A comparison of procedures for determining the state parameter of silt-like tailings

After recent failures related to tailings storage facilities, the assessment of static liquefaction has become a major subject of interest in the mining industry. The standard procedures to evaluate global stability under liquefied conditions combines limit equilibrium with trigger analyses, which have fallen short -in some cases- in putting geotechnical risk off the table. Thus, deformation modelling incorporating high-end numerical procedures is often called in, requiring the calibration of a large number of material parameters that entails uncertainty and condition the robustness of the approach. One of the most challenging parameters to calibrate in tailings deposits is the state parameter for silt-like tailings that fall in the intermediate region between clays and sands. This work describes the application of the Shuttle & Jefferies (2016) methodology to estimate the state parameter along CPTu soundings using numerical cavity expansion element tests using Norsand, and a comparison with a more conventional approach like the one by Been & Jefferies (2016). The spatial distribution of the state parameter, when determined using this procedure and fed into a dam section, allows for defining regions of similar expected behaviour within the tailings body. An application for a tailings storage facility is illustrated, the results of two screening methods are compared and discussed.