Inland Rail Project – tunnels design, Queensland, Australia

Tunnels will provide entry to Australia’s national freight network and shift more goods from road onto rail

At present, there is no continuous inland rail link between Melbourne and Brisbane, to connect the east coast of Australia. Extensive transit times are endured, and the existing network cannot accommodate long double stacked trains.

The Inland Rail project will mean freight can be delivered faster and more reliably to the country’s population, as well as to global markets.

Connecting Melbourne and Brisbane via regional Victoria, New South Wales and Queensland, the 1700-kilometre freight network will better link producers to markets and create new opportunities for businesses, industries and regional communities.

Aurecon is playing a significant role in the overall programme, having been contracted for a number of projects, three of which include through mountainous terrain in Queensland.

Tunnelling through mountainous terrain

Inland Rail is separated into 13 individual projects, with three of them including new sections of track between Toowoomba and Brisbane. The mountainous terrain at each of the three locations requires tunnels ranging from 1 kilometre to 6.2 kilometres in length.

Aurecon is responsible for the engineering feasibility designs and environmental investigations for the three projects, including the design of the tunnels and tunnel systems in the complex geological environment.

The most significant challenge for the tunnel design and associated ventilation systems is the long and steep grade through the Toowoomba Range. On the climbing grade in the tunnel, the freight trains produce significant amounts of heat and pollutants.

Aurecon’s technical expertise, together with digital engineering tools, produced innovative and safe solutions to meet the unique design requirements.

Purging heat and pollutants

The longest tunnel beneath Toowoomba is just over 6 kilometres in length and represents the single largest item governing the cost, track utilisation and feasibility of Inland Rail. A bespoke tunnel design solution was fundamental for securing the project’s feasibility during development of the reference design and Environmental Impact Statement.

The innovative solution for cooling the diesel freight trains within the confined spaces was the inclusion of a retractable door at each end of the tunnel.

Diesel freight trains require large volumes of air passing over them to remain cool. Retractable doors provide this airflow instead of the traditional method of mechanical ventilation, such as large fans. The closed door ahead of the train forces airflow back over it to aspirate the locomotives. The technique also has sustainability benefits by eliminating the need for any mechanical ventilation as the train travels through the tunnel.

Another feature of the design is an intermediate ventilation shaft to purge the tunnel while the train is still travelling through. This was required to meet the desired headway between trains and satisfy operational capacity requirements. After each train movement, the tunnel must be purged of heat and pollutants to allow passage of the next train.

The intermediate shaft includes a third tunnel door which effectively splits the tunnel into two sections, enabling the sections to be purged at different times. The previously occupied section can then be purged, ready for the next arriving train.

The complex nature of the tunnel and associated infrastructure and systems meant that there were numerous safety challenges to address. These included the steep grade of the rail alignment, and the tunnel control systems that were required to enable a train to safely pass through the tunnel, including interaction with the tunnel doors.

Safety in design workshops were used extensively to identify risks and mitigate them at the design stage.

Tunnel ventilation digital modelling

Designing tunnels for diesel freight trains is rare, and there isn’t any off-the-shelf modelling software available to model the tunnel ventilation system.

Aurecon wrote bespoke code in a digital modelling tool to tell the story of how the heat outputs and pollutants are purged as trains travel through the tunnels. The very complex set of tunnel design outputs was presented in a simple and easy to understand visualisation.

It showed the tunnel alignment, including train movements and door operations. It also presented a transient analysis over time, providing the client with a deep understanding of the tunnel ventilation design; for example, temperature and pollutant levels against the project’s design criteria.

The digital visualisation was critical in facilitating the rapid analysis of numerous train simulations. The client used the design visualisation to interpret and validate operational scenarios.

Aurecon provided an exceptional client experience, demonstrating their deep understanding of the technical challenges associated with the Toowoomba Tunnels and the importance to the Inland Rail Project. The design development process has greatly assisted ARTC to realise and understand our own operational risks and complexities.

– Max Nichols, G2H Project Manager, Australian Rail Track Corporation (ARTC)

At a glance, the three tunnels involve:

  • Single bi-directional dual gauge track for freight operations
  • Accommodation of double-stack container freight trains up to 1.8-kilometres in length, and future proofed for up to 3.6-kilometres
  • Accommodation of the Westlander passenger service for two out of the three tunnels
  • Rail track and tunnel drainage
  • Facilities for tunnel ventilation and smoke control
  • Mechanical and electrical systems, including power supplies, fire protection facilities, communication and security systems, and emergency egress
  • Tunnel control centre

Resilient design for the future

Australia’s freight demand has been forecast to grow by approximately 75 per cent by 2031. ARTC estimates that Inland Rail will reduce truck volumes in more than 20 regional towns and congestion will ease on some of Australia’s busiest highways. Moving freight by rail is four times more fuel efficient than moving freight by road.

Aurecon was able to demonstrate the feasibility of the three tunnels between Toowoomba and Brisbane, in addition to providing an efficient, sustainable and elegant solution. Digital tools played an important role in optimising, visualising and communicating the tunnel design to ARTC and stakeholders.

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