Session
Numerical Modelling I, Finger Rock Room
Abstract Summary
Open pit slope design in the bedded units of Australia’s Pilbara iron ore mines is challenging in many aspects. Data collection and interpretation, slope stability assessment, and implementation of design parameters in these anisotropic rock masses requires experience and specialized expertise, as there are numerous complex considerations. The selection of an appropriate strength model for each stability analysis depends on the rock units present and the anisotropy orientation.
2D limit equilibrium methods, incorporating the Snowden modified anisotropic linear model, are commonly used for stability assessments in these anisotropic rock masses. The outcomes using this method are sensitive to analysis methods, slip surface search limits and methods, and key model inputs. It is important that the potential failure mechanisms are well understood and suitably analysed. A critical part of the slope design process is the identification of design domains and the selection of representative sections for stability analyses. In these analyses, the slope stability is considered to be controlled either largely by bedding or entirely by the rock mass strength, though in fact neither assumption may adequately represent reality. 3D analyses may need to be adopted for advanced levels of study to better capture failure mechanisms in the context of rock mass confinement and bedding obliqueness relative to pit slopes.
This paper presents the results of finite difference 3D analyses to demonstrate the impact of bedding obliqueness on slope stability and the advantages of 3D analyses in optimising pit slope angles. These analyses have allowed for better understanding and prediction of the stability controls, so that these can be considered where only 2D analyses are able to be carried out. The analyses demonstrate where the results of 2D analyses of isotropic conditions are conservative, presenting opportunities for slope steepening; and conversely where 2D analysis may significantly overestimate the stability of a slope design, presenting increased risk of failure.
Authors
- Jayanthan Mylvaganam | SRK Australia
- Ian de Bruyn | SRK Australia
- Justine Paul | BHP
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