Abstract
Traditionally the design of pitwall inclinations is carried out by geotechnical teams with little interaction with mining engineers. Usually the geotechnical engineer establishes the maximum inclination of any pitwall to be designed for the various geotechnical domains of the mine for a prescribed factor of safety chosen on the basis of the risk profile of the mine owner. Then, the mining engineer produces the strategic design of the mine determining pushback, pit shells and the ultimate pit limit by performing pit optimization (using L-G or the pseudo-flow algorithm) with the maximum acceptable pitwall inclination acting as a constraint. No further interaction occurs until the geotechnical team is asked to recheck the stability of the final pitwalls produced by the pit optimization software.
However, it is well known that the maximum inclination of a slope is a function not only of the prescribed factor of safety but of slope height as well. Imposing a pitwall maximum inclination irrespective of the pitshell target depth implies the current design methodologies give rise to suboptimal designs where often the pitwall inclination is either less of what could be (overly conservative) or more so that an inadequate factor of safety is adopted.
To overcome the current limitations, a methodology is here proposed where pitwall inclinations are selected accounting for the pit depth and integrated in the mining design. This is made possible by iterating (2 or 3 times typically) between pit optimizer and geotechnical pitwall design. The improvements in financial returns that can be gained by the adoption of the proposed methodology are showcased for two case studies of real gold and copper mines.