The end of four years of City Rail Link-related closure, construction and restoration was celebrated on 6 April, with Auckland’s historic Chief Post Office (CPO) being ‘returned to the city’, ready to resume its role as the front door for the Britomart Transport Centre.

The reopening followed a complex engineering feat to remove original support columns out of the way of the City Rail Link (CRL) tunnels and transfer the CPO’s weight to new foundations without damaging the historic building.

CRL Delivery Manager Scott Elwarth says that transferring the weight of the 109-year-old, Category A heritage-listed building onto temporary foundations to keep it protected during construction was one of the most complex engineering challenges seen in New Zealand.

“We had to work in some pretty confined spaces, under 14,000 tonnes of masonry building, to excavate reclaimed land below sea level with the Waitematā Harbour just across the road,” says Elwarth.

Temporary closure of the CPO in 2017 followed months of detailed planning, design and modelling, involving CRL, its contractors, Downer NZ and Soletanche Bachy (DSBJV), Auckland Transport, Auckland Council and Heritage New Zealand.

Work began in mid-2017 with the removal of the first layers of reclaimed land for a 14-metre-deep trench in lower Queen Street in front of the CPO.

Firstly, 340-tonnes of steel beams were required to span between rows of new piles (diaphragm or D walls) built either side of the CRL tunnels. The CPO’s weight was then transferred onto the beams to enable the construction of permanent reinforced concrete foundations below. The weight of the building was then transferred onto the permanent foundations.

Ongoing works within the station will see the temporary entrance building and temporary stairs removed, followed by additional work around track and platform configuration to prepare the station for CRL’s operation. Streetscaping around the CPO was set to be completed in May.