Site characterisation along the Shipwreck Coast – two case studies using multiple geotechnical investigation techniques

Arup carried out geotechnical investigations at two sites along the cliffs of the ‘Shipwreck Coast’ in 2018. Proposed project works include a cantilevered steel box truss lookout at the existing 12 Apostles Castle Rock lookout (The Saddle Lookout), and a viewing platform spanning the cavern to the north-east of the Blowhole at Loch Ard Gorge (The Blowhole Lookout).

The geotechnical site investigations comprised borehole drilling and imaging, geophysics, and RPAS LiDAR and photogrammetry scans.

The sites are located in the Port Campbell Limestone region, with sub-vertical limestone cliffs up to 60m high. The cliffs are actively receding due to physical and chemical weathering. Erosion of the limestone cliffs has created the Blowhole at Loch Ard Gorge, and the steep cliffs and rock stacks at the Castle Rock Lookout and 12 Apostles area.

Careful characterisation of the structure and lithological units was required to input to a probabilistic assessment of future rockfall events impacting the proposed structures. This paper will present the methodology for characterisation, including site investigation and three dimensional modelling techniques. The paper will focus on how site investigation data was manipulated to inform the risk assessment and foundation design. A summary of the geological characterisation of the two sites is also presented.