Fig 1. Progress of four TBMs on the Melbourne Metro drives

Four Herrenknecht Mixshield TBMs and a fleet of roadheaders are completing excavations of the five underground stations and 9km of twin tube alignment for the new metro tunnel in Melbourne. Trinocular caverns create the mined stations at State Library and Town Hall, with cut-and-cover excavations at Arden, Parkville and ANZAC Stations. The four TBMs have completed more than 85% of the twin tube headings with all now into their final drives to Town Hall (Fig 1).

Cross Yarra Partnership, the design-build-finance concession comprising Lendlease Engineering, John Holland, Bouygues Construction and Capella Capital completing the AUS$6 billion PPP contract with Melbourne Metro Rail Authority, began work in 2018 at the Arden Station site. Early works were managed by John Holland and the first of the TBMs launched from Arden Station in September 2019.

Fig 2. Trinocular cavern of State Library and Town Hall Stations

State Library Station cavern as at December 2020

The trinocular caverns at State Library and Town Hall create an open space that allows the concourse and platforms to be integrated on a single level. The single cavern has three vaulted ceilings and a combined face area of 390m² (Fig 2). The total platform width at the two stations will be about 19m, some of the widest underground stations in the world, according to Melbourne Metro.

Roadheaders advanced cavern excavation in controlled increments with temporary shotcrete and rock bolts used as primary support. Sequencing the excavations was a complex task involving concurrent excavation and installation of the permanent lining with permanent invert slabs and station columns completed for load distribution before the outside platform caverns were excavated.

The segmentally lined running tunnels have been undertaken in two sections with two TBMs launching for drives either side of the Arden Station box site and two for drives either side of the ANZAC Station box site, all four machines heading to final breakthroughs at Town Hall Station (Fig 1).

Excavation of the 1.2km drives from Arden Station to the Kensington portal began in 2019 and broke through in February and March 2020. The shields were retrieved and returned by road to the Arden working site for reattaching to the gantries, which were backed up through the completed drive and relaunched east on the 1.4km drives to Parkville Station in May and June 2020. They arrived in August and September 2020, transferred across the open station box and relaunched through the end wall to complete the 1km drives to State Library Station in October and November 2020.

TBM cutterhead at ANZAC Station

From Parkview the alignment dives deeper to State Library Station to avoid existing infrastructure under the city centre (Fig 2). The first TBM broke through at State Library in December 2020 and was relaunched in February to drive to its final destination at Town Hall. The second machine broke through in February 2021 and relaunched in April 2021.

In the south, the two TBMs launched from the ANZAC Station box in April and May 2020, driving 1.7km to the South Yarra shaft for breakthrough in September and October 2020. The machines relaunched from ANZAC in December 2020 and January 2021 to complete the 1.8km drives to Town Hall, including a 12m underpass of the Yarra River.

Running tunnel segments are produced at a facility in Deer Park, west of Melbourne. The six segments per ring are transported to the TBMs by multi-service vehicles.

Fig 3. Metro alignment as part of new airport link

Two cut-and-cover dive structures provide transition of the underground alignment with surface rail infrastructure and are being completed by a consortium of John Holland, CPB Contractors and AECOM, which is also responsible for reconfiguring existing lines to link with the new infrastructure. The portal at South Yarra was completed five months ahead of schedule in March 2021. A section of the South Yarra TBM reception shaft has also been demolished to connect the portal structure to the twin tubes. Rail systems will be installed by CPB Contractors and Bombardier Transportation.

Construction of the project is on track to complete in 2025, a year ahead of the original schedule. At that time, the Sunbury, Cranbourne and Pakenham line services will transfer to the underground alignments, removing them from the City Loop tracks and allowing other routes to run additional services. The new infrastructure will also form an integral part of plans to link Melbourne Airport to the city rail network with services running to the city centre in less than 30 minutes. Provisional plans indicate the link will run on a combination of surface and elevated tracks from the airport before running underground through the new metro line and connecting onto Cranbourne and Pakenham in the southeast of the city (Fig 3).

Gallery

Arden Station construction in October 2020

Parkville Station box in November 2020

Roadheaders completed most of the underground station excavations

Completed portal structure at South Yarra

The first section of the Metro Tunnel in Melbourne, Australia, is now complete. The first TBM, a 7.2m diameter Herrenknecht Mixshield, broke through into a 13m deep shaft at Childers Street, Kensington on 23 February 2020.

First section of Melbourne Metro Tunnel complete

Since its launch in September 2019, the TBM has travelled 1.2km from Arden Station to the western tunnel portal at Kensington – under rail lines, CityLink, Moonee Ponds Creek, North Yarra Main Sewer and the West Melbourne Terminal Station. Due to being so close to the rail corridor and the ground conditions in the area, a reception seal was used and the shaft was flooded with water for the breakthrough, to maintain the pressure supporting the ground around the TBM.

The TBM has installed 4,200 curved concrete segments to create 700 rings lining the walls of the tunnel. The segments, each weighing 4.5 tonne, are among 56,000 being manufactured at a purpose-built concrete manufacturing plant in the Melbourne suburb of Deer Park.

The TBM is one of four Herrenknecht machines of the same type and diameter to be used on the project. The second TBM is travelling on a parallel route to excavate the second tunnel from Arden to Kensington, and will break through in the coming weeks. Work began in January 2020 at the site of the new Anzac Station on the St Kilda Road site to assemble the third and fourth TBMs for the project. These are expected to be launched in mid-2020 and will break through at a 19.5m retrieval shaft at the eastern tunnel portal in South Yarra.

When complete, the Metro Tunnel will create capacity for more than a half a million extra passengers a week during peak times across the Melbourne train network.

Tunnelling has now commenced on the North Melbourne to Kensington section of the Melbourne Metro in Victoria, Australia. The PPP project, awarded to the Cross Yarra Partnership of Lendlease Engineering/John Holland/ Buoygues Construction and Capella Capital, will deliver a 9km twin-tube link from Kensington to South Yarra as part of a new end-to-end rail line from Sunbury in the west to Cranbourne/Pakenham in the south east with five new underground stations at North Melbourne, Parkville, State Library, Town Hall and Anzac (Fig 1).

First TBM being assembled

Two 7.2m diameter Herrenknecht Mixshield TBMs were assembled at the new North Melbourne Station site in mid-2019 and were launched separately in October and November 2019. The first TBM has progressed more than 250m to date, while the second has progressed about 50m. They are expected to reach the western tunnel portal at Kensington in early 2020 before being transported back to the launch site in North Melbourne where they will relaunch towards Parkville and the city center.

A further two TBMs will be launched in 2020 from the future Anzac Station in the Domain Precinct and advance towards South Yarra from where they will be transported back to the Domain work site to be reassembled in the station box to start their journey towards the central business district (CBD) and under the Yarra River.

Fig 1. Melbourne Metro extension alignment

The AU$6 billion metro project will free up space in the current City Loop subway and rail system by taking three of the busiest train lines in the city out of the Loop and running them through the new underground route, creating space for more trains, more often across the network.

Along its route, the new metro line will be up to 40m deep (Fig 2). The deepest point will be under Swanston Street, at the northern edge of the CBD, where the new tunnels pass under the existing city loop tunnels. From the station under Swanston Street at Flinders Street, the underground alignment runs under below the Yarra River before passing under the CityLink highway on its way to the new Anzac Station under St Kilda Road.

Fig 2. Station depths and TBM routes

To keep Swanston Street open while the new link is built, working access shafts are being excavated adjacent to where station entrances will be. These working shafts will transport machinery, equipment and workers underground to excavate the station caverns. Disruption on the surface will be greatly reduced, and trams will continue to travel along Swanston Street during construction.

The State Library and Town Hall stations will be built as trinocular caverns. Three overlapping tunnels will be excavated by roadheaders to create a wide open space that allows the concourse and platforms to be integrated on a single level, rather than two tunnels separated by a cross passage. The new North Melbourne, Parkville and Anzac Stations and entrances will be built by cut-and-cover.

The geology of the area is variable and includes soft soils, including Coode Island Silt, and hard basalts under the Yarra River and in some sections of the western alignment. Many sections of the tunnel alignment feature a mixed-face geology.