Taking the strain - historic CPO building shifts again for CRL
Auckland’s historic Chief Post Office (CPO) is on the move again – work has started on the intricate job of transferring the 14,000-tonne heritage-listed building from temporary support on to new permanent foundations above the City Rail Link tunnels built through its basement.
“It’s a very short journey – 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’s Head of Delivery, Scott Elwarth.
Scott said those three millimetres are the most the 107-year-old building is allowed to move as its weight settles on new foundations.
“Underpinning a building the size and weight of the CPO is an extremely challenging task – something only done when other methods are not available and, then, done very slowly.”
Buildings like the old Birdcage Tavern near Auckland’s Victoria Park road tunnel have been physically moved out of the way before, but Scott said there was no room in central Auckland to do that for a building as large and as heavy as the CPO.
“The CPO is one of the most historically important buildings in the country – a building with a top heritage rating. All our planning, design and construction of the tunnels has been dominated by the need to protect the CPO from any damage. Add in the tight working conditions for our teams under all that masonry and concrete and the ‘live’ Britomart station on the other side of the wall, then you’re dealing with a challenging engineering operation,” Scott said.
The weight transfer will be gradual, over several weeks. It includes removing some 350 tonnes of steel used for the underpinning structures that provided temporary support for the building during tunnel construction.
“It’s a delicate, careful and well-planned operation,” Scott said. “People will not notice any change to the CPO”.
The CPO’s latest “journey” reverses one completed last year when its weight was transferred to temporary supports and 15 original concrete foundation columns demolished to clear the way for the tunnels.
The return “journey” will be completed at the end of October when the building will be supported securely on new foundations that include “diaphragm walls” sunk 20 metres below ground, new foundation columns, cross beams and the tunnel boxes themselves.
After the weight transfer, work will start on restoring the CPO’s interior. Restoration work will be completed in late 2020.