Evaluation of undrained failure in foundation soil beneath tailings dam

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University of New Brunswick
Since the dawn of civilization, the majority of basic human needs have been obtained from mines. The rapid growth of population and the increase in need of mining activities accordingly have led to a rise in the amount of waste products (i.e. mine tailings). There have been 46 tailings dam failures around the world over the last two decades and this figure has been rising continuously. Among various reasons for tailings dam failure, the undrained failure in underlying fine-grained soils is considered to be one of the major contributing factors. In this study, an attempt was made to estimate the stability of a tailings dam in Elkview Operations (EVO) located approximately three kilometers east of Sparwood in the southeastern part of British Columbia. For this, a series of numerical analyses were performed using finite difference software (FLAC3D) to predict effective stress path in the underlying clayey silt layer, considering staged construction under undrained condition. The behavior of clayey silt layer under each construction stage was estimated by adopting the Modified Cam-Clay constitutive model. The factor of safety was then computed based on the critical state line and effective stress path. The analysis results showed that additional deposition of tailings can lead to a failure in the tailings dam, which can be initiated from zones below the toe of tailings dam. The sensitivity analysis results showed that the slopes of critical state and normal consolidation lines are the most influential parameters to the stability of tailings dam.