One of the most complex engineering challenges for the City Rail Link (CRL) to date has just been completed and it has taken two years of planning and preparation by NZ and international experts.
In order to construct new railway tunnels under the Britomart train station, the building had to first be moved onto temporary foundations to keep it protected during construction.
The station is housed in the stately former Chief Post Office building in downtown Auckland. This building opened in 1912 and is classified as Category One heritage building.
Says Scott Elwarth, CRL’s Head Delivery Manager: “We had to lift the building by only two millimetres onto new foundations but so much depended on this being 100 per cent successful, there was absolutely no room for error. This is an historic and magnificent building and CRL is fully committed to preserving the built heritage of the building.”
“In all, we had to transfer 4000 tonnes of the building weight onto a series of underpinning frames to protect it from moving while tunnel construction happens.”
The feat drew comparisons with another Auckland infrastructure project. In 2011, engineers successfully moved the 740-tonne 1886 Birdcage hotel building back to its original site near Victoria Park. The hotel had been moved about 40 metres to allow for work to begin on building the Victoria Park tunnel.
Britomart train station currently has has “dead-end” tunnels meaning Auckland’s trains end their journeys there. The CRL will change that by extending those tunnels and creating a two-way through station with a 3.45km underground rail link up to 42 metres below the city centre.
There will be new stops – an underground station mid-town with entrances at Wellesley and Victoria Streets and one off Karangahape Road with entrances at Mercury Lane and Beresford Square.
The present Mount Eden station near Eden Terrace will be re-developed and the CRL tunnels will connect there with the North Auckland (western) line.
The result will be a better connected the Auckland rail network.
Nick Adams, in charge of the construction for the CRL’s C1 contract, which includes Britomart, says constructing temporary foundations beneath the building was a difficult enough operation given the available space, head height and depth of underlying bed rock, let alone transferring the weight of the building onto these foundations.
Before construction of the new rail tunnels could begin, significant “enabling” activities needed to be undertaken.
This included construction of temporary accommodation for the train station’s operations, construction of a coffer dam to house the rail tunnels and installation of the underpinning structures.
“All aspects of the construction need to be undertaken carefully given the key requirement not to disrupt station operations nor adversely affect businesses and other neighbours.”
A multi-national team of experts added their expertise to ensure the operation was successful.
Nick says the project and especially this complex achievement has been a career highlight. “I’ve worked on a number of large infrastructure projects both in NZ and overseas and this one is a great challenge. I’m very proud and satisfied to be playing my small part in making my home town of Auckland a better place to live and work.”
CRL’s CEO, Dr Sean Sweeney, says it’s great progress that tunnel excavation at Britomart can now proceed at full steam. “Aucklanders can look forward to having a modern rail network with better frequency and more stations.” CRL is scheduled to be completed in 2024.