Professor David Williams BE (Hons I), PhD, FIEAust, MAusIMM, CPEng, RPEQ

Director, Geotechnical Engineering Centre - University of Queensland

Keynote presentation: Some Geotechnical Fundamentals of Tailings Facility Design

Keynote summary: Tailings behaviour is very complex, even intractable.  When asked what he would do with liquefiable tailings, Dr Idriss said in 2018 "I'd avoid them." "You wouldn't build a water dam using liquefiable materials or sitting on a liquefiable foundation." "Why would we do it for tailings dams?" Dr Morgenstern has often said that if tailings are susceptible to liquefaction, assume they will (at some stage, which could be during operations or post-closure). The next question is what is their post-liquefaction strength? Fundao and Brumadinho both tell us that it’s in Pa as per its viscous flow, not 20% of the peak! We should separate tailings “containment” (aiming for a safe, stable and non-polluting landform in perpetuity, preferably built mainly from mine wastes, removing credible failure modes) from “storage” (with the motivation to maximise dewatering and density to minimise containment height and cost).  This is aligned with the GISTM. The Keynote will cover basic soil mechanics applied to tailings, address what is dense and dry enough not to liquefy, shear strength fundamentals including the critical state framework, and seepage.

Professor David Williams initiated and directs the Geotechnical Engineering Centre at The University of Queensland in Brisbane, Australia, and also manages the industry-funded Large Open Pit Project.  He has over 40 years of teaching, research and consulting experience.  He is internationally recognised for his expertise and experience in mine waste management and mine closure, in particular the design, construction, operation, closure and rehabilitation of tailings dams and waste rock dumps, including the design of covers, on which he has delivered a number of invited Keynote Lectures.  He was on the Expert Panel investigating the technical causes of the fatal Brumadinho tailings dam failure in Brazil in 2019 and serves on a number of Independent Technical Reviews Boards for Tailings Facilities in Australia and internationally.