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A Review of the Bench Slope Design at the Aitik and Salmijärvi Open Pits, Sweden
R. Ortizm Golder Associates
P. Gómez, Itasca S.A.
The Aitik copper mine in Sweden is comprised of two open pits in competent host rock with a dominant, moderately-to-steep-dipping foliation. The scope of this work is twofold: first, a kinematic assessment of existing bench designs has been carried out based on a calibrated cumulative-frequency (CF) analysis. Secondly, a benchmark review compares the proposed designs with those of open pit mines in comparable conditions and which have had varied degrees of success from a stability standpoint. Taken together, the kinematic analysis and benchmark review aim to present the operator with a tool with which to critically review current bench designs from a geotechnical risk perspective and to provide a basis for future slope optimization.
The probabilistic kinematic analysis was carried out with a commercial probabilistic analysis tool developed by Itasca S.A. and is based on a well-established methodology. This approach considers the inherent variability present in the structural fabric to predict the occurrence of daylighting planar and wedge instabilities for a given slope orientation. Calibrated kinematic models were used to determine whether the designs comply with acceptance criteria and, such being the case, to identify potential for optimization.
The authors have also compared current designs with those of several operations with a similar geologic context: competent country rock, moderate to steep foliation/anisotropy and slope heights of more than 300 m. Different measures have been developed to compare hangingwall and footwall slopes, as each presents a unique set of challenges. Despite its simplicity, the benchmark review provides an idea of the aggressiveness of the design within the context of similar operations and their known bench performance.
Case E cutback 1 showing a transition from single to double benching.