Characterizing mine tailings for geotechnical design

Mine tailings are ground up rock and generally consist of sand and silt size particles, without clay minerals. Tailings “storage” (actually disposal) facilities are some of the largest constructed works, with seismic design an integral component. High value mines are frequently in earthquake prone areas and tailings liquefaction is an ever-present concern. A screening level liquefaction assessment based on the CPTu is a needed first step, but cannot be accurate because the fines content of tailings can be high, and engineering behaviour is only loosely related to fines content. An engineering mechanics based procedure is laid out in this paper which is applicable regardless of the fines content. It is anchored to the eighty year old principles of critical state soil mechanics originated by the Corp of Engineers. The state parameter provides the practical engineer an entry to this framework, as well as insight into a simple stability principle that sets the strategy for a tailings characterization project aimed at the analyses that a tailings engineer needs. The approach requires systematic in situ and laboratory testing to determine the soil mechanics properties of the tailings.