27 October 2004
Jacking pipes deliver future of city power supply

Rocla is supplying 1800mm diameter Rocla® Jacking Pipe to Diona Elbac for one of the biggest jacked pipe installations ever undertaken in Sydney.

A total of 400 metres of the large diameter concrete pipe will be used at 8 locations to provide tunnels for underground electricity cables.

The tunnels are part of a new 28km high voltage underground cable from Picnic Point in the south to Haymarket in the city that will boost electricity supply and help meet increasing demand.

The project, called MetroGrid, is part of a $500 million upgrade of the city’s power supply by statutory authority TransGrid, which is responsible for the NSW transmission network linking generators and distributors.

Most of the 28km of cable is being laid in open-cut trenches, with some trenchless jack-piped sections, while the last 4 kilometres into the city will be laid in a specially constructed tunnel.

To minimise disruption, the route is located mainly beneath public roads.

Pipe-jacking is being employed by civil contractor Diona Elbac to tunnel under inaccessible areas, such as railway lines on Sydney’s busy southern rail network.

The first 50 metres of jacked pipe were installed successfully at Kingsgrove and Diona Elbac is currently boring a 45-metre tunnel under rail lines at Marrickville. The pipe tunnels carry five lengths of 200mm PE conduit attached to the sides: three for 330kV electricity cables; one for a fibre-optic cable; and one spare.

The pipe is then filled with grout to protect the conduit. Large diameter pipe is required to allow sufficient space to dissipate heat generated by the cables. Because of existing services buried beneath the rail lines, the pipe tunnel is running at depths of 5 to 7 metres.

Rocla engineers worked closely with the installers to ensure the steel reinforced concrete pipes would meet all load requirements, which include pressures of up to 5000 tonnes exerted by the hydraulic pipe jacking equipment.

The 1800mm diameter pipes are being supplied in standard 2.4-metre lengths, which are butt-jointed with steel bands, also supplied by Rocla.

Jacking pipes deliver future of city power supply