How does bench height selection directly impact slope stability and dilution control in open-pit mine design?

Bench height selection significantly impacts slope stability and dilution control in open-pit mine design. Bench height refers to the vertical distance between two consecutive levels in the pit. Slope stability is directly affected because higher benches contribute to higher overall slope heights. A higher overall slope increases the potential for large-scale slope failures, as the driving forces (gravity) are greater. This is because a taller slope contains more material, increasing the weight and therefore the forces acting to cause failure. Inter-ramp angles (the angle between the overall slope and the horizontal) are a critical parameter and influenced by bench heights, which must be appropriately designed with geotechnical assessment. Regarding dilution control, lower bench heights allow for more selective mining. Selective mining is the practice of extracting ore with greater precision, reducing the amount of waste rock included with the ore. Higher bench heights, in contrast, require larger equipment and less selective mining practices, leading to increased dilution. Dilution refers to the unwanted mixing of waste rock with the ore during the mining process, which lowers the overall grade of the mined material. For example, if a narrow, high-grade ore zone is mined using high benches, a significant amount of surrounding low-grade or waste rock will inevitably be included, diluting the overall grade and reducing profitability. Lower bench heights improve the operator's ability to follow ore boundaries closely. However, very low bench heights can increase mining costs due to the increased number of levels and the need for more frequent ramp relocations. Therefore, the selection of bench height is a compromise between slope stability, dilution control, mining selectivity, and overall mining costs. Detailed geotechnical investigations and careful mine planning are required to optimize bench height selection for a specific open-pit mine.