Static and Cyclic Liquefaction of Copper Mine Tailings

Abstract

Motivated by recent failures of tailings storage facilities (TSFs) around the globe, the tailings community is actively working to better understand the mechanical behavior of mine tailings. This study presents a geotechnical characterization (at both the laboratory and field scales) of copper mine tailings from a TSF located in an area with high seismicity, which makes assessing their response to static loading (e.g., static liquefaction) and earthquake-induced demands (e.g., cyclic-induced liquefaction) of primary importance. We discuss relevant aspects in the behavior of the examined mine tailings, including compressibility, stiffness, and the liquefaction (static and cyclic) response. Salient findings include the following: (1) the void index concept appears to characterize the compressibility of mine tailings regardless of ore source; (2) the stiffness-confinement dependence for the examined tailings contrasts with typical sand models; (3) theoretical particle size distributions that promote packing are useful for understanding trends in the location of the critical state line; (4) the examined tailings can experience static and cyclic liquefaction regardless of fine contents (insights on the observed responses are shared); (5) commonly used strain-based criteria are not robust enough to identify the cyclic liquefaction onset, thus we propose different criteria based on mechanistic descriptors; (6) the cyclic response of the examined tailings is affected by coupled stress-compressibility effects and their postliquefaction response fit within the expected response of natural silty soils; and (7) our assessment of state-of-practice liquefaction triggering procedures, in the context of the recently proposed ΔQ method, suggests a comparable performance for the tailings examined in this study. In addition, a soil behavior index (IC) of 2.9 is consistent with the ΔQ=20 as suggested in the literature for assessing liquefaction susceptibility of the examined tailings.