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During the underground excavation of highly valuable material, many mines will adopt structures, such as shafts, to outflow the material mined by surface methods and reduce the haulage distance. Such shafts, which are typically vertical, have crushing facilities that can be applied to surface mining processes until the crushed material is ready for transportation. The use of shafts for this purpose has been associated with the elimination of stretches of roads that exist between the pit limits and mineral processing facilities and/or waste piles.
While this type of method is useful for ore bodies with strongly inclined slopes, it is limited for other types of mining operations, such as open-pit mining. Furthermore, these strategies are also sustainability limited, as these methods are often insufficient in reducing greenhouse gas emissions (GHG) unless productivity, mine scheduling and, waste management procedures are compromised.
Sustainable Mining and Trucks
Despite the numerous active sustainable mining operations that exist around the world, the mining industry remains largely dependent on trucks. The mining industry is therefore inevitably associated with high GHG emissions and increased fossil fuel consumption, as well as excessive mineral dust, noise and vibration generation by blasting operations.
To reduce this dependence, several mining projects have emerged. For example, research has shown that replacing trucks with more efficient mining equipment can significantly reduce carbon dioxide (CO2) emissions and the overall cost of mining operations. Carry dozers as an alternative have been shown to significantly improve fuel consumption and productivity rates when applied to short-distance haulage procedures.
A Novel Methodology to Sustainable Mining
Brazilian researchers investigated the potential of an innovative mining method that combines underground mining structures with surface mining operations, with the hope that the truck fleet, strip ratio and overall environmental impact of the mine would drastically change. This was developed in four steps that included an initial assessment of the underground structures that were used to transport materials between the mining faces and their processing facilities. Once assessed, the researchers designed the open-pit mine and obtained mine scheduling of the operational variables, economical parameters, and application of underground structures. Both the pit and mine design was then optimized before the completion of a pit report that compared traditional scenarios with those proposed by the authors.
Creating Underground Routes
One of the key components of this study was replacing trucks and haul road structures with underground routes, which required a path to be created between the mining faces and their mineral processing facilities. The design of this underground route proposed the use of shafts, where dozers will be used to drive the haulage of all ore cuts and waste rocks. Before any material that has been cut by the bulldozers can pass through the shaft, the researchers placed galleries below the ultimate pit surface. The precise placement of these galleries ensured that all mined material in the project could smoothly move through the openings, while also preventing the passage of excessively large blocks.
Whilst the researchers were planning their underground mining routes, several key factors were considered, including the mechanical strength features of the mass of the rocks, and the determination of how the mass strains support. Additionally, researchers needed to calculate the effective resistance stresses that could act on all underground structures to fully establish excavation stability during mining operations.
Like all other underground mining routes, the structures designed by this group were complex and therefore proved to be difficult for the engineers to achieve. In addition to these inherent difficulties, the researchers were also limited in their ability to accurately predict the geological structure configuration and geomechanical conditions that would arise each day.
The underground route designed by the researchers of the current study was found to achieve an 8.3% strip ratio reduction, demonstrating that their proposed methodology successfully created a more sustainable mining strategy by lowering space requirements. Further applications of the feasible design proposed by this study will hopefully improve the sustainability of larger mining enterprises, while simultaneously eliminating the need for mines to constantly depend on road infrastructure, trucks and shovels to perform daily tasks. As these factors continue to lessen, it is predicted that the overall fuel consumption requirements of the mining industry will subsequently follow.
- Rodovalho, E., Passos, A. O., de Tomi, G., & Tenorio, J. A. S. (2019). Sequential glory hole approach as a new mining method for sustainable operations. Journal of Materials Research and Technology 8(5); 4788-4796. DOI: 10.1016/j.jmrt.2019.08.025.