3 Centuries of Progress
Motorists heading towards Melbourne on the Prince’s Freeway from Geelong may be fleetingly aware of some construction activity adjacent to the bridge over the Werribee River. What they are zooming past is an engineer’s snapshot of Melbourne’s growth and construction techniques across three centuries.
A partnership between Melbourne Water, Fulton Hogan, Jaydo Construction and GHD; the Pipelines Alliance is currently constructing a new Werribee River aqueduct as a critical component in a five-year program of major works to prepare Melbourne’s sewerage and draining systems to meet the demands of the 21st century. The new aqueduct runs parallel to a smaller concrete structure built in the mid 20th century, and a heritage listed, open, red brick aqueduct that was constructed in the 1890’s. On completion, the new aqueduct will deliver up to 60% of Melbourne’s sewage to the nearby Western Treatment Plant.
The new structure has a 5.4m square cross section and spans 70 metres over the Werribee River, creatively designed and constructed utilising a mix of concrete construction methodologies.
The aqueduct is supported by piers resting on piled foundations up to 8 metres deep. The piers and headstocks are made up of large precast concrete elements, each of which weigh between 22 and 29 tonnes.
The main aqueduct spans were constructed from 4 concrete box girder sections, each of which are 17.5 metres long and placed via an incremental launch process. Each box girder section was, in turn, cast on site in two parts that were joined before the completed girder section was set in place in the launching “train”.
Flows to and from the main aqueduct spans will arrive and depart via a 4.7m diameter pipe, constructed from precast concrete arch sections lined with High Density Poly Etheylene (as are the aqueduct box sections). Each of these sections weighs up to 35 tonnes, and had to be designed to withstand the variety of loads imposed during de-moulding, rotation, transport and placement.
Precast walkway units attached to the top of the aqueduct and pipe and transition units will enable the finished structure to serve as a footbridge and a key link in the Federation Trail bike path.
Reid was able to make a contribution at each stage of the project. The Reid engineering team worked closely with GHD during the design phase, conducting lifting analysis for the headstock, pier and walkway units. Reid also provided lifting analysis for Fulton Hogan of the very intricate two crane rotation required with the arched pipe segments.
Temporary retaining walls protecting the piling works, the pier construction, and the abutments to the main section launching bay were secured with ReidBar™ continuously threaded reinforcing bars and couplers. Stainless steel Reid Elephant Foot ferrules are used in the expansion joints that provide an essential degree of structural flexibility.
Reid lifting anchors were used to position the pier and headstock units, the arched pipe sections and the walkway units. Halfen channel was cast into the lower face of the walkway units to provide support for a suspended water main.
By the end of 2010 a few cyclists and pedestrians crossing the new aqueduct may pause to glance across at the 19th century structure, and wrinkle up their noses at the thought of the raw sewage that used to flow along its open channel; laboriously constructed brick, by red brick. Most of them will not realise they are standing on its 21st century equivalent, made real by the Pipelines Alliance and REID.