A NUMERICAL INVESTIGATION OF STRESS PATH AND ROCK MASS DAMAGE IN OPEN PITS
The importance of establishing reliable slope designs becomes critical as the depth of open pits increases. Defining an optimum slope design that maximizes financial return and ore recovery without compromising safety conditions requires a proper evaluation of the stability conditions around the pit, and of the effects of instability on mining operations. Performing this analysis requires a good understanding of the behavior and strength of the rock mass at the slope scale. The use of simplified constitutive models, which overlook the effects of damage accumulation on the mechanical behavior of rock masses, adds to the degree of uncertainty of the results of stability analyses of large rock slopes. In this research, the relationship between damage and stress path is examined by using advanced numerical methods that allow the explicit representation of rock damage. The bonded particle method (BPM) has been used to evaluate the influence of stress path on damage accumulation, and on the strength of intact rock. The analysis of the influence of stress path on damage and strength at rock mass scale has been performed using the synthetic rock mass (SRM). From this analysis, it was possible to correlate the extension strain with the onset of yielding in the SRM sample. This limit was found to be independent of the confinement stress and the stress path followed to load the sample. A series of 3D numerical models were created to explore the correlation between in situ stress, stress path and rock mass damage. The relationship between the onset of yielding and extension strain from SRM modelling was used to define the areas in the pit models that might suffer relaxation induced damage. The extent of the zone where damage can develop has a direct relationship with the magnitude of the in situ horizontal stress. The geometry of the pit has an influence on the distribution of extensional strain around the pit, as the the increased confinement generated by slope curvature reduces the extent of the damage zone in the curved areas of the pit.
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