Shoring and dewatering support GPT installation at Spirit of Tasmania Quay

Installation of Gross Pollution Traps (GPT) keeps the new terminal dry and Corio Bay clean

The project

Having outgrown its original terminal at Port Melbourne, in October 2022 Spirit of Tasmania relocated its Victorian operations to a new purpose-built terminal and freight facility in North Geelong. The new 12-hectare site has been redeveloped to include:

• A new passenger terminal

• Marshalling area for up to 600 passenger vehicles

• Upgraded facilities for berthing, boarding and mooring

• Dedicated parking for visitors, passengers, freight clients and staff

BMD Constructions was responsible for landside civil construction, as one of three principal contractors appointed to deliver the new terminal. Coates was chosen to support BMD in the excavation and installation of Gross Pollutant Traps (GPT), designed to prevent stormwater pollution from entering local waterways.

The challenge

When rain falls on large hardstand areas, the water has to go somewhere, explains Coates Product Specialist John Palavras. “A network of drains collects surface water at the terminal and redirects it back into the local waterways,” he says. “But before water can be discharged, it has to go through a filtration system to remove cigarette buts, litter and other materials that don’t belong in there.”

To maintain the quality of discharged water, the new terminal features five collection pits, each fitted with a GPT to filter water as it passes through. One tank holds two GPTs, and the project team faced two main challenges installing these tanks.

1. Waterside location

When excavation work is performed close to water or below the water level, there is a heightened risk of flooding and collapse. To mitigate this risk and accommodate the site’s close proximity to Corio Bay, a robust shoring solution and dewatering strategy was required.

2. Dewatering

The base for the largest excavation was approximately 2.5m below ground level, which made managing groundwater quite challenging. “To prevent the GPT tanks from floating away they needed to be secured to concrete bases, but if the bases didn’t have enough time or a dry enough environment in which to cure, the tanks wouldn’t sit securely in the pit,” John explains. “The pressure was on Coates to keep the pits dry throughout this process, giving the slabs the time they needed to harden up.”

The solution

“BMD originally planned to use sheet piling for most of the excavations,” says Laurence. “But when we realised how long this approach was going to take and factored in the unknown ground conditions, we came up with an alternate sheet and brace solution with Coates that ended up saving us time and money.”

Coates worked closely with BMD to design, certify and implement custom shoring solutions for the GPT pit excavations across the terminal. A combination of proprietary shoring solutions, including slide rail shoring and sheet piling, were used to meet the individual requirements of each site.

Slide rail shoring

According to John, slide rail shoring was used extensively to support the GPT pit excavations. “Slide railing isn’t watertight, but the further we got from the water’s edge the more we used this technique. And when we did encounter water, we were able to quickly install localised pumps to keep the excavation sites safe and dry,” he says. “This proprietary, engineered slide rail system won’t suit every application, but it worked well for this client, and on this particular site.”

Sheet piling

To support the installation of the GPTs closer to the water, a robust sheet piling solution was deployed, internally braced by a Coates proprietary Mega Brace system. GPT 4 was the largest excavation supported in this way, measuring 17m (L) by 5m (W) and 5.45m (D).

“Because the ground conditions were so challenging for this excavation, we designed a system that incorporated walers positioned at 4 different levels, braced with Mega Brace hydraulic rams,” John explains. “Additional support was provided by SYS 100 struts, and well-point dewatering was used to manage water within the excavations.”

The impact

This project builds on a longstanding relationship between Coates and BMD, and a history of successfully partnering to deliver infrastructure and civil works projects across Victoria.

“BMD has always had a close relationship with Coates for equipment hire. I hadn’t previously worked with Coates on temporary works projects, but I had heard good things from other colleagues,” says Laurence. “As we needed a reliable solution and quick turnaround, we knew Coates was the best way to go.”

“It turned out to be a really positive experience working with Coates. The guys on the ground were easy and professional to deal with. We had some trouble getting the shoring to connect with what we already had in the ground, but they worked well with us to resolve the issue,” Laurence continues. “Coates was also quick with turnarounds for pricing and sourcing equipment which kept us on schedule. We also found it much easier dealing with one company for both the shoring and dewatering solutions.”

Need to shore and dewater an excavation? Contact the Coates Engineering Solutions team today