The Melbourne Metro project represents a pivotal transformation for the city of Melbourne. It encompasses a nine kilometre tunnel beneath the CBD to connect the West and East, and its estimated cost is approximately $11 billion.

The Melbourne Metro serves as an economic stimulus and significantly contributes to employment opportunities in the vibrant capital of Victoria. Melbourne Metro will substantially enhance commuter capacity and trip frequency upon its completion. As of October 2023, BG&E has successfully delivered close to 200 work packages, including temporary works design and a range of other services. The major phases of this project were completed in 2022, marking a significant milestone in our commitment to contributing to the success of the Melbourne Metro.

Melbourne Metro – Town Hall Station

BG&E has been responsible for designing and documenting numerous significant packages of work to enable the excavation and construction of the Town Hall Station. We have undertaken works at all three of the access shaft sites, inside the station cavern and as part of the works to tie into Flinders Street Station.

Work packages included

• Assessment of the existing Federation Square structure for the temporary construction arrangement, including demolition of significant lateral stability elements and replacement with temporary propping, to enable the construction of an access shaft into the station cavern. BG&E also undertook construction staging analysis to optimise the build out of the main Federation Square shaft in conjunction with the adjacent secondary shaft, which will hold the escalators.
• Temporary retention walls and strutting of a 40-metre-long and 5.6-metre-wide trench in the roadway of Flinders Street were required to construct a permanent reinforced concrete pedestrian tunnel linking the station cavern with Flinders Street Station. Maintaining these temporary supports throughout various stages of the construction process through coordination with other stakeholders and carefully staged construction sequencing.
• Two tower crane gantries are sitting over the public footpath on Swanston Street to enable the removal of the temporary shed and heavy deck at the City Square shaft and the construction of the permanent structure. Crane foundations were constrained on one side by the station works and on the other by numerous services running below the footpath and roadway, requiring close coordination with the construction team, Melbourne City Council and the asset owners.
• A large platform spanning over the City Square access shaft, which supported ventilation and scrubber units to ensure clean, fresh air for the teams working in the tunnel. Space constraints from the shaft retention system resulted in the deck having a unique doubly hung arrangement, with the primary beams hanging down from the capping beam on each side of the shaft and the secondary beams hanging from the primaries. This arrangement required the exploration of custom sections, connection detailing with the Client and steel shop detailer, and construction and demolition sequencing.
• Construction staging analysis of the top-down construction at the Flinders Over Site Development (OSD) site to fast-track completion of the substation to allow trains to start running through the tunnel for testing – a key milestone for the project. The assessment also optimised the sequence for removing the temporary plunge columns, which supported the station’s upper floors until the columns and liner wall had been completed.
• Temporary shafts in each of the platforms of Flinders Street station to access the construction of lift shafts running from the platform level to the underpass below. These works have ensured DDA access between the platforms of Town Hall and Flinders Street Stations. Each shaft was tightly constrained by the heritage listed platform structures, which remained operational throughout and were further complicated by highly adverse ground conditions.
• Construction sequencing and loading assessments of each concourse slab within the station cavern at Town Hall and State Library Stations to avoid temporary propping of these slabs, allowing train testing to start while construction continued. The construction team’s requirements for these slabs were highly dynamic, but BG&E’s responsive and engaged team ensured the construction programme remained on track.

Melbourne Metro – State Library Station

Construction of the new State Library Station was highly complex, with five separate access shafts and the station cavern sitting under Swanston Street.

Construction sequencing between the main rail tunnel and the adjacent station box was such that the tunnel boring machines for the main tunnels would pass the station box before its construction.

For safety reasons, a connecting adit between the tunnels and station box needed to be completed prior to the TBM’s passage. A 26 metre deep ‘D’ shaped temporary shaft was constructed to enable the adit’s construction. The temporary shaft, designed by BG&E, was constructed using concrete soldier piles and shotcrete infill panels, with a top capping beam and intermediate ring beams to provide lateral support to the piles.

Control of settlement and ground movement was a key design constraint to protect adjacent tall buildings and other surrounding infrastructure. Strain gauges and other monitoring devices were installed to provide real time feedback of actual movements with alarm states activated if detected movements exceeded predicted movements. Once the audit was completed, the shaft was backfilled and progressively demolished as the permanent shaft was excavated within which it sits.

Other Melbourne Metro Sites

BG&E’s participation in the Melbourne Metro Temporary Works project extended to all the metro sites, including

• Steel bumper beams at Arden Station to prevent impact from being precast concrete arch pieces and the adjacent completed structure during arch installation.
• Brackets to support the large, temporary steel struts and walers retaining the walls of various shafts, including at Parkville. BG&E’s proposed connection details incorporated allowances for construction tolerances – such as piles installed out of position and allowing these brackets to be fixed to the shotcrete wall instead of the piles to avoid clashing with heavy reinforcement within the piles.
• Polymer fibre reinforced shotcrete infill walls spanning between the shaft piles, where the rock was of good quality to remove the requirement for steel mesh reinforcement, allowing faster excavation.
• Steel-framed concrete hoppers and concrete pipe restraints at Anzac Station and the Eastern Portal sites, to allow improved delivery of concrete from street level to the base of the shafts.