The pumping station site sat at 9 metres below ground level, in poor soils. When excavations started Sydney Water hit the water table at around 3 metres in depth, meaning increased risk of subsidence in the pit walls and inundation at the base of the excavation.
Sydney Water contracted Coates Hire Engineering and Technical Services, to design, build, test and install a shoring system that would hold the sheet pile walls of the pit, while also dewatering the excavation site so the works could be carried out.
Temporary Works Engineer at Coates Hire Engineering and Technical Services Team, Darren Browne, says the pumping station at Wolli Creek was a complicated site which needed to be secured before workers could safely operate.
“There was nothing simple about the site due to the confined site boundaries, a number of existing services both overhead and below ground, the deep excavation depth and extremely challenging soil and groundwater conditions,” says Browne.
He says Sydney Water had to re-scope the project as they gained more information, but Coates Hire’s Mega Brace shoring system was adaptable to changing conditions. The pit walls were held-up by four Mega Brace hydraulic braces, installed incrementally as the excavation proceeded, creating a wall that was supported during the work.