Static liquefaction of Merriespruit gold tailings

Abstract

Static liquefaction is a concept that describes flow failures, such as those associated with tailings dams. This mechanism of failure is characterised by a sudden and dramatic loss in shear strength, followed by a flow of the liquified material over some distance. Static liquefaction may result from an increase in pore pressure due to a rise of the phreatic surface or an increase in the in situ shear stress due to an increase in tailings dam height, among various other processes. However, static liquefaction cannot be triggered unless the in situ material is inherently susceptible to a rapid collapse of the soil skeleton, characterised by a rapid and marked increase in pore pressure. The paper introduces the concept of static liquefaction and presents current research being carried out on static liquefaction, with particular emphasis to Merriespruit gold tailings. The paper provides detailed background on static liquefaction; the concepts, testing techniques, factors affecting and influencing test results and its importance and application to flow failures, liquefaction susceptibility and tailings dam safety. Current research being performed on Merriespruit gold tailings in terms of static liquefaction susceptibility is presented, including the effect of variation in grading on the steady state line. A brief introduction to the application and interpretation of static liquefaction susceptibility of actual tailings dams is presented. This is illustrated by applying liquefaction concepts to what is known about the in situ state of the Merriespruit tailings dam prior to its flow failure.