Slope design in brecciated carbonatite complexes under high-stress regimes

Carbonatites are generally competent rock masses with Rock Mass Rating class II rating 60-74. In spite of their competency, they tend to be affected by weak features like Mn-Fe veins and/or in situ rock damage due to brecciation associated with carbonatite complexes. Rock slope failure in such hard rocks is complex since such structures within the rock mass form weak links that could potentially control slope instability. In this contribution, a numerical simulation using phase(2) v 7.0 was carried out to investigate the influence of in situ rock damage on the stability of mine pit walls. The outcome reveals that the existence of breccia in the competent rock mass has the capability to reduce the slope stability performance particularly at gentle dipping angle of emplacement in close range to the slope toe. However, as the emplacement position of breccia moves away from the pit wall, the stability performance increases at gentle dipping angle < 50o. On the contrary, at the dipping angle of 50 degrees, the performance of slope reduced, and at steeper angle > 50 degrees, the impact becomes negligible. Thus, from a series of analyses, mine design in brecciated rock masses, the ratio of 1:5 between the breccia distance from slope toe and pit depth should be implemented to counter its impact. If the breccia is within or close to the pit limit, a deliberate effort must be made to mine out or truncate it.

Automated summary

Carbonatites are generally competent rock masses, but they can be affected by weak features and in situ rock damage. Rock slope failure in such rocks is complex due to the presence of weak links. Numerical simulation shows that the presence of breccia in the rock mass can reduce slope stability, especially at gentler dipping angles. However, as the emplacement position of breccia moves away from the pit wall, stability performance increases at gentle dipping angles. Therefore, mine design in brecciated rock masses should consider the ratio between the distance of breccia from slope toe and pit depth to mitigate its impact.