CPTu-Based Interpretation of Partially Drained Responses in Thickened and Conventional Mine Tailings

Abstract Cone penetration testing with pore-pressure measurements (CPTu) is used widely in tailings engineering, and most interpretation methods are formulated for fully drained or undrained responses. However, mine tailings often exhibit partially drained behavior, posing significant interpretive challenges because limited efforts have investigated this response. This study advances the understanding of partially drained responses in mine tailings by conducting variable penetration rate CPTu tests ( 0.2 – 15 cm / s ) in a tailings storage facility (TSF). Complementary field and laboratory tests, including shear-wave velocity measurements, vane shear tests (VSTs), and triaxial tests, supported the assessments. A salient aspect of the evaluated TSF is its use of both conventional and thickened tailings, enabling comparisons across different depositional methods. The study highlights key interpretation challenges, particularly the uncertainties in defining drained and undrained responses and the plausible range of backbone rate effect curves. Notably, conventional tailings exhibit greater variability due to their higher susceptibility to segregation and layering, leading to a broader range of partially drained responses than thickened tailings. A procedure that integrates numerical simulations and laboratory testing is presented to address the highlighted challenges and to constrain parameters of interest, such as the tailings’ state and the operative coefficient of consolidation. The procedure is illustrated using the collected data.