Authors: Koch, LA; Ladinig, T; Wimmer, M; Wagner, H; Grynienko, M

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Koch, LA, Ladinig, T, Wimmer, M, Wagner, H & Grynienko, M 2022, 'Key issues related to oreflow in raise caving', in Y Potvin (ed.), Caving 2022: Proceedings of the Fifth International Conference on Block and Sublevel Caving, Australian Centre for Geomechanics, Perth, pp. 1397-1410,

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Oreflow was identified as a key issue for the successful implementation of the novel raise caving (RC) method. Critical excavations for the method are narrow de-stress slots and large production stopes. During extraction, slots and stopes are filled with blasted ore, which supports the excavation walls. To extract the ore, it needs to flow properly towards the drawpoints. Otherwise, voids can form, which serve as space for the hangingwall to cave into and cause dilution. Another critical aspect of oreflow is the avoidance of hang-ups in narrow slots. These can interfere with the predefined draw strategy, can form stress bridges which weaken the de-stress effect and are difficult to remove, especially in higher regions of the slot. Additionally, an even lowering of the bulk material should be achieved to form a free surface on top of the slot and stope. The surface is important to allow a subsequent blast conducted from raises above, which are an essential part of the infrastructure. For a beneficial environment of oreflow, a well-planned mine design and draw strategy are essential. The emphasis in this paper is to highlight the key issues related to oreflow. The key issues, namely avoiding dilution, avoiding hang-ups and the creation of a free surface are individually defined, outlined and described. For this purpose, the oreflow in the large drawbells, which are utilised in raise caving, is analysed further with numerical simulations. The drawbell design is intended to be approached on two sublevels which is beneficial for a complete covering of the stope. Further, such a drawbell design may show positive effects on stability due to a lower amount of infrastructure on each level. The simulations are done by means of the discrete element method (DEM). One part of the work considers the influence of drawbell shapes on the oreflow. It shows that an inclination for the large drawbell of around 60° is advantageous to enlarge the extraction zone. Additionally, the spacing of drawpoints is varied to investigate the effect of proper spacing on the overall flow situation. Thereby, a positive influence of the large drawbell on the interaction between the drawpoints could be shown. The results of the models and outcomes are presented in this paper to highlight the advantages of large drawbells for oreflow.

Keywords: oreflow, raise caving, mine design, discrete element method simulation, drawpoint spacing, drawbell inclination

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