ANALYSES OF FLOW FAILURES OF MINE TAILINGS IMPOUNDMENTS

While earth dam engineering has evolved with the development of a large body of published theory and engineering practice, tailings embankment design and construction has received relatively little geotechnical engineering input until recently. Due to poor construction and maintenance practices, a considerable number of these impoundments have failed. A characteristic common to most tailings dam failures is that the mine tailings tend to liquefy and flow over substantial distances, with potential for extensive damage to property and life. The existence of these potentially hazardous earth structures is of considerable concern to the public and to the mining industries.; In order to be able to assess the potential for damage in case of such a failure, it is necessary to be able to predict the characteristics of the flow and the possible extent of flood movement. Developing suitable procedures for such analyses was the purpose of this research study.; The behavior of tailings materials during flow was represented for purposes of these analyses by the Bingham plastic rheological model, and a number of the well-known concepts of fluid mechanics were used in developing analysis procedures. Based on estimates of the values of Reynolds number, Hedstrom number, and Plasticity number it was expected that the flow of phosphate tailings would usually be turbulent, whereas flows of other types of tailings would usually be laminar. Therefore, different types of analyses are applicable to phosphate tailings on the one hand, and the remaining types of tailings on the other hand.; Currently available flood routing computer programs can be used without modification for analyses of potential inundation zones likely due to turbulent flows of phosphate tailings. Analysis procedures developed as part of this study can be used for analyses of flow failures of more highly viscous tailings which undergo laminar flow. These procedures are applicable for flow of tailings on horizontal and sloping planes and in prismatic valleys. The analyses can be performed using charts in the case of flow on planes, and a computer program "TFLOW" in the case of flow in prismatic valleys.; Flume experiments conducted as part of this study indicate that the analysis procedures developed are reliable. Application of these analysis procedures to field cases also showed reasonably good agreement between calculations and field observations. Thus the analysis procedures developed as part of this research study appear to provide a useful means for predicting the potential inundation regions downstream of mine tailings impoundments.