ABSTRACT

  • Velocity based instability criteria for cave back instability, assessed by the DFE model allowing direct, explicit forecastin cave propagation geometry and rates.

  • Evolution of swell within the cave, computed by the NCA numerical method.

  • A physics based equilibrium state between the cave material and the uncaved rock mass computed by the DFE model.

  • Changes in load distribution within the cave and across the cave floor arising from the differential flow rates within the cave, consequent to the draw schedule.

  • Calibrated, energy based assessment of seismogenic potential.

  • Assessment of support performance via assessment of support demand versus capacity.

Coupled, granular flow-deformation simulations have been undertaken at a number of caving operations to simulate cave initiation, propagation and gravity flow. The tool combines a Newtonian Cellular Automata (NCA) representation of the cave muckpile with an explicit Discontinuum Finite Element (DFE) model of the rock mass mine scale and incorporate high resolution input data such as large numbers of explicit structures in the rock mass and very numbers of small particles in the cave muckpile. The coupled simulation incorporate :In this paper, example analysis results are compared to field measurements and interpreted in terms of the relation between modelled and measured draw, muckpile movements, cave growth and subsidence. The modelled stress, strain and energy changes in the rock mass are then used to describe aspects of cave initiation and propagation in terms of rock mass stability and seismicity.

1. INTRODUCTION

Problems with fragmentation, dilution, ore cut waste and propagation, leading to reduced recovery are common in modern caves. Some exam mechanisms of ore loss are shown in Figures 1, 2 and 3.

In the fictitious example shown in Figure 1, a slope failure induced by the effect of the cave on the pit slope results in mobilization of a volume of material on a scale not much smaller than the cave itself. The majority of the failure may be slow flowing, but compared to a similar cave with no overlying pit, there is a massive amount of additional waste that may dilute the cave a high risk that some of the waste will cut off displace flows of ore. If the failure contains a large volume of fines, the problem will be worsened and especially difficult to recover from. sometimes economically catastrophic.

The example shown in Figure 2 shows primary fragmentation for a conceptual cave, simulated using a DFE model. The model is a strain softening dilatant, Hoek Brown DFE model, calibrated with high fidelity forecast rock mass damage very well. The fragmentation estimate is based on the simulated plastic work and Bonds law. The model results for a section at the edge of the cave shows how structures concentrate and partition strain, leading to compartments of favorable and poor fragmentation.

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