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Seal Rocks Road Slip


An Aquares geophysical survey was undertaken for Great Lakes Council to assess the cause of a major road slip near Seal Rocks (Figure 1). The root cause of the slip was unknown and the nature of the terrain meant the repair would be costly so it was important to get it right.

Figure 1: Aquares for land was utilised to investigate the root cause of a road slip in Seal Rocks, NSW.

An Aquares for land survey was undertaken on both sides of the road and a ground model produced (Figure 2). The ground model highlighted a thin (30cm) saturated clay layer between the road base and the rock and this was later confirmed in boreholes. Due to the very thin and subtle nature of the clay layer it most likely would have been missed during the course of a normal borehole study. However, because the layer was identified during the geophysical study, it was successfully targeted and sampled by the drillers.

Any subsequent fix of the road would likely require pinning through the road base and well into the rock to prevent further slips. If only drilling had been done and the clay layer wasn’t detected then a less suitable repair method may have been adopted. This could have led to further road failures in the future. The ground model also highlighted risks either side of the slip that need to be addressed.

Figure 2: A thin, highly saturated clay layer is seen in the cross section of the slip region. Findings were later confirmed utilising boreholes and the clay layer was detected as the geologist was looking for the layer.

Sustainability Outcomes

  • Environmental benefits: Assist with preventing further slips. Reduced resource and energy use required for rework.
  • Economic benefits: Cost savings as adequate repair of the road able to be conducted properly and repeat work unlikely to be required.
  • Social: Improve safety in the area of the slip due to good understanding of the causes of the failure and ability to put appropriate prevention measures in place.

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