Innovative applications of UAV-mounted remote sensing for the geotechnical assessment of Sturt River Dam

The assessment of the geological foundations of arch dams is required as part of the asset owner’s safety obligations (ANCOLD 2003). The task is often made difficult due to steep topography where arch dams are commonly constructed. Between 2013 and 2017, GHD was engaged by South Australia Water (SA Water) to examine the geological and geotechnical conditions of the Sturt River Flood Attenuation Dam (South Australia) abutment foundations. The dam was constructed between 1964 and 1966 within the Proterozoic “Sturt Tillite”. The foundations of the dam are characterised by a folded and fractured rock mass which creates complex spatial relationships between discontinuities and outcrop expression, difficult to assess in two-dimensional space. In collaboration with Monash University’s School of Earth, Atmosphere and Environment, a high resolution ortho-photogrammetric survey of the downstream dam abutments was undertaken using an Unmanned Aerial Vehicle (UAV) in areas where traditional mapping could only be obtained by rope access methods. Monash also undertook digital geological mapping of inferred discontinuities based on the UAV imagery. The data was then used to construct a three-dimensional (3D) model of the shape and position of high-persistence discontinuities, potentially critical to abutment stability. In addition to digital data, a low cost, high value field investigation to “ground-truth” the digital data and reviewed existing geological information (including rope access scanline data, foundation mapping and rotary cored boreholes) to develop a holistic understanding of the persistent discontinuities in their geological context.