Western Australia Chapter

Geotechnical and Pavement Engineering Aspects of the New Perth Bunbury Highway

Russell A Clayton

The New Perth to Bunbury Highway located south of Perth is the largest road project that Main Roads Western Australia has ever undertaken. The project, delivered through an Alliance, comprises 70 km of dual carriageway freeway and highway with 23 bridges, of which 4 were incrementally launched across the larger rivers.

The geotechnical ground conditions vary significantly along the length of the site and in profile. Significant portions of the area are low lying and are subject to seasonal inundation for extended periods, which created challenges with the highly expansive soils and the risk of inundation of the pavement structures due to capillary rise.

Nearly half of the 11 bridge sites have complex soil profiles that varied significantly from pier site to abutment, due to the presence of palaeo-channels that created challenges for the foundation design. Pre-treatment of the foundations to the embankments included wick drains and preloading. Embankments that had to be constructed on weak foundations were both pre-treated with wick drains and carefully preloaded under controlled conditions to prevent overstressing and failure. Geotechnical instruments were extensively used on the project and provided some interesting insights into the ground behaviour at some of the sites and significantly accelerated the rate of construction due to a better understanding of the soil responses.

The foundation systems were tailored to suit the ground conditions and included shallow and piled foundations (including tubular steel, precast concrete and Franki piles). The highly corrosive environment required the careful consideration of corrosion protection. Innovative grouting techniques were applied in some areas to ensure positive contact between the pile end and the in situ material.

Three different pavement designs were adopted for various sections of the alignment and were selected based on a detailed whole of life assessment. A trial pavement that was exposed to accelerated loading provided good insight and confidence in the performance of two of the chosen designs.

The procurement and control of the vast quantities of materials used to construct the road formation presented their own challenges and will be discussed. Research into the typical WA materials used on the project provided illuminating insight into their likely long term performance. The presentation aims to be informative and should appeal to those who have a general interest in geotechnical and civil engineering in a road construction environment.

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