A complex civil engineering project in the heart of Sydney required a flexible and efficient shoring solution in the excavations.
In order to reduce flooding in Sydney’s inner-city Green Square development, and to facilitate the building of the Green Square Town Centre, an alliance is constructing a 2.4 km stormwater drain that connects Zetland to the Alexandria Canal.
The system is being constructed by the DG Alliance Sydney: Sydney Water Corporation, City of Sydney, UGL Engineering, Seymour White, Parsons Brinckerhoff Australia and RPS Manidis Roberts. And specialist infrastructure company Brefni installed the deep pipe and caisson sections of the works.

The stormwater system is located underground but constructing it required deep trenches to build the twin-stormwater pipes, and large caissons containing gross pollution traps (GPTs). To complete the project on time, and to ensure worker safety, the trenches and pits had to be effectively shored.

Scott Fraser, General Manager of Construction for Brefni, says the project was complex: excavations were at some points eight metres deep, and one was 12 metres across; the main trench included a 90-degree corner as well as curves and slopes; and there were problems with ground water and contaminated soil.

“We initially used traditional sheet-pile walls to shore the trench walls, but it was taking too long. So we turned to Coates Hire,” says Fraser. “They have a propping system that uses hydraulic rams which can be adapted to the size of the excavations very quickly and effectively.”

Fraser says the caisson around the GPT required a pit 12 metres wide. The work area could not be impeded by the I-beams traditionally used in sheet-piling across a wide area.

The Coates Hire team didn’t just have the hardware and the service – they had an entire solution.
Scott Fraser General Manager of Construction for Brefni

“Coates Hire’s shoring system meant large amounts of cross-bracing didn’t have to be used, and allowed the work to be done more effectively.” Fraser says Coates Hire provided engineering support to design and deliver the solution. “The Coates Hire team didn’t just have the hardware and the service – they had an entire solution.”

Darren Browne, Temporary Works Engineer at the Coates Hire Engineering and Technical Services Team, says the contract was conducted in five separate stages, over 200 metres of trench-runs and pits. The client also made a decision to engage Coates Hire on the basis of safety, because using a crane to lift steel sheets and beams with nothing but chain-chokes, could have become a hazard.

“Our Mega Brace system has certified lift points, and it’s modular. There’s no need for welding and gas-axing in the pits and there’s no slippage of steel on chains. For these complex excavation jobs, with no room to move, the Mega Brace system comes into its own.”


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