by India Murphy, Journalist, Infrastructure magazine
The Metro Tunnel is the biggest public transport project in Victoria’s history and is anticipated to be completed by 2025. With new rail tunnels being built under the city, temporary noise and vibration caused by construction is a potential concern for residents, businesses and others in this busy urban environment. Here’s how the project is working to mitigate construction impacts.
The Metro Tunnel Project involves the construction of five new underground rail stations and twin 9km tunnels that link the city’s south-east to the west, and major excavation works are well underway.
The new end-to-end rail line will run from Cranbourne/Pakenham in the south-east to Sunbury in the west. The project will ease congestion in the heart of the rail network by freeing up space in the City Loop with high–capacity trains and five new underground stations at North Melbourne, Parkville, State Library, Town Hall and Anzac.
Project currently on track
Two of the four massive tunnel boring machines (TBMs) which will build the twin 9km tunnels have arrived in Melbourne and will soon be prepared for launch from the new North Melbourne Station construction site in Arden later this year.
The machines will head towards the western tunnel entrance in Kensington. Once they have reached Kensington, the cutterheads and shields will be dismantled and trucked back to their starting point, to be reassembled and then launched towards Parkville and the CBD.
Excavation of the station box is underway in Parkville, with a temporary deck being installed over the work site to minimise noise and dust impacts while excavation is carried out underneath.
Three road header machines are currently excavating deep under the northern end of Swanston Street where the new State Library Station will be located. These machines have a rotating cutterhead that can cut through rock three times harder than concrete.
A total of seven road headers will be used to construct the stations in the CBD — four for State Library Station and three to build Town Hall Station, at the southern end of Swanston Street.
At Federation Square, one of three entrances to the future Town Hall Station, piling is underway ahead of excavation. An acoustic shed, one of six to be used across the project, will be constructed over the site to minimise noise and dust impacts.
An acoustic shed is also planned for the Anzac Station site on St Kilda Road. The area will serve as the launching site for the remaining two TBMs which will head towards South Yarra, where major works to build the eastern tunnel entrance are underway following two major construction blitzes.
Problem-solving strategies
As it is being built in the heart of Melbourne’s CBD, managing the impacts of noise and vibration from construction is one of the biggest challenges facing this massive infrastructure project.
Making special considerations to reduce noise and air pollution is critical in areas such as Parkville, as several hospitals and research institutions located there use highly specialised equipment which could be affected by vibration and dust.
Due to the sensitive nature of work carried out by the hospitals, and in particular researchers at the University of Melbourne, these potential problems require a tailored management approach.
The Metro Tunnel Project is working closely with the neighbouring institutions in the precinct to identify ways to mitigate the impacts of construction.
As part of the robust Environment Effects Statement process and construction planning, all Metro Tunnel sites were rigorously assessed for noise and vibration impacts.
Rail Projects Victoria (RPV) spokesperson Michael Scanlan said, “We’ve been working with councils, hospitals, universities, businesses, residents and other relevant stakeholders since 2015 to ensure any concerns are addressed as early as possible.
“The Metro Tunnel Project contractors build on this work by undertaking their own analysis of potential impacts from construction, including noise and vibration, and are implementing appropriate mitigation measures.”
Extensive piling in Parkville for the station box — successfully completed in 2018 — used cutting–edge technology to break back the piles to reduce noise, vibration and air quality impacts.
The method involved the use of expanding mortar to create pressure and generate a perfectly horizontal cut, so the top layer of concrete can be easily removed by a crane. This phase of work normally requires excavators and jack hammers to break back the ‘head’ or top section of the pile.
To further reduce disruptive noise and vibration, industry best practice measures such as acoustic sheds, noise walls and blankets are in place on Metro Tunnel construction sites.
Cooperating with the community
Rail Projects Victoria acknowledges that a project of the scale and complexity of the Metro Tunnel Project will create some unavoidable disruption while it is being built, so an extensive and robust public planning and stakeholder engagement process was undertaken to understand, mitigate and manage impacts.
“We are working with affected businesses and residents to manage impacts and provide practical support,” Mr Scanlan said.
Environmental Performance Requirements (EPRs), developed as part of the public Environment Effects Statement planning process, require noise and vibration levels to be monitored and appropriately mitigated.
“Should Metro Tunnel construction noise exceed noise guidelines set out in the relevant EPRs, our construction contractors work with affected residents and offer respite measures.
“We will continue to work closely with residents, businesses, commuters and others affected by construction impacts as we get on with delivering the critically-needed rail infrastructure.”
In addition, noise and vibration monitors are installed on all sites. Modelling and monitoring of potential construction impacts is undertaken throughout construction to inform on–site mitigation measures and ensure all site activities are within the EPRs.
Property condition surveys of heritage listed buildings and other residential and commercial properties are also undertaken prior to Metro Tunnel works starting nearby to understand building conditions and inform construction methodology.
These surveys provide a reference should a property owner believe their property has been adversely affected by construction works and assists in resolving any issues further down the track.
Five Community Reference Groups (CRGs) have been established by RPV to consult with residents, businesses and other stakeholders in proximity to the future tunnels, underground stations and tunnel entrances, and manage issues within these areas.
“These reference groups further strengthen the consultation and engagement framework for the delivery of the Metro Tunnel Project,” Mr Scanlan said.
“Regular engagement with local residents and businesses has enabled the project to inform the community of any changes to construction activities and manage expectations surrounding noise and vibration impacts.”
Metro Tunnel operations
The project’s contractors are required to design and construct the tunnels in accordance with stringent environmental performance requirements for noise and vibration once the Metro Tunnel is operational.
The contractor also has a 25-year maintenance contract to maintain the tunnel structures.
Before the Metro Tunnel is fully operational, it will undergo an extensive testing and commissioning phase of up to two years. This process will verify the design and determine if any additional mitigation measures are required to address noise and vibration. The tunnels are being designed to accommodate any such measures.
Lessons learnt globally
The Metro Tunnel Project is fortunate to benefit from a significant number of experts with overseas experience within the project team, who can draw on their work on rail projects all over the globe including Singapore, the UK, Hong Kong, India and Taiwan.
“Attracting this world–class experience to Victoria is not only shaping the Metro Tunnel but is helping to upskill the next generation of local rail experts to deliver future projects in Australia,” Mr Scanlan said.
Full speed ahead
The project team will continue to implement any practical measures available to reduce the unavoidable noise and vibration caused by construction.
Acoustic sheds, noise walls and blankets, as well as technology to break back the piles will continue to be used to mitigate noise and dust.
“The Metro Tunnel Project is a major step towards transforming Melbourne’s rail network into an international-style ‘turn up and go’ metro system and is scheduled to open in 2025, a year ahead of schedule,” Mr Scanlan said.
