"By entering a project in an award which judges innovation, skill and the contribution of a structural engineer in improving the community, people and planet, it is an opportunity showcase your project and see how your peers view the skill and innovation your project. The standard of entry is very high and attracts an international field.
Winning the Supreme Award has meant a great deal both myself as well as the team involved in delivering this once In a career project."
Introduction
Sydney Metro is Australia’s biggest rail infrastructure investment and will revolutionise the way our community navigates the city. By 2030, Sydney will have four metro lines, with forty-six stations and 113 kilometres of standalone metro rail.
The Central Station Metro is a $955 million transformation at the heart of Sydney’s transport network and the most significant upgrade to Central Station in over a century. Delivered as part of Sydney Metro City & Southwest, the project inserts a new 230-metre-long metro station beneath existing platforms 13-15 within a 1906 heritage precinct all while the station remained fully operational for more than 270,000 daily commuters.
Often described as “open-heart surgery on Australia’s busiest railway interchange,” the project required excavation and construction of the Sydney Metro platforms 27m beneath existing platforms 13, 14, and 15, a new 19-metre wide Central Walk concourse from a new entrance on Chalmers Street, escalators directly to suburban platforms 16 – 23, and a revitalisation of the Grand and Northern Concourse (herein GNC) entrance on Eddy Avenue.
In 2018, the NSW Government awarded Laing O’Rourke (LOR) the contract to deliver the project in collaboration with Aurecon, GHD, Woods Bagot and John McAslan + Partners.
Aerial and Cross section view of Central Station Metro - Aurecon
Project Challenges
Before the project moved into delivery, the project team held a series of early “what-if” workshops to unpack the complexity of the site and explore alternatives to the reference design. These informal sessions where almost every idea began with “what if…?” or “could we…?” allowing the team to test possibilities without constraint and quickly revealed the scale of the engineering challenge.
The reference design relied on a traditional bottom-up construction sequence in which the full excavation had to be completed before any permanent structure could rise, with services and fit-out following well after. This sequence was inefficient, dependent on tunnel boring progress, and incompatible with the compressed program. Meanwhile, access constraints meant all materials could only move through a single entry point on the southern side, effectively requiring the team to build a complex underground station as if crafting a ship inside a glass bottle while the station remained fully operational. This approach saved approximately 9 months on the construction program.
Central Station therefore presented a combination of constraints rarely encountered on a single project:
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The station had to remain fully operational throughout all stages of construction, safely accommodating 270,000 daily commuters (pre-COVID).
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The design required seamless provision for future expansion and interchange integration
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Construction access was limited to a single entry point via the Sydney Yard Access Bridge.
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Live suburban, intercity, and freight rail lines operated directly above and adjacent to a 27-metre-deep excavation.
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The 120-year-old Devonshire Street Tunnel intersected the Metro Box footprint and needed to remain open throughout construction.
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Congested heritage and legacy service tunnels required precise digital mapping and diversions.
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Stress-sensitive sandstone geology demanded active ground-movement management.
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Possessions were restricted primarily to 3-hour nightly work periods, dictating construction methodology.
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A dense heritage setting, including structures from 1906, required careful preservation and integration.
These constraints demanded a design approach built on innovation, flexibility, real-time decision-making, and an intimate understanding of construction sequencing.
Engineering Innovations
Top-down construction and high-stress rock excavation of the Metro Box
The Metro Box was longitudinally divided into a series of 15-metre bays, each initially supported on temporary vertical plunge columns positioned clear of the tunnel boring machines’ trajectory. In each bay, pairs of inclined raking columns were then installed, strutting back into the excavated rock face above the new tunnels.
As construction progressed, loads were transferred from the plunge columns to the permanent raking columns through a technically complex hydraulic jacking system. Once jacked, the temporary supports were removed and the lower plant room levels were subsequently hung from the structure above, enabling the new metro platforms to remain completely column-free in alignment with the architectural intent.
A section through the Main Metro Box showing the staging of the top-down construction
This top-down methodology allowed the upper levels of the station to be constructed first while major tunnelling operations occurred simultaneously beneath, resolving access constraints and enabling significant program efficiencies. The integration of plunge columns, raking columns and staged hydraulic jacking formed the core of the construction-led design that underpinned the successful tender submission.
Central Station Metro: (left) reference design, and (right) winning tender design, typical sections.
Top-down construction is well established, but applying it within stress-sensitive rock strata introduces unique challenges. As deep excavation releases locked-in stresses, movement along the sandstone faces can threaten the stability of partially completed structures above. To manage this behaviour, the team engineered controlled clearances between the slabs and the rock face to decouple the structure from ground movement. Real-time hydraulic jacks were installed at critical interfaces, maintaining constant contact with the rock and automatically adjusting as excavation progressed.
Continuous monitoring of loads, strains and deflections provided engineers with immediate insight into stress-relief patterns, enabling dynamic adjustment of the jacks and ensuring lateral stability while excavation advanced beneath live rail operations.
Central Station Metro: sectional diagrammatic representations of rock stress relief.
This innovative approach delivered:
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Approximately nine months saved on the construction program
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A 38% reduction in concrete volumes and embodied carbon compared with the reference design
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A fully column-free metro platform environment, realising the architectural and operational vision
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Stable, safe construction beneath live suburban, intercity and freight rail operations
This represented a unique application of top-down construction within high-stress rock strata and set a new benchmark for underground station delivery in constrained urban environments.
Central Station Metro: View of the main raking columns prior to jacking
Base of column showing the jacking arrangement. Strain gauges attached to monitor stress during jacking and Engineers monitoring stress and deflection readings during jacking
Photo after successful load transfer, plunge columns were removed
Section through box metro box showing jack location hydraulic and photo of top view of jack