Physical modeling of high extraction columns in block cave mining

High extraction columns are one of the newest trends emerging in block cave mining. These columns present significant benefits in terms of preparation costs. However, they are also associated with significant challenges such as high stresses, the presence of fine material, risk of dilution, and the need to modify conventional mining designs. Given these challenges, understanding the behavior of the draw column during extraction is necessary to develop accurate mine designs and extraction plans in these environments. Then, for this study of gravity flow within high draw columns, experiments were conducted on a large 3D physical model scale model simulating isolated and uniform extraction in a high draw column (>600 m) composed of coarse and fine material. Two layouts, El Teniente and a Rectangular layout, were tested, the latter with spacings above the industry average. The results of isolated draw show that with fine granulometry the diameter of the Isolated Extraction Zone is 20 % smaller than that observed in the extraction column composed of coarse and fine granulometry. Additionally, it was found that both the geometry of the drawbell and the apex influence the Height of the Interaction Zone (HIZ) under uniform extraction. The El Teniente layout obtained an HIZ of 7.5 cm (15 m), while in the square layout, despite its large spacing, no stagnant material was observed above the crown pillar. Also as expected, the diameter of the flow zone is defined by the coarse fragmentation when the coarse material is below the fine fragmentation. Finally, based on the setup used here, the main contribution is that larger spacings do not produce a significant reduction in reserve recovery because the interaction height is related mainly to the extraction level pillar geometry and drawbell design.