TWO boring machines would set off from Little Hartley near Lithgow to dig twin Great Western Highway tunnels to Blackheath, according to new NSW Government documents now on public exhibition.
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The documents also estimate the twin tunnels project would support a peak construction workforce of up to 1100 full-time jobs, work would start in 2024 and traffic would be navigating its way underneath Mount Victoria and Blackheath by 2030.
The NSW Government might still be short of Commonwealth money for the twin tunnels - part of the proposed wider upgrade of the highway from Lithgow to Katoomba - but it has gone ahead regardless with the release of an environmental impact statement (EIS) for the ambitious project.
While there have been periodic announcements in recent years about taking that section of the highway underground (including that it will be toll-free), the EIS provides much more detail about how the government imagines the mechanics of the project would work.
According to the EIS, tunnel boring machines (similar to those being used on the Sydney Metro rail project) have been identified "as the preferred tunnelling methodology for the mainline tunnels as they can excavate at a faster rate than roadheaders and are able to install precast structural, waterproof tunnel lining progressively as they tunnel".
"The selection of the TBM tunnel construction method would ensure that tunnel construction is sensitive to the unique environmental and cultural surroundings of the Blue Mountains," the EIS says.
"It would also provide a value for money and sustainable construction method, given the precast tunnel lining would add to the tunnel's longevity."
Using two TBMs launched from Little Hartley has been identified as the preferred option "to minimise impacts at the eastern [Blackheath] portion of the project", as well as reducing the demand for labour and construction materials during the course of the tunnel construction (as opposed to having four TBMs running).
The project, according to the EIS, would comprise twin tunnels around 11 kilometres long connecting to the Great Western Highway at Blackheath and at Little Hartley.
Each tunnel would accommodate two lanes of traffic, the speed limit within each tunnel would be 80 kilometres per hour and each tunnel would have a carriageway width of around 10.5 metres (including two traffic lanes and shoulders) and a height clearance for vehicles of around 5.3 metres.
The tunnels, according to the EIS, would be designed to accommodate heavy vehicles including service and freight vehicles and there would be a vehicle cross-passage between the tunnels for emergency service vehicles to switch between the westbound and eastbound tunnels around the tunnel mid-point.
As well, pedestrian cross-passages would be provided at regular intervals around every 120 metres to allow for emergency pedestrian egress if an incident occured in one of the tunnels.
The EIS says construction of the twin tunnels project is expected to take around eight years.
"Subject to planning approval, construction is planned to commence in 2024 and continue until 2031. The project is expected to open to traffic by 2030," it says.
The EIS says the project is expected to support an indicative peak construction workforce of up to 1100 full-time equivalent jobs during the eight years of construction and the workforce would be primarily concentrated at the Little Hartley construction site.
Once the TBMs set off from Little Hartley, they would tunnel eastbound on an uphill gradient at an average rate of around 70 to 90 metres per week.
The EIS says the twin tunnels project "would reduce light vehicle travel times between Blackheath and Little Hartley by around nine minutes, and heavy vehicle travel times by around nine minutes during the weekday AM peak hour period".
The Commonwealth Government's $2 billion for the east and west sections (either side of the proposed tunnels) of the highway upgrade remains on hold while new Infrastructure Minister Catherine King says she wants to see the overall plan for the entire project.
NSW Farmers Association recently called for the state and federal governments to get their differences sorted out in regards to the project and get on with the highway upgrade.
