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Calibration of Modified Cam-Clay Parameters for Red Mud Tailings : A Case Study

Tailings and Mine Waste Conference (2023 : Vancouver, B.C.); University of British Columbia. Norman B. Keevil Institute of Mining Engineering

Critical state soil mechanics proposes an integrated approach to soil behaviour, introducing the concept of critical state associated with the theory of hardening and softening plasticization. The critical state approach shows a more rigorous treatment in solving problems, especially those related to stress-strain behaviour. The dissemination of this concept is still relatively new in Brazil, especially among geotechnical engineers in the mining industry, where the limit equilibrium has been the main method to evaluate the factor of safety of the geotechnical structures for decades. This makes it necessary to develop studies that promote discussions about the benefits of the critical state approach. Therefore, this study presents the calibration of the Modified Cam-Clay parameters for red mud tailings and its evaluation by comparing the behaviour simulated by the model with i) the results of drained and undrained isotropically consolidated triaxial compression tests; and ii) the behaviour simulated by the widely used Mohr-Coulomb model. This study also shows an interpretation of the variation of the red mud behaviour with the variation of the degree of compaction of a trial dry stack assisted by the calibration of the Modified Cam-Clay model. The input parameters were defined after oedometer and triaxial compression tests, and GeoStudio© (SIGMA/W) was used for the numerical modeling. When compared to the triaxial compression tests, the Modified Cam-Clay model simulated the behaviour of the red mud tailings in drained and undrained conditions. The loose samples converged to an OCR lower than 2.5, and the dense samples to an OCR between 5 and 8, which showed that the dilatancy was simulated with the OCR variation. The calibration confirmed the limitations of the Mohr-Coulomb model in terms of stress-strain response. Unlike the Modified Cam-Clay, the MohrCoulomb model could not simulate adequately the strain rates and porewater pressure generation of the studied conditions. This highlights the importance of adopting the proper constitutive model in stress-strain studies. Finally, for the studied stress conditions, a strong dilative behaviour simulated by high OCR in the model was only identified for samples with an initial void ratio (prior consolidation) lower than 0.9 (degree of compaction of 104.5% of Standard Proctor). This suggests that the degree of compaction in the field could be adjusted to this value to minimize the deformations and the risk of failure of the structure.

Text

2023-12-08

Attribution-NonCommercialNoDerivatives 4.0 International

http://hdl.handle.net/2429/86785

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/