Abstract

Following the major tailings dam failures in Brazil, flow liquefaction is recognized as one of the major challenges for tailings dam design. There are thousands of existing centreline and upstream-constructed tailings dams around the world, both active and inactive, in which the risk of flow liquefaction needs to be assessed, and potential costly mitigation measures implemented.

A summary of recent developments in the evaluation of flow liquefaction for estimating both the in-situ state and the post-liquefied undrained shear strength of tailings is presented. Tailings are divided into clay-like and sand-like and the different approaches highlighted. The important role of material characteristics and high confining pressures for sand-like tailings are discussed. Soil compressibility reflected in the curvature of the Critical State Line is discussed and practical solutions presented. The parameter ψ/λ₁₀ is used to develop a unified relationship that integrates Critical State theory, laboratory test data and failure case histories to better estimate liquefied undrained strength ratio over a wide stress range. In-situ testing methods, in particular the cone penetration test, and issues such as partial drainage during the test are also discussed. The main concepts of Critical State are combined with case history observations to present practical solutions. Challenges regarding estimating trigger events will be presented with suggested solutions within a risk-informed approach.