Some comments on the prediction of mine waste beach slopes

The profiles of beaches formed by the hydraulic deposition of mine wastes from a pipeline are important in the design of mine waste impoundments. However, there is at present no satisfactory method of predicting the slopes of such beaches. In this paper, the compatibility with the available quantitative hydraulic data of the assumptions incorporated in existing models of deposition on mine waste beaches is explored. The available quantitative data show that flows on mine waste beaches may be laminar or turbulent and subcritical, but none support the occurrence of supercritical flows. Nevertheless the possibility that such flows occur cannot be discounted. The available data also show that deposition occurs in the main flow channels of both mine tailings and coal co-disposal beaches. Empirical correlations between the slopes of both mine tailings and co-disposal beaches and the dimensionless particle size of the wastes are presented. These may be used to obtain first estimates of such slopes, but have not been validated with independent data. Neither the range of particle sizes present in a given tailings nor the discharge appear to have a significant effect on the slopes of tailings beaches, but the slopes of thickened tailings beaches are strongly dependent on the solids concentration. Within normal operating limits, the slopes of coal co-disposal beaches appear to be largely independent of the solids concentration and particle shape