Client name: Roads and Maritime Services (RMS)

Duration: November 2009 – June 2013

Location: Kempsey, New South Wales, Australia

Specialised solutions were required to address the significant challenges brought about by construction on soft soils on the Pacific Highway. 

Building Australia’s longest bridge on deep soft soils containing acid rock

The $370 million Pacific Highway Kempsey Bypass project runs between Kempsey and Frederickton and consists of a 14.5km dual carriageway, two interchanges, three overpasses and one bridge spanning 3.2km – the longest in Australia.

Construction was on a floodplain with soft soils up to 25m deep. This made it difficult to design embankments and structures, since foundations have a tendency to settle many metres after road and bridge construction.

Another major challenge was to reuse as many materials as possible, without compromising structural integrity.

As the project was located within areas containing acid rock, which is considered a major environmental issue, appropriate testing and a treatment regime was also required. Potential contamination on land being acquired for construction of the Frederickton levee also needed assessment, and then management during construction.

Innovative controlled modulus columns for the load transfer platform

We designed controlled modulus columns to support the approach embankments on soft ground leading to the 3.2km flood plain bridge. This involved an innovative solution that removed the need for traditional high strength structural geofabric in the load transfer platform.

Working closely with the project team, we led the technical study and field trials, including identifying onsite materials that could achieve structural performance requirements and meet Roads and Maritime Services specifications, with minimal processing.

To minimise disturbance of natural soils and waste generation, we provided specialist advice on the potential environmental and engineering effects of acid rock drainage during road construction. We also undertook due diligence contamination studies at the site of the Frederickton levee, prepared a contamination management plan and provided guidance on management of contamination and waste during construction.

Using our on-site materials testing laboratory to ensure materials consistency and structural requirement, we developed field processes to ensure geological changes were identified at the cuts every day – and taken into account.

Award-wining project delivered early and under-budget 

The Pacific Highway Kempsey Bypass project was completed under budget and opened 14 months ahead of schedule.

The Alliance was awarded the Roads and Maritime Services 2012 ‘Highly Commended Award’ under the category of ‘Quality Innovation’ for the work completed on materials management, as well as the Sustainability Leadership Award from the United Nations Association of Australia.