By Matt O'Sullivan
Thousands of tonnes of crushed rock from twin tunnels dug for a new metro line under Sydney Harbour and the central city will be moved by barge instead of truck in an attempt to allay residents' concerns about construction.
Councils and planners had warned that transporting massive amounts of spoil on trucks through city streets from Blues Point, at the tip of McMahons Point north of the harbour, and from Barangaroo in the south, would worsen road congestion.
In awarding a $2.8 billion contract for the 15.5-kilometre rail tunnels from Chatswood to Sydenham, Transport Minister Andrew Constance said the barging of spoil would reduce the number of truck movements in the city.
"Very pleasingly this is part of the arrangement that's been reached as part of this contract signing," he said.
Most of the proposed metro line is expected to run through tunnels.Credit: Geoff Jones
Residents and businesses at Blues Point will still have to bear a 2100-square-metre construction site near the waterfront, which will be used as an entry point for the tunnelling. The site is near Harry Seidler's well-known Blues Point Tower.
About 8000 tonnes of soil will be brought to the surface at Blues Point.
North Sydney mayor Jilly Gibson welcomed the removal of rock by barge, saying it would significantly lessen disruption for residents, local businesses and motorists.
While the use of barges might allay some fears, the NSW Port Authority has raised concerns about them impacting shipping channels on the harbour during construction.
Blues Point will be the location of a temporary construction site for the tunnelling.Credit: Jessica Hromas
The contract signed on Thursday is also for the excavation of six new underground stations, the demolition of buildings up to 22 storeys high and a crossover cavern at Barangaroo to allow trains to switch from one track to another.
Two of the companies in the winning consortium – CPB Contractors and John Holland – built 15-kilometre-long twin tunnels from Bella Vista in Sydney's north west to Epping as part of the first stage of the metro line.
Sydney Metro director Rodd Staples said the final destinations for the spoil was yet to be decided and was a "matter of detail the contractor would work out" over the coming year before the first boring machines started tunnelling at the end of 2018.
The spoil from the tunnels for the first stage of the new rail line, along which driverless trains will run, ended up at a range of locations, including development sites at Blacktown in Sydney's west.
Mr Staples said the second stage of the project was more challenging than the first because of the soft ground under Sydney Harbour and the need to navigate around building basements and other tunnels under the CBD.
"This is the most exciting but also the most challenging tunnelling project that this country has ever seen through the busiest CBD," he said.
The project team had spent the past few years mapping the area under the CBD, and surveying buildings. "We are very confident we know most of what's there," he said.
Five tunnel-boring machines - one of which is specialised to dig under the harbour - will churn through earth up to 58 metres below the surface. The tunnel contract is scheduled to be completed by 2021.
Demolition of buildings for the project has already begun at Victoria Cross in North Sydney and in the CBD at Castlereagh and Pitt streets, which has involved "soft strip outs" before so-called munching machines tear them down.
The government has put the cost of the second stage at between $11.5 billion and $12.5 billion. The first stage cost $8.3 billion.
An environmental impact statement for the final component of the second stage – conversion of the existing rail line between Sydenham and Bankstown to metro – is due in the second half of this year.