Construction update for the tunnels beneath the CPO building
A lot has happened in a year. The above photos show the progress from this time last year to now. We’ve also hit some pretty cool milestones which are listed below.
Escalators
Sixteen sections of the new metro-grade escalators have been lifted in to the City Rail Link (CRL) tunnels below the Chief Post Office (CPO) building - ready for installation in Britomart Station.
C1 design manager Andrew Swan said lifting the escalator sections into the restricted space of the CRL tunnels was a challenging task. “The delicate operation of lowering the escalators between the Lower Queen Street structural struts and the remaining section of open tunnel roof took two days to complete.”
Each escalator is delivered in four sections with the heaviest section weighting 4900kg. These will be manoeuvred through the tunnels on skates into the station where they will be bolted together before being moved into their final positions.
The installation process will begin soon and once complete, the escalators will move passengers 30 percent faster than the existing commercial-grade escalators. They are the heaviest duty escalator available – specifically designed for this type of application and it will be the first time they have been used in New Zealand. For more information on the metro-grade escalators please click here.
Underpinning
The historic Chief Post Office (CPO) is now resting on its permanent foundations, which have designed to last for at least 100 years. For the past two years the 14,000 tonne, Category 1 heritage CPO building had its load temporarily transferred onto a series of concrete and steel underpinning structures.
Constructing the CRL tunnels has also involved constructing new permanent foundations for the building and the building loads have now been transferred back onto these permanent structures.
To do this, contractor Downer Soletache Bachy Joint Venture had to hold the building in position and swap out the foundations.
“Movement is tightly limited – three millimetres at most – but it’s one of the most demanding engineering jobs undertaken in New Zealand and one rarely done overseas,” said CRL Head of Delivery, Scott Elwarth.
The load transfer operation was completed in early October - a significant project milestone not only because it completes a phase of highly technical engineering, but it also allows reinstatement of the ground floor of the building to commence.
Breakthrough
The reinforced concrete walls once separating Britomart Station’s train platforms and the CRL tunnels under the CPO building are now no longer; they have been demolished.
It’s a small step but a symbolic one as it opens Britomart up to rest of the CRL project and will eventually allow the station to become a through station, rather than a terminus station (dead-end stop).
Until the break-through, construction workers had been accessing the tunnels beneath the CPO building – that extend underground all the way up to Albert Street – through the works site in Lower Queen Street.
Tunnel box completion
The final sections of tunnel roof in Lower Queen Street will be complete by the end of November. Once complete the only way to access the tunnels will be through Britomart Station and backfilling of the excavation in Lower Queen Street will commence in earnest.