Tonkin + Taylor, in collaboration with Tonkin + Taylor Group subsidiary Chadwick Geotechnics, played a pivotal role in completing the Coffs Harbour bypass project. The project is a 14 km four-lane bypass, serving as the final link in the Pacific Highway upgrade between Brisbane and Sydney.

The bypass diverts about 12,000 vehicles per day away from the town, saving up to 12 minutes of travel time by bypassing multiple sets of traffic lights. The project features three tunnels, three interchanges, and 26 bridges and cuts up to 40 metres deep, showcasing the scale and complexity of the undertaking.

Starting in October 2022 and completed in May 2023, our Tonkin + Taylor Australia and Chadwick Geotechnics teams had a dedicated team of 10 staff members on-site and in the office working on the northern section of the bypass. The project also benefits from the expertise and support of personnel from New Zealand, particularly in data interpretation.

A crucial aspect of the project involved extensive borehole drilling, totalling 1900 linear metres. The drilling included both non-core and HQ core drilling, with the deepest hole reaching 92 metres. Three rigs are deployed to accommodate the challenging terrain and limited access at many sites, and drilling is conducted over three weeks during night shifts under traffic control.

Our scope of work encompassed comprehensive testing and instrumentation. In-situ testing and instrumentation included:

  • Groundwater permeability “slug” tests
  • Packer permeability tests
  • Acoustic and optical televiewer inspections for downhole imagery
  • The installation of standard piezometers and multilevel VWPs for monitoring groundwater

Additionally, a wide range of soil laboratory testing was performed, including 1600-point loads and specialist rock testing.

To enhance data visualisation and navigation on-site, we used georeferenced maps created in QGIS and accessed through Avenza Maps. These tools allow for real-time information of location and sharing of tracks and facilitate efficient site navigation while providing easy access to existing borehole locations.


  • Borehole drilling
  • In-situ testing and instrumentation
  • Groundwater monitoring
  • 3D in-situ stress testing
  • Soil laboratory testing
  • Data visualisation and georeferenced mapping


  • 2022- present

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