Tailings and Mine Waste Conference

Questa rock-pile weathering study : geotechnical characterization Van Zyl, Dirk


The Questa Weathering and Stability Study that was commissioned by Molycorp, Inc. (now Chevron Mining Inc., CMI) included extensive geotechnical characterization of the rock pile and analog materials. For the most part the Questa rock piles are matrix supported. This paper provides a summary of the geotechnical characterization results obtained during the research project. It provides summary level information and compares the summary statistics, especially the coefficients of variation, obtained for the results with those from previous studies as compiled in the literature. The results show that the variability as expressed by the coefficients of variation obtained for the Questa study is similar to those in the literature. These consistent results show that the geotechnical characteristics of the Questa materials do not contain significant “outliers”. Furthermore, the characteristics are consistent between rock piles so that all the data can be combined into one set of data for evaluation. It is expected that the friction angle will not reduce significantly with time as the rock piles age because geochemical evaluations concluded that new clay minerals will not form in the rock piles in the 100 to 1000 year timeframe. While weathering products may result in the deposition of cementation in the matrix it is not expected that this will result in measurable effects on the c-parameter. [All papers were considered for technical and language appropriateness by the organizing committee.]

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