USA’s contract was to excavate; install the foundations, and erect the new poles. The excavation was done using an Auger, mounted on a 20 t excavator. The ground conditions were predominately clay with some rock and the water table at about 3M. The foundations varied in size in diameter and depth depending on the type of pole. The largest was 2.5M in dia and 8.5M deep. The formwork was a 10mm steel plate rolled and welded to form a 2.5M x 1.8M high section. These sections were installed and welded. One of the more challenging stages of construction was the installation of the 5mm Poly Ethylene membrane used as an insulator. A first for Western Power in an attempt to safe guard other utilities infrastructure from lightning strikes.
One other challenge was the erection of the new poles adjacent to the PTA’s rail system on Sevenoaks Street Cannington. The next stage involved the positioning of the reinforcing cage into the formwork. These cages had to be orientated specifically to suit the pole type, and so that the cross arms would be facing the correct way. The concrete for the poles was poured using a boom pump and vibrated constantly until the pour finished. There was a curing period of 14 days before any poles could be erected. The pole cross arms and insulators were fitted on-site before the poles were erected. Two cranes were used to lift the poles into position, a 50t for the main lift and a 20t Franna to support the base. This took between 2 and 3 1/2 hours depending on pole size. The four poles adjacent to the railway line along Sevenoaks where erected between 1.00am and 4.00am this was at the request of the Public Transport Authority to ensure there was no chance of injury to train users. Once in position Western Power Line crews transferred the conductors from the old poles to the new ones. The project was completed on time and with little or no adverse impact on business or residents in the area.
