Tunnelling stages

North Melbourne to Kensington

In mid-2019, 2 tunnel boring machines (TBMs) were assembled at the Arden Station site and launched separately to tunnel towards the western tunnel entrance at Kensington.

Before the TBM’s cutterhead 'broke through' into the retrieval shaft, the shaft was filled with water to balance groundwater levels while the TBM constructed the final section of tunnel. In February 2020, the first TBM, Joan, arrived in Kensington and the second TBM, Meg, arrived in March. The water was then drained and the TBM retrieved. Water was then pumped back to the water treatment plant at Arden Station site via the TBM.

The rear (gantry) sections of the TBMs travelled back to Arden Station through the constructed tunnel, and the rest of the oversized pieces were transported back at night by truck. The TBMs were then relaunched towards Parkville.

North Melbourne to Parkville

In mid-May 2020, TBM Joan launched from the Arden Station site to tunnel towards Parkville, followed by TBM Meg in June. Joan broke through at the Parkville Station site in late August, while Meg arrived in September 2020.

The TBMs were transferred on steel rails with hydraulic ramps through the station box. Two launch frames were set up at the eastern end of the station box to assist the TBMs in breaking through a ‘soft eye’ (reinforced with fibreglass rather than steel) to begin tunnelling again towards the CBD.

Parkville to State Library

TBM Joan relaunched in October 2020 to begin tunnelling the 1km stretch from Parkville to the new State Library Station site. TBM Meg followed in November 2020 to tunnel the parallel route.

TBM Joan broke through at the State Library Station site in December 2020. TBM Meg broke through at the State Library Station site in February 2021.

State Library to Town Hall

TBM Joan was relaunched in February to tunnel towards the Town Hall Station site. TBM Meg followed in March 2021 digging the parallel tunnel.

TBM Joan broke through at Town Hall station in April 2021, with Meg following shortly after in May 2021. Meg's breakthrough marks the conclusion of tunnelling for the Metro Tunnel.

Domain precinct to South Yarra

At the site of Anzac Station, TBMs Millie and Alice were assembled in the station box and launched separately to tunnel towards the new tunnel entrance at South Yarra. Millie was launched in April 2020, with Alice following in May.

TBM Millie arrived at South Yarra in September 2020, while TBM Alice broke through in October.

Domain precinct to CBD

The TBMs were reassembled at the site of Anzac Station to complete the tunnel towards the CBD and under the Yarra River. TBM Millie was launched towards the CBD in December 2020 and Alice was launched in January 2021.

TBM Millie successfully tunnelled under the Yarra, breaking through at Town Hall Station in late March 2021 with Alice following in May 2021. These milestones marked the completion of tunnelling for Millie and Alice.

Tunnelling milestones

2021

• May 2021 – Meg breakthrough at Town Hall Station, final tunnel complete
• May 2021 – Alice breakthrough at Town Hall Station
• April 2021 – Joan breakthrough at Town Hall station
• March 2021 – Millie breakthrough at Town Hall station
• March 2021 – Meg relaunched towards Town Hall Station
• February 2021 – Meg breakthrough at State Library Station
• February 2021 – Joan relaunched towards Town Hall Station
• January 2021 – Alice relaunched towards Town Hall Station

2020

• December 2020 – Joan breakthrough at State Library Station
• December 2020 – Millie relaunched towards Town Hall Station
• November 2020 – Meg relaunched towards State Library Station
• October 2020 – Joan relaunched towards State Library
• October 2020 – Alice breakthrough at South Yarra
• September 2020 – Meg breakthrough at Parkville
• September 2020 – Millie breakthrough at South Yarra
• August 2020 – Joan breakthrough at Parkville
• June 2020 – Meg relaunched towards Parkville
• May 2020 – Joan relaunched towards Parkville
• May 2020 – Alice launched towards South Yarra
• April 2020 – Millie launched towards South Yarra
• March 2020 – Meg breakthrough at Kensington
• February 2020 – Joan breakthrough at Kensington

2019

• October 2019 – Meg launched towards Kensington
• September 2019 – Joan launched towards Kensington