To service forecast increased population levels
Bundaberg Regional Council embarked on a $90M project to construct a new waste water treatment plant at Rubyanna, located between the towns of Bundaberg and Bargara in central Queensland
As part of this treatment plant, a new discharge was required into the Burnett River.
The river discharge was procured as a design and construct contract, for a scope of works including a 150m long discharge pipeline and an onshore overflow pit.
Brady Marine & Civil developed an optimised design and methodology which required less materials, reduced environmental impacts and was able to be constructed in a shorter time period.
Scope of works included:
- Design of all works including permanent and temporary works.
- Driving of twin Supply & installation of twin 150m long 900mm hdpe pipelines by the “float and sink” methodology.
- Driving of 22 nos tubular steel anchor piles
- Fitting by divers of hdpe diffuser pipelines with pre-fitted duck-billed diffuser ports
Special Features
A single 1200mm diameter pipeline which had been indicated in the original concept design was replaced by two 900mm pipelines. These were set parallel, each ending with half the required number of diffuser ports. As well as reducing by one third the required number of offshore supporting piles, this arrangement enabled the completed facility to better deal with a staged capacity as the WWTP inflows grew steadily in the future.
Through optimising the alignment, chainage and support of the discharge pipelines, all offshore dredging was eliminated in Brady Marine’s solution. This meant that no dredged spoil needed to be disposed of and also meant than no scour rock was required to be supplied or placed offshore as the existing seabed was not disturbed.
With a smaller pipeline diameter, our solution utilised trenchless technology to enable the pipelines to be installed to an exit point in the river without impacting on the existing shoreline. In so doing this avoided the need for shoring and construction access through the riverbank, eliminated any damage to the natural shoreline and associated flora and saved any requirement for scour protection after laying the pipe.
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Special Features
Substantial reuse of materials and components used in the construction of the works was achieved. The sheet-pile waling system, for example was purchased second hand from the Perth Metro rail project and subsequently sold to the Alkimos project north of Perth on project completion.
Constructing the works progressively in short cofferdams required an innovative solution at the junction between cofferdams. Issues to consider such as retaining backfill behind the pipe starter length from the previous cofferdam and avoiding damage during subsequent excavation required careful thought. The solution adopted fulfilled all of these criteria and successfully completed the joints 14 times along the length of the pipeline.
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