A Comprehensive Geotechnical Investigation For The New Bridge Over The Clarence River At Harwood

The new bridge over the Clarence River at Harwood forms an integral part of the Pacific Highway upgrade in northern NSW and is currently under construction by the Acciona-Ferrovial Harwood Joint Venture (AFHJV). The proposed bridge extends 1.5km between abutments, spans the Clarence River with a water span of approximately 560m and is founded on 2m to 2.4m diameter driven hollow steel tubular piles to over 60m depth in some areas.

The underlying geology of the site consists of 30 to 40m of soft estuarine silts, clays and loose to medium dense sands underlain by saturated basal sands, gravel and cobbles up to 25m in thickness. Historical ground investigation information has thus far failed to provide confidence in the characterisation and engineering properties of this basal gravel and cobble layer due to limitations with conventional SPT, CPT and drilling techniques. The focus of this paper is primarily on characterisation of the basal sand and gravel units encountered in the River and North portions which largely drove the selection of innovative ground investigation techniques and methodologies.

A comprehensive ground investigation (GI) scope was proposed to support the bridge detailed design phase undertaken in parallel with the field works. This paper presents a perspective on the challenges of developing a ground model within this complex geological sequence and how this was addressed through a diverse, state-of-art GI campaign. It presents a methodology to derive ground profiles and soil parameters from advanced geotechnical testing and provides comparison of these innovative techniques against industry standard approaches.