In Adelaide, we frequently encounter a stark contrast between the stiff, fractured clays of the foothills and the alluvial soils of the plains. A simple borehole log rarely tells the full story when groundwater is a factor. The in-situ permeability test, particularly the Lugeon test for rock mass and the Lefranc test for soils, becomes the deciding factor in dewatering design. We have seen projects near the River Torrens where assumed permeability based on grain size alone was off by an order of magnitude. That is why we rely on direct field measurements to quantify how water actually moves through the formation, whether it is the fractured Adelaide Geosyncline bedrock or the Quaternary sediments. Complementing this with a CPT test often helps us identify the thin, high-permeability lenses that control the overall hydraulic regime.
A Lefranc or Lugeon test measures the formation's willingness to transmit water at a specific depth, data that no grain-size correlation can reliably predict in Adelaide's mixed geology.
