Building the CBD stations
The construction of the two new stations under Swanston Street in the heart of the city presents a range of engineering and construction challenges.
- Navigating existing below-ground infrastructure, such as water, gas and electricity services and the City Loop.
- Managing the effects on vehicle, pedestrian, cyclist and tram movements.
- Minimising disruption to residents, traders and businesses.
- Maintaining a safe environment for the project workforce and the community.
Station construction techniques
To keep Swanston Street open and trams running while the Metro Tunnel is built, access shafts up to 11 storeys deep are being dug adjacent to Swanston Street at City Square, Franklin Street, A'Beckett Street and behind Young and Jackson Hotel.
These shafts will be used to transport machinery, equipment and workers underground. Equipment is then used to excavate and line the stations below the surface of Swanston Street.
This construction approach minimises disruption at surface level and is commonly used overseas, particularly in constrained city environments. The above ground disruption to businesses, cyclists, pedestrians and surrounding streets is greatly reduced as a result.
Tunnelling under the CBD
While tunnel boring machines are being used to build most of the Metro Tunnel, a different method of tunnelling will be used beneath Swanston Street between the two CBD stations.
Due to ground conditions and the number of building basements and foundations in the area, a mined tunnel will see the use of road header machines to excavate the tunnels and station caverns. These machines have a rotating cutter head that is mounted on a boom. After the road headers carve out the tunnel, it is reinforced with a combination of sprayed concrete, rock bolts and a final concrete liner. The stations will be built as 'trinocular' caverns to suit the complex underground conditions.
Three overlapping tunnels will be mined by the road headers to create wide platforms with supporting columns and vaulted ceilings. The total platform width will be around 19 metres – one of the widest metro platforms in the world.
Parts of Franklin Street between Elizabeth Street and Victoria Street have been temporarily closed to support construction, along with part of A'Beckett Street. A site near the corner of La Trobe Street and Swanston Street will also be utilised for construction and ultimately be the site of a new station entrance.
City Square has been temporarily occupied to create an access shaft, and will ultimately become a station entrance. In addition, there will be a construction site facing onto both Swanston Street and Flinders Street (around, but not including, the Young and Jackson Hotel). Another construction site will be located at the station's Federation Square entrance at its northwest corner. See the Town Hall Construction Update page for details of current works at these locations.
Key construction activities
Construction activities within the CBD will include:
- Preparatory works including tree removal and protection, and the relocation of underground services such as water, electricity, gas, sewers, stormwater and telecommunications.
- Excavation of construction access shafts.
- Demolition of buildings at station entrance locations, where required.
- Excavation of the tunnel between the two CBD stations.
- Structural works and station entrance connections.
- Architectural, mechanical and electrical fit-out.
- Track works and the installation of signalling, safety and communications systems.
- Site remediation, including landscaping at Swanston Street, City Square and Federation Square.
Temporary acoustic sheds up to 20 metres high will enclose some of Metro Tunnel's CBD construction sites at City Square, Franklin Street and A'Beckett Street.
Traffic and transport
The use of mined tunnelling and underground excavation techniques will significantly reduce impacts on Melbourne's CBD, helping to ensure tens of thousands of workers, residents and visitors can continue to access Swanston Street while construction of the new tunnels and stations continues underground.
However, there will still be some unavoidable disruption at surface level and some changes to roads, tram services, and bicycle and pedestrian access will be required to deliver the project.
State Library Station
Building the State Library Station requires the temporary closure of Franklin Street between Swanston Street and Bowen Street.
Other traffic changes at the northern end of the CBD include the permanent closure of A'Beckett Street to vehicle traffic at Swanston Street, and reduction in the number of traffic lanes on Franklin Street between Swanston Street and Elizabeth Street.
See the CBD (north) traffic changes page for more information.
Town Hall Station
At the southern end of the CBD, short-term partial closures of Flinders Street will be required to construct the underground pedestrian connections linking Flinders Street Station and Federation Square to Town Hall Station. These works may temporarily impact traffic, trams and footpaths.
See the CBD (south) traffic changes page for more information.
Public transport, cycling and walking
Tram services will continue to run during the Metro Tunnel's construction in the CBD, although some activities are likely to temporarily impact tram services along Swanston, Flinders, Collins and La Trobe streets. Construction activities in the CBD will be carefully managed to minimise disruption to pedestrians and cyclists, especially during peak periods.
Pedestrian and bicycle paths will be maintained around construction sites, and will include arrangements to direct pedestrians and cyclists safely around work areas.
Construction traffic routes for the CBD aim to move trucks and other construction traffic away from the city as quickly as possible, using major arterial roads such as Victoria Street, Wurundjeri Way, Dudley Street and the Exhibition Street extension.
The impacts of additional traffic will be managed by using detailed traffic management plans. These plans will seek to minimise truck movements during peak periods, manage truck arrivals and departures to avoid trucks queuing in CBD streets, and minimise truck movements past residential areas at night time.
Construction of the two stations and the tunnels under Swanston Street will take around five years to complete.