Laboratory investigation on the transitional behaviour of tailings from a gold mine site in Australia

• Utilizes oedometer and triaxial tests on gold mine tailings from an Australian site to explore transitional behaviour. • Slurry deposition (SD) sample preparation better replicates the fabric and mechanical responses of intact specimens. • Demonstrates how different particle arrangements result from various preparation methods can lead to transitional behaviour. • Instead of a single critical state line (CSL), multiple CSLs are proposed due to transitional behaviour. Tailing dams constructed using the upstream method can be vulnerable structures, as they are partly founded on tailings deposits that are prone to liquefaction. Current stability and liquefaction analyses of tailings typically assume a single critical state line (CSL) in the volumetric plane. However, recent research has identified non-convergent compression paths and multiple CSLs in various soils, ranging from gap-graded soils to well-graded silts and sands, a phenomenon commonly termed transitional behaviour. An extensive analysis was conducted using oedometer and triaxial tests on tailings from an Australian gold mine site to investigate potential transitional behaviour. Tailings specimens with varying initial void ratios were reconstituted using moist tamping (MT) and slurry deposition (SD) methods and compared with intact specimens from the site. The findings underscored transitional behaviour in the tailings, characterized by non-convergent compression curves and multiple CSLs observed from different specimen preparation methods. Scanning Electron Microscopy-based fabric studies revealed variations in particle arrangement attributable to the preparation method, likely resulting the transitional behaviour. Furthermore, the study demonstrated that specimens deposited as slurries generally replicated the fabric and mechanical responses of intact specimens more accurately than those prepared using moist tamping. These findings emphasise the significance of transitional behaviour in tailings liquefaction analyses and advocate for reassessing the influence of fabric in laboratory specimen preparation for CSL determination.