Static Liquefaction of Mine Tailings - Fundamentals and Case Histories

Within the entire range of failure modes that have occurred at tailings impoundments static liquefaction is likely the most common, and at the same time likely the least understood. As design practice in many mining regions has in fact discounted the possibility of the mechanisms and criteria for this failure mode, the possibility of its occurrence has in fact often been overlooked in the search for other causes of failure. Static liquefaction, and the resulting flowslide of liquefied tailings materials, is shown to be a relatively common phenomenon among the more dramatic tailings impoundment failure case histories. Static liquefaction can be a result of slope instability issues alone, or can be triggered as a result of other mechanisms. The fundamentals of the liquefaction phenomena are summarized. Liquefaction is a term most often associated with seismic events. However, mine tailings impoundments have demonstrated more static liquefaction events than seismic induced events. The summary of the fundaments will include particular emphasis on static liquefaction. Several static liquefaction case histories are described to demonstrate various ways in which this failure mechanism has manifested itself. From an understanding of the fundamentals and the lessons learned from the case histories, basic guidelines to minimize the concern for tailings impoundments are presented.