An ambitious project at the Port of Melbourne presented a number of engineering challenges, but the toughest one was hidden beneath the surface.
More than a century of industrialisation had left a layer cake of waste between the Port Rail Transformation Project (PRTP) site’s ground level and its Coode Island silt base. Along with pockets of PFAS chemicals and fill material, there were old concrete slabs, asphalt pavers and random bands of scoria in the mix.
A key aim for construction is to recycle as much of the site’s existing materials as possible.
Latent ground conditions have tested this goal, but engineers are confident that the land will be left in better condition than before the project broke ground in December last year.
Site investigations for the Port Rail Transformation Project began in March 2021, a month after the engagement of engineering firm WSP and Seymour Whyte Constructions.
Despite the series of COVID-19 lockdowns across Melbourne, the design phase remained on track, thanks in part to WSP’s cloud-based platform, which enabled remote collaboration between the project partners and their Port of Melbourne client.
Spanning more than 500 ha of land at the mouth of the Yarra River, the Port of Melbourne handles about a third of Australia’s container trade.
The PRTP is part of a broader state and Commonwealth Government strategy to improve rail freight across Victoria. Almost 95 per cent of the state’s import containers are destined for metropolitan Melbourne, and the vast majority of freight is currently moved by road.
The project incorporates the development of new rail infrastructure at the port. A new rail depot will interface with the container terminal at Swanson Dock East International Container Terminal and includes two new rail sidings that can each handle 600-metre-long trains.
While a B-double truck has capacity to transport an average of up to four 20-foot containers, a train of this length can carry up to 84 of them.
A road will also be built to support the uninterrupted movement of containers. It will provide a continued east-west connection within the Swanson Dock Precinct without trucks needing to exit onto busy Footscray Road.
“A key aim of the project is to facilitate and increase rail-road share,” said Matthew Brooks, Senior Project Manager, Port Rail Infrastructure at Port of Melbourne.
“It’s about taking more trucks off inner-city roads and putting more containers on to trains destined for outer-suburban logistics terminals.”
Beneath the surface
Latent ground conditions presented the bulk of the project’s engineering challenges. Brooks said extensive geotechnical and environmental investigations were required to determine exactly what materials they were dealing with and what could be reused.
“Being in a port environment, especially being on Coode Island where lots of different fill materials have built up over time, we knew that we had to deal with changing ground conditions and have a design that could last the 50-year design life,” he said.
“But working out what we could reuse was tough. I think we went above and beyond in our investigations to determine this.”
Brooks estimates that approximately half of the construction site had layers of pavement beneath the surface.
“When you dig down, you can find five or six different pavement layers dating back 40 or 50 years, and it’s all just been built up on top of each other,” he said. “Throughout our investigations, we needed to understand what of the existing materials could be crushed up or removed and then stockpiled and put back in as crushed rock materials or in the sub-base pavement layers. We didn’t want to take those materials offsite or remove contaminated materials and put them into other landfills.”
Recycle and reuse
The PRTP is adjacent to the troubled West Gate Tunnel Project, which faces significant cost blowouts and delays due to the handling of about three million tonnes of soil contaminated with PFAS — per and polyfluoroalkyl substances — a group of potentially toxic manufactured chemicals used in everyday products from waterproof jackets to stain-resistant cookware.
Maurice Gubiani, Environmental Manager at Seymour Whyte, notes that PFAS and Category D waste were also identified during early phase investigations of the PRTP site.
“We got a full contamination map of the site, so we knew exactly where the PFAS was, for example, and we put that into our design and marked it out on site,” he said. “We anticipated that we’d be able to use reuse a certain quantity of material that we’ve been given permission for from the [Environment Protection Authority (EPA)].”
“We had a pretty good grasp of what was going on under the surface,” adds Gubiani. “But the heterogeneity of the waste made it so tricky, because we’d work on one section and it was exactly as we’d anticipated and it fell into our reuse-of-material plan, but then we’d move five metres, and it was something totally different.”
Rail terminals require heavy duty pavements to support the weight of containers.
A 40-foot container can weigh about 35 t when fully loaded and Brooks was working with the WSP team to design pavements that could withstand the weight of four containers stacked on top of each other.
The PRTP recycling challenge will be overcome through site investigation and lateral thinking, but technology helped to address challenges during the design phase, despite interruptions from COVID-19. The final design was completed within 12 weeks, including a preliminary design submission at the six-week mark.
Robert Freeman, Digital Operations Lead for WSP Transport, said the company’s cloud-based digital platform, WSP Create, allowed stakeholders to access, visualise and share key information. The platform integrates the ProjectWise 365 and iTwin Services tools from Bentley Systems.
“There were times during COVID where we couldn’t get to the site, but WSP Create allowed everyone to log into the project and, depending on the stage of the project, they could go straight into a 3D model, review the design and request any changes,” he said.
Improving the land
Practical completion of the PRTP is slated for early 2023. Along with providing new port infrastructure and removing more trucks from Melbourne’s inner-city roads, Brooks believes the project will result in better land conditions.
He said they want to leave the land in a better way than when the project started.
“I think we can comfortably say that we’ve explored all avenues possible for recycling and reducing our disposal rate,” he said.
“This is not just because it makes sense for us, but because it’s the right thing for engineers to do”.