There are many inherent risks in creating a mine plan for a new ore zone in an underground mine; one of such risks is the redistribution of stresses that could be a cause for concern of instability. Numerical modelling has been increasingly used as a powerful tool for the assessment of mine plans from a geomechanics perspective. Using numerical modelling tools, it is possible to model the planned stope extraction sequence and evaluate the influence of mining induced stresses on the stability of remnant pillars, and use this information to remedy potential setbacks.
This paper demonstrates this approach through a case study of the short-term mine plan of the Lapa mine of Agnico-Eagle Mines Ltd., an underground gold mining operation located near Val d'Or, Quebec, Canada. Three-dimensional elasto-plastic modelling is used to compute mining-induced stresses and the extent of yielding in a remnant pillar, which is created by the stope extraction sequence as planned with a longitudinal retreat mining method
Numerical modelling has been increasingly used for a wide range of applications in civil, geotechnical and mining projects. Historically, the use of numerical modelling software required a high degree of expertise with using the software, and was only used to deal with very specific scenario, often requiring a lot of time to construct and analyze. With the increasing capabilities of computers and various utilities available on the market, engineers are able to incorporate the use of numerical modelling on a daily basis.
Numerical modelling software is now an invaluable tool for mine planners, who often require either a conceptual understanding of a scenario or a high-detail analysis. The application of such software has previously been used in many mine planning applications, such as dilution assessment [1], blast design [2] and sill pillar stability analysis [3].
This paper demonstrates an approach that can be adopted by mine planners to model a planned stope extraction sequence and analyze the influence of mining-induced stresses in remnant pillars. By adding a fourth dimension to numerical models (i.e. time), mine planners can effectively predict when significant stresses will develop in a remnant pillar, and take preventative measures such as destress slotting or destress blasting in high stress conditions, or pillar pre-drilling in the case of post-peak (yielding) conditions. This approach is exemplified through a case study of the short-term mine plan at the Lapa mine of Agnico-Eagle Mines Ltd., an underground gold mining operation outside of Val d’Or, Quebec.
The Lapa property is located at mid-distance (approximately 50 kilometres) between the cities of Vald’Or and Rouyn-Noranda, within the limits of the municipality of Rivière Héva, Cadillac Township. The Lapa property straddles the Cadillac-Larder Lake Fault Zone, a regionally extensive structure that is spatially related to numerous gold prospects and past producers. On the Lapa property, the Fault Zone is almost entirely taken up by the Archean-age Piché Volcanic Group (mafic to ultramafic schists).
