GHK Piling won a contract for the pile driving and construction of 16 foundations for flood lighting for the William Fraser Memorial Sports Field on Pohe Island, Whangarei. Each foundation had 4 300 SED piles driven up to 18.0m into the ground and a reinforced concrete pile cap with the light hold down bolts cast into them.
One of the main challenges on the project was that the piling was on top of the old Whangarei dump and there was significant risk of obstructions when piling. There was also risk that pile driving operations would compromise the clay cap which could lead to methane gas being emitted from the ground.
During the construction we used a gas detector during all pile driving operations to ensure that methane gas was not present. At one time, the gas detector did detect gas and works were stopped for 15 minutes, retested and it was clear. We believe the swirling wind caused the detector to pick up the exhaust of the crane.
The piles required significantly more energy to drive than anticipated. A steel probe was effective at clearing minor obstacles and making sure the piles could be driven to a depth that they were well beyond the refuse layer (which was a requirement of the engineer). We were able to utilise specialist pile driving equipment to drive the poles at full length without requiring a splice.
A steel spike (probe) enabled us to identify one location where we could not drive the piles. Historical records showed this location was the old haul road for the dump and was likely to have a pavement up to 1.0m thick. We were able to use the spike to identify the nearest location that we could successfully drive the piles and the required lighting level could be achieved by only changing the angle of the lights.