Block caving methods rely on gravity to break and transport large amounts of ore and waste. Despite the importance of gravity flow, there is debate within the literature about the influence that the height of draw, particle size and particle size distribution has on the geometry of extraction and movement zones. This paper presents the results of an experimental programme conducted in the largest three-dimensional (3D) physical model to investigate the mechanisms of flow of cohesionless materials when drawing from a single drawpoint. Experimental results showed that isolated draw zones are mainly influenced by mass drawn and height of draw. Particle size was found to have a slight effect on extraction zones and no significant effect on movement zone width. Particle size composition (wide or narrow distributions) and drawpoint width were found not to have a major role on drawzone geometry. Those conclusions were based on statistical analysis of experimental data to define the controlling parameters in isolated draw. Model theory principles were used to investigate within the physical modelling framework the possibility of directly scaling the geometry of the extraction zones, which indicated that flow zones could be scaled in cohesionless materials under a set of assumptions. A mechanistic model of isolated draw is also postulated from experimental data from observations of stresses and the IMZ's geometry. r

Current production level design guidelines in block caving mines are based on the concept of interaction of movement zones and the spacing of draw-points at which mass flow is achieved. The limit of the isolated movement zone (IMZ) interaction has been determined by observations of the flow of sand and finely fragmented caved rock. This paper presents a study of the mechanisms and limit of IMZ interaction in coarse fragmented caved rock using a large 3D physical model. Results showed that when drawing from multiple drawpoints, the unmoved zone between IMZs is characterised by an increase in vertical load and a decrease in horizontal load. However, it was observed that the unmoved zones between the movement zones of adjacent draw-points did not enter the flow zone, despite drawpoints being spaced at less than 1.2 times the width of the IMZ. This result is in marked contrast to previous findings obtained in sand models, where movement zones have been observed to interact at draw-point spacings up to 1.5 times the width of the IMZ. The major reasons for the differences between the two different model results was found to be that significant stress arching and less induced vertical stress during flow was observed in the gravel model, in contrast to limited stress arching and more induced vertical stress in the sand models. It is hypothesised that significant stress arching would occur in block caving mines, and therefore that the results obtained in the gravel model maybe more representative of full-scale conditions. Movement zones in block caving mines may therefore not interact at draw-point spacings greater than the width of the isolated movement zone. r

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