Stability Analysis of Rib Pillars in Mechanized and Drill and Blast Excavations Using Numerical Modeling

Navid Bahrani, Fidelis T. Suorineni, Sean Maloney,
Abstract Stability of pillars is essential in achieving maximum safety and economic values in room-and-pillar and block cave mining projects. Today’s economic market is motivating underground mining companies to increase development advance rates and enhance their NPVs. There is a drive to move away from the conventional drill-and-blast as the main excavation method to alternative means such as mechanized excavation. The cyclic nature of drill and blast, and its inherent tendency to damage the surrounding excavation rock mass and increase support demand often result in poor advance rates. There is little experience with mechanized or non-explosive excavation methods in hard rock metalliferous underground mining. Therefore, the perceived benefits of mechanized excavation over drill-and-blast must be demonstrated. The application of numerical modeling in rock pillar stability analysis has recently become popular. In this paper a numerical modeling approach has been developed and used to investigate the impact of excavation method on the stability of hard rock rib pillars. Phase2, the two-dimensional finite element program was selected for the numerical analysis. The 3D advance of two parallel drifts in mechanized and drill and blast excavations is first modeled using the internal pressure reduction approach. The drill and blast excavation is simulated by assigning lower strength and stiffness properties to a zone adjacent to the excavation boundary representing a blast-induced damaged zone, while no such zone is considered to exist in the case of mechanized excavation. The mechanical properties of rock around the mechanized excavation, and the zone outside the perceived blast damage zone are kept the same, and higher than the blast damaged zone. The impact of excavation method on pillar stability is then assessed using the criteria including the distribution of stresses in the pillar, damage initiation and propagation thresholds, strainburst potential as well as depth of yielding.
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