NorthConnex: Adaptive supply of lattice girders

Mainline excavation of Sydney’s NorthConnex tunnel is coming to an end thanks to a steady and adaptive supply of prefabricated lattice girders used to provide structural support to the tunnel.

Sydney’s NorthConnex will be Australia’s deepest road tunnel when complete. Not only will it create a vital link in Sydney’s transport infrastructure, it will allow motorists to travel between Newcastle and Melbourne without encountering a single set of traffic lights.

The project has benefited from InfraBuild Construction Solutions’ (formerly LIBERTY OneSteel Reinforcing) efficient supply chain, which has included the integrated manufacture, processing and delivery of complex and adaptable steel reinforcing lattice girders.

The lattice girders have formed an integral part of the primary passive ground support design, providing a safe work area to continue tunnel excavation. Ground conditions, low ground cover areas and tunnel profile typically govern lattice girder section properties and overall specification. As the profile changes depending on the number of traffic lanes, cross passage intersections and mainline sections in the tunnel, so too must the requirements for the manufacture and installation of lattice girders.

Meeting the tunnel’s requirements

InfraBuild Construction Solutions’ Con Komselis says that meeting the tunnel’s varying requirements has been an important factor in the project’s construction. 

“InfraBuild Construction Solutions tendered for the supply of lattice girders to the NorthConnex Project by the Lendlease Bouygues Joint Venture (LLBJV). We were aware that the lattice girder configurations were likely to be complex in order to meet tunnel support specifications,” he says.

“InfraBuild Construction Solutions has over 20 years’ experience in the manufacture of prefabricated ROMTECH® lattice girders, supplying several major tunnel projects constructed using roadheader development. We were confident in demonstrating our capability and knowledge in the bespoke design and supply required to ensure the key tunnel criteria would be satisfied.”

The complexity of the project meant that significant work was required once the tender process was concluded to complete the prefabrication drawings and finalise the supply program. The prefabrication drawings required all elements to be specified inclusive of welding and bolting requirements. The design was unusual in that end plates were bolted rather than welded, thus allowing for variation in ground conditions and flexibility in adding sections if required.

Adapting supply as needed

During construction, it was important for the supply of lattice girders to be flexible to maximise efficiencies in the construction program. With a production site in both Sydney and Brisbane, InfraBuild Construction Solutions was able to use a ‘two-site solution’ to adapt its prefabrication production to maintain supply to provide this flexibility, including manufacturing multiple profiles simultaneously.

Close collaboration with the site engineer over the course of the project meant that section dimensions could be optimised to accelerate production, reduce lead times and simplify the installation of the lattice girders.

Jeremy Guerin, Senior Project Engineer with LLBJV, said that it’s very important to have flexibility in the supply chain.

“Tunnelling on NorthConnex has been a 24/7 operation and flexibility in the supply chain has been essential for us to maximise efficiencies in tunnelling production,” Jeremy said. “We found InfraBuild to be very responsive to our needs. We had a direct line of communication with Con and his team, were able to tell them what was going to be required next and they would respond rapidly, delivering the required girders on time, meaning we didn’t have to slow the pace or stop excavation.”

Compliance to AS1554.3

InfraBuild Construction Solutions’ extensive training and education of its prefabrication teams meant that it achieved compliance to AS1554.3. Its integrated supply chain, from manufacture to prefabrication and delivery, allowed for full traceability and compliance of materials and prefabrication to Australian standards, with ACRS certification.

From June 2017 through to the completion of the supply contract in August 2018, InfraBuild Construction Solutions supplied a total of 470 complete lattice girder sets and 30 leg extensions in 12 different profiles to the NorthConnex project. Peak supply was 30 lattice girders per week from both of its sites. 

Con believes close collaboration is key to satisfying the requirements of a large-scale and complex project like NorthConnex.

“Successful supply includes understanding the client’s construction requirements, meeting the supply program, building trust and gaining knowledge of their complete scope of works,” he says. 

“Above all, having direct and continuous communication with key site personnel allows for prompt changes to design, supply and delivery.”