Presented by Michael G. Jefferies on February 8th, 2024.
Finite element analyses using critical state theory proved necessary to understand the development of static liquefaction during three recent large tailings dam failures at Fundao, Cadia and Brumadinho. However, the complexity of these events prevents them being viewed as a complete
validation of the methodology - there are too many judgments over various aspects of each case history. Here we evaluate a far simpler case of static liquefaction: the 1974 Tar Island (Suncor, Alberta) slump, which involved a rapid drop of 5m during construction of a 12.5m high upstream raise over loose tailings. While not a dam stability issue, the event has the attraction of being load-induced, with simple geometry, and with known material properties and insitu state. The analyses were carried out with commercial software (PLAXIS) and use critical state theory with largely familiar soil properties measured by standard methods. The computed liquefaction develops from a prior drained condition, with essentially no precursors, before propagating rapidly undrained - there are similarities to the video record at Brumadinho and an animation will be shown to illustrate this. All aspects of the failure are replicated using properties as measured without "corrections", and in many ways this case history is a template for static liquefaction assessments. On a historical note, the theory and methodology were developed from construction in the Canadian arctic offshore 1982-9 by Gulf Canada Resources - this is very much a Canadian story, albeit one that is near fifty years old.
Permission to record was provided by the presenter.