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Town Hall Station Metro Tunnel Project
The $13.4B Metro Tunnel Project is one of the centerpieces of the Victorian Government’s Big Build agenda. Located 27m beneath Swanston Street – between Flinders and Collins Streets – Town Hall Station connects with nearby Flinders Street Station, giving commuters a convenient interchange between Metro Tunnel and City Loop services. It also improves passenger and public access to Federation Square, the revamped City Square and CBD landmarks.
The Role of A.G. Coombs
In addition to the construction of mechanical services and ventilation systems serving the station concourse, A.G. Coombs was responsible for the installation of the Over-Track Exhaust (OTE) system and specialist rail tunnel fan units capable of exhausting 200,000l/s of air when operational. The team leveraged its extensive experience garnered working on Sydney’s underground Metro stations.
Challenges
- Rail tunnel ventilation systems and critical systems are very specialised and nuanced.
- Construction sequencing working 27m underground required close coordination with other trades.
- The concourse’s 9m high cathedral-like vaulted ceiling brought significant risk associated with personnel working at heights.
- The number and diversity of critical underground spaces made fire mode planning complex.
- The high humidity environment needed to be factored into plant/equipment lifecycle.
- All plant had to be designed and installed in a duty/standby configuration to meet rail-specific requirements.
Approach & Methodology
- To meet rail-specific requirements, A.G. Coombs prefabricated duty/standby fans and coil arrangements with motorised dampers and valve sets making site installation significantly more straightforward.
- Fire mode was workshopped collaboratively with the Cross Yarra Partnership (CYP) consortium and contractors working on the other CBD underground station. It was essential to develop a holistic solution that was both achievable and consistent across both sites.
- Heavy-weight specification of 6mm plate steel superstructure, including transition pieces and attenuator connections, required specialist steel prefabrication techniques. These large and heavy pieces were designed and constructed into four quadrants before being lifted and joined onsite.
- Pipework modules that connect services from the Flinders Over-Station Development (OSD) plantroom to the 9m high concourse were also prefabricated to remove the working at heights risk during installation.
Key Outcomes
- The concourse, electrical and communications rooms are conditioned by a water-cooled chiller plant located within an OSD nearby. This plant serves chilled water fan coil units throughout, while a small boiler plant provides heating to retail spaces and back-of-house.
- High-level detail went into the designn lifecycle of plant and equipment to operate in a high humidity environment, with consideration given to specialist equipment design life and corrosion prevention.
- In an innovative move, A.G. Coombs designed and commissioned the rail tunnel ventilation system to operate in unison with adjacent underground stations’ ventilation systems to supply or exhaust air through the expanse of the connected rail tunnel.
- In the event of a concourse fire, the Environmental Control System plenum that conditions the platform via supply air in normal operation
