How changing a tunnel method can strengthen sustainability outcomes

The Western Harbour Tunnel is a major infrastructure project designed to ease congestion and improve journey times across Sydney by creating a new crossing beneath Sydney Harbour.

Originally proposed as an immersed tube tunnel (IMT) involving seabed dredging and placement of pre-fabricated tunnel segments in a trench on the harbour floor, the project underwent a significant revision to reduce environmental and community impacts. 

Group photo of workers and project team members in front of the tunnel boring machine for the Western Habour Tunnel. The tunnel boring machine cutterhead is decorated with Aboriginal artwork. Team members wearing high-visibility clothing and safety gear pose inside a large CREG industrial facility during the factory acceptance testing in China.
Close up of the tunnel boring machine named Patyegarang of the Western Harbour Tunnel project. The tunnel boring machine features Aboriginal artwork on its cutterhead and a large name panel displaying project partners, including Acciona and CREG, The machine is positioned inside a large CREG facility in China.
Cross-section diagram of a tunnel boring machine showing labelled components, including the cutting wheel, bulkhead, air cushion, tunneling shield, air lock, thrust cylinders, slurry circuit and permanent tunnel lining.
Map of Western Harbour Tunnel showing Stage 1 (blue) and Stage 2 tunneling (red for tunnel boring machine (TBM), green for roadheader). Key locations like Rozelle, Birchgrove and North Sydney are labelled. Several construction support sites are marked as no longer required. TBM launch and receival chambers are shown at Birchgrove and Waverton.

During design development and construction planning, the project team identified opportunities to improve sustainability outcomes by shifting to a Tunnel Boring Machine (TBM) solution. While IMT was considered acceptable during initial planning, further analysis and stakeholder feedback highlighted risks to biodiversity, water quality, and local amenity, especially in ecologically and culturally significant areas such as Berrys Bay and Yurulbin Point.

The updated approach aimed to protect the marine environment, reduce impacts on harbour-side communities, enhance safety and constructability, and demonstrate Transport for NSW’s commitment to sustainability and adaptive project delivery. 

Approach and implementation

As part of the Environmental Impact Statement (EIS) process, over 15 combinations of tunnelling methods, including a TBM solution, were considered. The IMT method was originally selected as the preferred option based on its performance across criteria such as constructability, traffic outcomes, and environmental impact.

However, during detailed design development and industry engagement, several key developments supported a shift in methodology.

Supporting factors for methodology shift
  • technological advancements in TBM capabilities, including experience from the Sydney Metro City project
  • increased understanding of local geology and construction feasibility for tunnelling under the harbour
  • community and stakeholder feedback expressing strong concern over the impacts of IMT construction.

 

During the tender process, contractors were invited to propose alternative delivery approaches. Acciona submitted a bid featuring a TBM solution that would eliminate the need for dredging and remove several high-impact construction support sites. This included replacing marine-based works with deep tunnelling beneath the seabed and developing a new precast segment facility at Emu Plains.

Cultural storytelling in tunnel delivery

At Transport, we are committed to embedding Aboriginal perspectives in infrastructure planning and delivery. As part of this commitment, the Western Harbour Tunnel project includes cultural elements that reflect local Aboriginal identity through:

TBM naming

Two tunnel boring machines have been named Patyegarang and Barangaroo, honouring influential Aboriginal women:

  • Patyegarang was among the first to teach an Aboriginal language to a non-Aboriginal person, marking an important moment of early cultural exchange
  • Barangaroo was a respected Cammeraygal woman and fisherwoman who paddled Sydney Harbour in traditional nawi (canoes), symbolically crossing the same path the tunnel will follow.

TMB artworks 

  • The cutterheads of both machines are decorated with vibrant Aboriginal artworks, reflecting the stories of Patyegarang and Barangaroo.

Tunnel and PPE design

  • Aboriginal designs will also be featured inside the tunnel and on the PPE worn by workers, supporting cultural visibility throughout the project. 

Outcomes and impact

In 2022, a formal modification to the planning approval was submitted to adopt the TBM approach. This resulted in several key impacts.

Key impacts of TBM approach adoption
  • removal of dredging activities and the IMT fabrication site at White Bay
  • decommissioning of five approved construction support sites, including Berrys Bay, Yurulbin Point, Victoria Road, and Sydney Harbour cofferdams
  • relocation of surface works at Rozelle to an underground support site, enabling earlier delivery of Rozelle Parklands.

 

This alternative approach reflected a risk-informed, stakeholder-responsive model of infrastructure delivery, with strong alignment to Transport’s sustainability and community priorities. This project achieved a variety of environmental, social and economic benefits through its implementation.

Environmental benefits
  • eliminated the need for dredging in Sydney Harbour, significantly reducing ecological disturbance
  • preserved 10.51 hectares of deepwater soft sediment habitat, 0.01 hectares of Black Rockcod and White’s Seahorse habitat, and 0.03 hectares of seagrass
  • improved water quality outcomes by avoiding sediment resuspension
  • reduced spoil generation by approximately 32 per cent due to both the removal of dredging and the reduction in surface construction sites
  • decreased water demand by removing the need for five support sites
  • avoided construction in culturally significant foreshore areas, contributing to heritage protection. 
Community and social benefits
  • reduced noise, traffic, and visual impacts in sensitive locations such as Birchgrove and Waverton
  • preserved and accelerated community access to public open spaces and foreshore parks
  • built trust through transparent, adaptive decision-making and clear communication
  • enabled earlier delivery of the Berrys Bay Foreshore Parklands for community benefit.
Economic and delivery benefits
  • improved safety and navigational access for harbour users, including ferries and recreational vessels
  • minimised disruption to local businesses, such as Sydney Harbour Yacht Charter in Berrys Bay
  • consolidated construction zones for more efficient logistics and streamlined delivery
  • demonstrated innovation in infrastructure delivery, supporting local construction industry confidence in complex tunnelling projects.

Lessons learned and future considerations

The project implementation generated valuable insights across multiple areas.

What worked well
  • early and frequent engagement with stakeholders helped shape better project outcomes
  • a whole-of-life view of sustainability - including long-term environmental, social, and cost benefits - informed smarter delivery decisions
  • TBM delivery proved to be a successful method for complex harbour tunnelling with measurable gains across all sustainability domains.
Challenges and how they were managed
  • changing the construction methodology required additional design and approval processes, including new tunnelling support infrastructure at Emu Plains
  • harbour tunnelling introduced new geotechnical and safety challenges, addressed through robust risk management and inter-agency coordination
  • program impacts were managed through collaborative planning across government and delivery partners.
Advice for future projects
  • consider the full environmental and social costs of marine construction methods early in project planning - and reassess throughout the design lifecycle
  • build flexibility into planning approvals to accommodate emerging technologies and better delivery approaches
  • use stakeholder feedback as a genuine opportunity to improve outcomes, not just a consultation requirement.

 

Why this matters:

The decision to switch from IMT to TBM construction for the Western Harbour Tunnel represents a landmark shift in how major transport infrastructure can be delivered more sustainably. It demonstrates how responsiveness to community input, advances in technology, and a focus on long-term environmental protection can lead to better outcomes for people, place, and the planet - setting a new standard for future coastal and harbour-based tunnelling projects.

Related links

For more information on the project, please visit: