Critical state line of copper tailings under different loading types: mineralogy effect

Mining tailings can have mineralogy distinct from natural soils due to their anthropogenic nature. However, the effects of mineralogy on the critical state response of tailings have not yet been studied without the influence of grading. The reasons for differences in the critical state line (CSL) shape and position of geomaterials remain unclear, since the effects of gradation, mineralogy, loading type, particle size, shape and fabric are not well understood. Accordingly, this paper focuses on the effect of mineralogy on the CSL of copper tailings by evaluating two silty-sand tailings. Although these geomaterials exhibit similar gradations, they differ substantially in mineralogy. Triaxial compression tests under three degrees of compaction and four effective confining pressure values (ranging from 50 to 400 kPa) were performed and compared to published results under simple shear conditions. One copper tailings presented non-unique CSLs depending on the initial fabric and loading path, while the other exhibited unique CSLs regardless of the initial density or loading condition. The results also revealed the influence of mineralogy on the critical state parameter M, with the micaceous tailings presenting a lower critical state friction angle than the tectosilicate-rich one.