A framework for Interpreting Variable Penetration Rate CPTu Tests in Mine Tailings

Cone penetration testing with pore pressure measurements (CPTu) is widely used in tailings engineering, with most interpretation methods formulated for fully drained or undrained responses. However, mine tailings often exhibit partially drained behavior, posing significant interpretation challenges as 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 cm/s to 15 cm/s) in a tailings storage facility (TSF). Complementary field and laboratory tests — including shear wave velocity measurements, vane shear testing, and triaxial testing — further support 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. 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 framework that integrates numerical simulations of the CPTu penetration process 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 framework's application is showcased using the collected information.