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.