53rd U.S. Rock Mechanics/Geomechanics Symposium,
New York City, New York
2019. American Rock Mechanics Association
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ABSTRACT: Many gold and base metals deposits in Western Australia are hosted in anisotropic rock masses. These may comprise bedded siltstones, sandstone and shales or foliated mafic and ultra-mafic rocks. When bedding or foliation are unfavorably oriented, slope instability mechanisms generally involve sliding along these anisotropy planes combined with joints or faults acting as release planes. When favorably oriented, instability mechanisms are typically complex step-path surfaces along various discontinuous joints, faults and bedding or foliation with breakages of intact rock bridges. Slope stability modelling techniques have evolved from basic kinematic analysis in the 1990s through to more complex two-dimensional limit equilibrium analysis and numerical modelling in the 2000s. Isotropic conditions were often assumed, although anisotropic models are became more widely used in the 2010s. Until recently, three-dimensional modelling was out-of-reach of most geotechnical engineers due to the model development and computing time required. This paper presents a case study from a large open pit mine in Western Australia that was assessed using 3D limit equilibrium and finite element methods and compares the results with 2D cross-sections.
Optimizing safe and economic slope designs is a critical part of many civil construction and mining projects. The chosen method of slope stability modelling, in many cases, has a significant impact on the final outcome.
As technology and computing capacity has improved over time, so has our ability to model and predict the behavior of rock slopes. For example, in the 1990's most rock slopes were modelled solely with stereographic projects using kinematic analysis to identify potential geological structures or structure sets that may induce sliding or toppling failures. Although still a very useful method today, there are many limitations to this approach, especially when dealing with larger slopes and in weak rock masses where complex failure mechanisms develop.
In the 2000's, limit equilibrium and finite element methods became popular with the use of 2D cross-sections for isotropic rock masses. Aside from the limitations associated with lateral curvature of most slopes and pits, many if not most rock masses are anisotropic. In the 2010's, directional shear strength models (or ubiquitous joint models) gained popularity to assist in modelling weaker shear strengths of anisotropy planes (e.g. bedding, foliations, pervasive joints, etc.).
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