Applying the Engineering Geological Model Approach to Quaternary Glacial Geology in Western Tasmania

Tasmania is unique in Australia for its extensive, preserved glacial landscapes, which are concentrated in remote areas. Numerous high-value mining and hydroelectric assets in those settings necessitate understanding of glacial features, including their geomorphological indicators, stratigraphical complexity, and geomechanical conditions. At least five Quaternary glaciations of progressively more limited extent have been differentiated in Tasmania. They span from at least the Early Pleistocene (ca. 1 Ma) to the Last Glacial Maximum (ca. 20-18 ka) with all glaciers having disappeared by 14 ka. Glacial deposits can be geotechnically challenging due to high heterogeneity and anisotropy, producing complex lateral and vertical variations in geomechanical properties. The wide age range of Tasmania’s glacial deposits contributes further complexity through variations in weathering and cementation. The Engineering Geological Model (EGM) approach helps firstly to effectively identify and assess geological relationships and geotechnical properties, and secondly to adequately address these conditions during engineering design and construction. In previously glaciated landscapes, this approach provides an important framework to enable thorough understanding of complex deposits, consequent geomechanical behaviour, and potential hazards. This paper outlines the geotechnical investigation methodologies that are potentially suitable for diverse glacial units and demonstrates the utility of the EGM approach through its application to a new tailings storage facility at Renison Bell in western Tasmania. There, three glacial units were encountered: surficial, glaciofluvial sandy gravel of variable thickness and permeability; weak, liquefiable, rhythmically laminated glaciolacustrine silt and clay; and previously unidentified, locally indurated till draping bedrock. Their properties, stratigraphical relationships, and geographical distributions suggest that these units record the first two glaciations to affect Pieman Valley. A desktop study and conceptual model, substantially refined as an observational model, provided interpretation confidence and enabled completion of construction on time.