery falling into the tunnel from above, or debris falling if the breakthrough had been tackled from below. 

Construction of the station building below street level began in early March and within five months, it has laid the concrete slabs for two of the station’s floors, removed 16,000 cubic metres of spoil, and joined up with the mined tunnels beneath. 

The first three levels of the station, entrance -  L0, B1 and B2, are now completed.  The Mercury Lane team is excavating to the deepest floor B7 and the methodology will change to 'bottom up' construction, that consists of excavating / rock bolting / shotcreting. 

With access now available from both the underground station and the mined tunnels, there is more flexibility to share resources between teams to excavate the remaining 16,500 cubic metres of rock for the station. 

With the mined tunnels, excavation work is now complete on the southbound platform tunnel closest to Mercury Lane and work has now begun on the northbound tunnel closer to East Street. The platforms will be 203 m long to accommodate nine-car trains instead of the current six used on the Auckland network.  

With the completion of the tunnels the floor is lined with a layer of concrete called blinding, making it ready for the installation of temporary rails for the arrival of CRL’s TBM’s from Mt Eden in September.  

One of the city rail link Karangahape station platform tunnels under construction by Link Alliance

When completed Karangahape will be 32 m below ground. A completed CRL and its two underground stations will give New Zealand’s largest city a world class railway - improved access in and out of central Auckland and quicker and more frequent trains across the wider city.  

Click here and nz/15 for more details of the project in the tunnelbuilder archive and also visit https://www.cityraillink.co.nz/. 35/21.