Client name: Roads and Maritime Services (RMS)

Duration: September 2007- December 2012

Location: Ballina, New South Wales, Australia


Working as part of the Alliance, Coffey initiated a number of innovative practices that contributed to an early completion date – six months ahead of schedule.  

Situation

The Pacific Highway Ballina Bypass crosses the Richmond River floodplain – some of Australia’s deepest (up to 28m) and softest soils – which are subject to large and varying rates of settlement. These difficult ground conditions require extensive measures to prevent embankment failure and ensure cut stability. Soils are also acidic, containing naturally occurring heavy metals that pose contamination risks.

This $600m road runs between Ballina and the Bruxner Highway. It includes 11.5km four-lane dual carriageway and 12km of local roads, 3 major interchanges and 19 bridges – including over water structures.

Solution

Low embankment strategy – We developed a low embankment strategy to reduce the extent of ground treatment required for lengthy sections. This kept the embankment as low as possible, while maintaining flood immunity for at least one traffic lane in a 1:20 year flood event.

To allow for post-construction settlement, we designed a staged flexible pavement approach, using moisture-resistant pavement and reshaping after one year of operation. The fill was placed as early as possible. A flood gap strategy ensured parts of the embankment could be removed quickly to allow flood water to pass.

Cutting stabilisation By understanding the geology of the rock cuttings through investigation and geological mapping we were able to significantly reduce the rock support requirements for the major cuttings on the project.

Innovative ground treatment techniques – Following detailed site investigations, we installed extensive ground treatments to control embankment settlements and overcome the difficult soft ground conditions. These included: lightweight fill, surcharging with wick drains, vacuum consolidation (an Australian first), dry deep soil mixing, vibro-replacement stone columns and dynamic replacement.

These ground treatments were also selected to minimise disturbance of the natural soils. In addition, groundwater was extracted and treated to neutralise acid and heavy metals.

Result

Major cost savings – The low embankment strategy alone saved the project over AU $20m.
Delivered early – This component of the Pacific Highway opened six months earlier than its anticipated completion date. Average road performance is expected to meet or be better than project specifications.
Success despite soft soil conditions – RMS considered Coffey’s work on the soft soils pivotal in overcoming the difficult terrain. Our solutions enabled roads to be constructed in areas where it was not previously thought possible.

 

“Just a brief note to say thanks to the team for a fantastic job, well done. Whilst there are still a couple of important milestones to hit, the major objective of the project has been achieved. Achieved with bells and whistles – achieved early, achieved with a focus on working safely, achieved with an attention to detail and quality, achieved with the interests of the community and travelling public in mind. The project has faced some incredible engineering and construction challenges and I don't think could have achieved this result without the collaboration of the project partners possible through the alliance.”

Geoff Fogarty, Director Infrastructure Services
Roads and Maritime Services (formerly RTA)
November 2011