At present, a key hurdle for adopting such profiles is the presence of jointed rock masses exhibiting non-negligible anisotropic behaviour, which affect most open-pit mines. The proposal aims to solve this scientific issue and make optimal profiles possible for all open-pit mines. The resulting algorithms will be designed and implemented using software-based solutions relying on object-oriented programming languages such as C++ (Balsamo et al., 2017).
In the last 10 years, 4 independent systematic studies on the mechanical stability of slopes (Utili and Nova, 2007; Jeldes et al., 2015; Vahedifard et al., 2016) concluded that non-linear concave slope profiles are significantly more stable than the equivalent straight profiles. Recent work has led to a software, OptimalSlope (Utili, 2016), produced by OptimalSlope Ltd, the non-academic partner of the proposal, that systematically determines the optimal profile from a mechanical stability point of view for a given lithology, rock properties, and prescribed Factor of Safety (FoS). OptimalSlope seeks the solution of a mathematical optimisation problem where the overall steepness of the pitwall, from crest to toe, is maximised. Bench geometries (bench height, face inclination, minimum berm width) are imposed in the optimisation as constraints that bind the maximum local inclination of the sought optimal profile. The obtained optimal profiles are always steeper than their planar counterparts (i.e. the planar profiles exhibiting the same FoS, see Fig. 1a) up to 8° depending on rock type and severity of constraints on local inclinations. The optimal pitwall profile is defined as the overall steepest safe profile, i.e. OSA=OSAmax, with OSA being the inclination over the horizontal line joining the pitwall toe to the crest (see Figure 2).
So far, OptimalSlope has been adopted in three case studies of mines featured by isotropic rocks: a copper mine to be excavated in Chile (Utili et al., 2021), an existing North American gold mine to be enlarged (Agosti et al., 2021a), and the McLoughlin mine (Agosti et al., 2021b), a copper and gold mine whose data are available from a public repository. These works reveal that adopting optimal profiles realises reductions of the carbon footprint of up to 18.7% of the emission-related to mining activities. To provide some context, in the case of the McLaughlin mine, a reduction of 1.5 billion kg CO2 eq is realised. This is equivalent to the carbon sequestered by 24.6 million tree seedlings grown for 10 years and the greenhouse gas emissions avoided by 309 wind turbines producing electricity for a year, as calculated using Environmental Protection Agency (2021).