Interpretation of state parameter in partially drained tailings: A case history examination

Estimating state parameter in tailings storage facilities (TSFs) is a key component to assessing their stability. The cone penetrometer test (CPT) forms the key tool to all current methods to enable rapid assessment of in situ state parameter. Methods to estimate state parameter from the CPT in common use range from screening-level techniques to drained and undrained cavity expansion methods. Importantly, there is no comprehensive method, such as a cavity expansion-based approach, for partially drained CPT soundings. This paper outlines further investigation of a recent study where state parameter had been estimated using screening methods and through direct comparison of in situ void ratio (through water content) to the critical state line measured on reconstituted samples. In the current study, the state parameter was estimated on the basis of both drained and undrained cavity expansion solutions. This was done as although the sounding in question was partially drained, the drained and undrained cavity expansion solutions represent accepted leading practice in TSF investigations. The results of this comparison indicate that the use of drained and undrained cavity expansion tools appears to over- and under-estimate state parameter, respectively. Implications for tailings engineering practice, and ways forward for this issue, are discussed.