ROCK BREAKAGE AND FRAGMENTATION

BAE has conducted unique and detailed investigations into rock breakage and fragmentation.

The purpose of the work was initially to better quantify the fragmentation that occurs during cave initiation and propagation, but the research has yielded some interesting results for the detailed analysis of seismicity, ground support and the homogenisation of material properties.

The work started with the construction of detailed, blocky rock masses using DFNs. These ‘synthetic’ specimens were then subjected to boundary displacements equivalent to typical laboratory tests to quantify the effects of specimen size and confinement and to ensure that the DFN models reproduced the material properties derived by calibration of global models using many thousands of field measurements.

After successfully demonstrating that the calibrated material behaviour was recreated by the explicit DFN models, the specimens were deformed using the complete displacement  histories for selected locations within a calibrated BAE global mine model. By repeating this last stage many times at different locations, the degree of primary fragmentation achieved at different locations within the cave column could be estimated. 

An extension of this work was the demonstration of an excellent correlation between total Dissipated Plastic Energy in BAEs calibrated models using the LR2 constitutive model, and the fragmentation estimated by the explicit DFN sub modelling procedure. Accurate only because the calibrated, LR2 global models accurately re-create the extent and magnitude of rock mass damage, the correlation allows an estimate of fragmentation in 3D, in almost any BAE mine scale model.

Figure: P80 (side length dimension of the 80th percentile fragment, by volume) on a section through a cave column. The figure is contoured to show the primary fragmentation  that was achieved during cave propagation.

An example of the results of this procedure is shown for the complex mine geometry in  the Figure above. The Figure shows the P80 (side length dimension of the 80th percentile fragment, by volume) on a section through a cave column. The figure is contoured to show the primary fragmentation  that was achieved during cave propagation.

This analysis is the first physics based simulation to produce  an estimate of fragmentation for the complete volume of a cave column and the surrounding rockmass. The techqnique has an immediate application for planned or current mine projects, and represents a step change in fragmentation forecasting and a significant opportunity for all caving mines.

The technique does demand the highest standards of model similitude and model set-up, but these are consistent with most recent BAE models for caving mines.

For more information, please contact David Beck in the BAE Mining Group.