• Title of Presentation

    Partial saturation influences on the CPT, strength and stability of silty tailings

  • Abstract

    Silty tailings inside a tailings storage facility may have a variety of saturated and unsaturated states. Large sections of tailings may have a mixture of air and water in the pores, and negative pore water pressure (or suction). This lecture gives an overview of how to deal with these properties when characterising the tailings using the CPT, and when assigning strengths that can be used in stability analyses. It is based on research conducted as part of a Future Fellowship and the TAILLIQ project (tailliq.com), each funded by the Australian Research Council, that latter also involving six mining companies.

     

    Laboratory-controlled CPT results for multiple silty tailings in a variety of saturated and unsaturated states, obtained using two calibration chambers, are presented then interpreted using a state parameter-based approach. For each tailings the cone penetration resistances are altered by the presence of air in the pores, and by suction’s enhancement of stiffness and strength, when the tailings are unsaturated. The cone penetration resistances can be normalised using the initial mean effective stress to establish relationships with the initial state parameter. It is shown how a relationship is unique for a given air content when defined as a fraction of the overall tailings volume. It is also shown how the relationships are bound by, and in some cases become equal to, those for saturated drained and undrained conditions. Application is demonstrated using CPT soundings in tailings storages from which the samples were taken, showing how in situ void ratio and state parameter, and a future state parameter if the tailings were to become saturated, can be determined. Close agreements with direct measurements of void ratios are shown.

     

    Also, the behaviour of unsaturated tailings, with high degrees of saturation, is presented, focussing on the propensity for static liquefaction during monotonic loading. Stress-strain behaviours are shown, relevant to a constant mass (closed-system) condition which may prevail during a fast-loading event. Practical implications are demonstrated by adding peak and post-liquefaction strength data, for unsaturated conditions, to charts which incorporate measures of initial state.

  • Biography

    Adrian Russell is a Professor in Geotechnical Engineering at UNSW Sydney. He is also an ARC Future Fellow and devotes 100% of his time to research on tailings liquefaction. His expertise is in laboratory element testing of soils and tailings, laboratory controlled CPTs and earthquake simulation, particle and pore geometry characterization, unsaturated soil mechanics and cavity expansion theory, and knowledge transfer to industry.

     

    He is an Australian representative on TC106 and TC221, which are International Technical Committees on unsaturated soil mechanics and tailings within the ISSMGE. He does expert review work on the stability of tailings storages and serves on Independent Tailings Review Boards. He is also on editorial boards of Geotechnique, Computers and Geotechnics and the International Journal of Rock Mechanics and Mining Sciences.

     

    He was awarded his PhD in 2005 and BE in 1998, each by UNSW Sydney. His first academic appointment was a lectureship at the University of Bristol in the UK (2003-2007). This was followed by a move UNSW Sydney where has been ever since.

     

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