Shear wave velocity and small-strain stiffness across a broad range of states in iron ore tailings

Recent failures of iron ore tailings storage facilities highlight gaps in understanding the behaviour of these materials. Stiffness is an important tool in the assessment of static liquefaction triggering, and the monitoring of potential dam degradation that may result. This study evaluated the variation of the elastic stiffness across a wide range of void ratios and fines content, and proposes a new model for the variation of shear modulus with mean effective stress. As commonly found, the shear wave velocity is more stress dependent for tailings in a loose state than in a dense state, but compared to ‘natural’ soils, the shear modulus is significantly affected by the heavy (high specific gravity) fines content. These outcomes suggest that the addition of heavy fines (specific gravity > 3.5 vs ~2.7 of most natural soils) can increase the shear modulus without increasing the shear wave velocity. From these results, a boundary anchored to the state parameter that separates contractive and dilatative behaviour can be found using Vs measurements. This provides an important monitoring tool for iron-ore tailings dams in light of two recent failures (Fundão and Feijão) that displayed minimal prior warning.