Transitional Behaviour in Tailings

Failures of tailings structures have caused significant loss of life, even in recent years, most notably in China where 344 people were killed between 2001 and 2009. These failures have occurred under both static and seismic loading, liquefaction of the materials within the structure being a key hazard in both cases, often exacerbating an initial failure. In part these failures may reflect local lack of control of the design of such structures, but to some degree it must also indicate a lack of understanding of the mechanics of tailings materials, which are undoubtedly made more complex by the variety of materials that are disposed of in this way. There is an increasing amount of research on tailings, addressing their behaviour under monotonic and cyclic loading. In preliminary work carried out by the applicant, a number of tailings from different locations around the world were found to have transitional behaviour, with non-unique compression paths and non-unique critical state lines, so that the behaviour is strongly related to the initial density of the material when it was deposited or created. This mode of behaviour would make uncertain how existing methods of design within a critical or steady state framework, such as those based on a state parameter, might be applied. The project brings together both expertise and sources of tailings from several countries in which large numbers of such structures are built, with the aim of investigating when transitional behaviour might be expected in tailings and the implications for our understanding of their behaviour when it does.