Mary Searle Bell looks at a redevelopment project of an old area of the Queen city that started in 2011 and won’t be completed until 2030.
WYNYARD QUARTER on Auckland’s waterfront has been transformed over recent years. The industrial and marine heritage of this part of the city is now rubbing shoulders with many and varied restaurants, office blocks and upscale apartments and townhouses, as well as the other trappings of inner city life.
This inner city area had been progressively developed by the Auckland Harbour Board to provide additional berthage capacity and flat land for port related activities. From the 1930’s it started to be used for bulk petro-chemical storage, leading to the area becoming known as the Tank Farm.
Changes to the way fuel was supplied to Auckland meant much of the land was no longer required for fuel storage, freeing it up for revitalisation. In 2005, a vision was developed to transform the area in stages over 25 years.
In August 2011, stage one opened made up of $120 million of capital projects. When Wynyard Quarter is fully developed in 2030, it will be home to around 3000 residents as well as 25,000 workers.
Along with the new buildings, the streets are getting a facelift. But it isn’t just what is on the surface that counts. Much of the work is happening below ground.
New piping and landscape design improve the stormwater before it flows into the harbour, and the wastewater network is getting an upgrade so that it can support the increased population forecast for the area.
Watercare awarded the construction of a new $16 million wastewater pump station and rising main under separate contracts: the pump station to Fulton Hogan and the rising main to Hawkins (now Downer).
Work on the rising main began along with street upgrades in early 2015, and on the pump station in December 2016. The project was due to finish at the end of May 2018.
Peter Kukulsky, project engineer at Watercare, says the 800,000 litre tank has been constructed using the secant piling method. This helped combat the difficulties posed by high ground water levels.
“Sixty two interlocking male and female piles were drilled down to bedrock 20 metres below the ground level. Concrete for the piles was poured progressively – 45MPa for male and 8Mpa for female piles,” he explains.
“A ring beam was poured to connect the piles at the top. Earth was then excavated out from within the piles.”
Peter says the total volume of excavated earth from the tank area was approximately 1200 cubic metres, plus a further 400 cubic metres from the ancillary chambers area (valve, flowmeter and odour control unit chambers).
“The soil within the site is contaminated (mainly hydrocarbons) – the legacy of the previous occupants. This meant any earth being carted off site had to be taken to special waste disposal site and additional personal protective equipment had to be worn by workers when handling the soil.
“We also installed a sprinkler system around the entire site perimeter to prevent any odours leaving the site.”
A 200mm layer of shotcrete was applied on the tank walls in three stages as the excavation progressed. Then a two-metre-thick base was constructed to ensure the structure doesn’t float.
Peter says, to install the inlet pipe for the tank, the contractor had to make an opening through the secant piles and thrust a steel casing towards the inlet manhole in Pakenham Street.
“Ground water was expected, however, the inflow was 10 times higher than expected and completely flooded the tank. It took two months to stop the ingress and pump the water down.
“Fulton Hogan came up with the method of injecting an inert chemical compound around the outside of the structure to seal it.”
Peter says an activated carbon odour control unit, housed in underground chamber, will treat any odours from the pump station.
Above ground, a control building has been constructed – its 10.5-metre-high curved walls reflect the nearby silo stacks.
It sits in what will be landscaped into a small neighbourhood park.
This small ‘pocket park’ will be constructed by Auckland Transport once the pump station project is complete.
The pump station pipework connects onto a 720 metre long rising main installed by Downer under three separate contracts. The rising main discharges into the Orakei Main Sewer on Victoria Street West.
Within the Wynyard Quarter itself, the new pipeline has been laid by open trenching in ground that had been stabilised by IMS (In-situ Mass Stabilisation).
Pieter Maarschalk, who was project manager with Watercare until recently, explains that IMS is a technique where cement is mixed into the ground using specialised machinery to create, in effect, a weak concrete that enables trenching to be done in poor quality ground that would otherwise need sheet piling or similar for support.
“The ‘poor quality’ here was due to it being reclaimed land with a very high and tidally-influenced water table,” he says.
“There were, nevertheless, a couple of places within Wynyard Quarter where IMS did not work particularly well, due either to proximity to existing services – where it was physically impossible to get the mixing head in – or where the trench got down into the underlying Puketoka formation, which the equipment could not penetrate.
“In two sections this was overcome by sheetpiling and in another a short timber heading was driven under existing services.”
Outside Wynyard Quarter, the section in Halsey Street, between Fanshawe and Victoria Streets, was laid by open trenching. Pieter says the main challenge here was traffic management.
For the crossing of Victoria Street West, to minimise the road width closed by excavation at any one time, an oversize (525mm) duct of concrete pipes was laid during a December-January low traffic period and the polyethylene service pipe pulled in afterwards.
“A ring beam was poured to connect the piles at the top.
Earth was then excavated out from within the piles.”
The same method was attempted to cross Fanshawe Street. Pieter says it was successful for part of the way under the eastbound lanes but could not be used under the west-bound lanes due to traffic management considerations.
“Due to underground obstructions such as an old sea wall under the eastbound lanes, in one part it turned out to be more practicable to lay the PE pipe by direct trenching rather than in a concrete duct.
“Under the westbound lanes, where the road could not be even partially closed, a 1300mm concrete sleeve was installed by pipe-jacking and the PE pipe laid inside.
“To support the PE pipe and achieve the required grade, a 525mm uPVC duct was first secured inside the 1300mm pipe, and then the PE pipe was pulled in.”
An additional challenge under Fanshawe Street was to safely tunnel under two 220kV cable clusters belonging to Transpower.
Traffic management was a significant challenge to this project. Within the Wynyard Quarter, the pipeline was laid as part of road upgrade projects and the roads were completely closed.
“In Halsey Street south of Fanshawe, traffic restrictions had to be imposed for several months. Prior to this, extensive traffic modelling was carried out, against the backdrop of other projects going on at the time, to find a solution that would be least disruptive to local businesses and commuters.
“The plan included temporary changes to some bus routes,” explains Pieter.
“Commuters adapted, but it did make life difficult for the businesses and we were grateful for their patience and understanding.
“We were also grateful for the ongoing support and cooperation from Auckland Transport’s traffic operations and AT Metro.”
Peter credits the project’s success to having really good teams from Fulton Hogan and Downer.
He also says the collaboration between the three council-owned organisations involved – Watercare, Panuku Development Auckland, and Auckland Transport – has resulted in an; “unusual and cool building which will enhance the surrounding urban environment”.
“People using the park will quite likely not even realise that there is an underground wastewater pump station under their feet.”
This article was first published in the July 2018 issue of NZ Contractor Magazine.