Raise caving is a novel mining method, which is based on the raise mining method. Raises are central and utilised for different purposes. Here only those directly related to the extraction of the orebody will be discussed. The main objective of raises is to utilise them for creating de-stressing slots, large drawbells and large stopes in an efficient manner. Remote-controlled or automated machinery is operated in raises. Further objectives of raises comprise monitoring and preconditioning. Depending on the field of application two different variants of raise caving can be distinguished, namely a de-stressing variant and a block caving variant.In the de-stressing variant, narrow slots are created first with the objective of providing stress shadows for mining activities in the subsequent production phase. Creating the slots in the de-stressing phase is high stress mining. Hence, massive pillars are left between slots to control the stress situation for de-stress raise development and mining-induced seismicity. After the de-stressing phase is completed, large-scale mineral extraction commences in de-stressed zones. In the production phase large drawbells are developed from raises and large stopes are extracted. During stope blasting only the swell of each blast is mucked so that blasted rock mass provides temporary support to the stope walls. After blasting is completed, the stope is drawn empty and the hanging wall is allowed to cave and caved hanging wall rock mass fills up the stope successively. The massive pillars are extracted in the course of large-scale stoping in the production phase too.In the block caving, variant raises are utilised for drawbell development, undercutting, preconditioning and monitoring purposes. Large drawbells are developed from raises. As drawbells are developed in upward direction, the roof area of the drawbells is enlarged constantly until continuous caving is initiated. Due to the integration of several key activities the block caving variant of raise caving is also referred to as integrated raise caving. This paper highlights the background and motivation for raise caving and it describes both raise caving variants. Steps for the implementation of the methods are outlined and advantages of the individual methods are outlined briefly. Key issues for the implementation of raise caving are highlighted and discussed, and an outlook on currently ongoing research and development activities, which include in situ tests of the method and machinery, is provided. Dedicated accompanying papers provide more information on the ongoing research and development.
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.
Cave mining progresses to depths exceeding 1000 m and ore bodies situated in competent and strong rock masses are nowadays extracted by different cave mining methods. Widely applied caving methods in massive deposits are block and panel caving, inclined caving, and sublevel caving. All caving methods have in common that rock mass caves during extraction of an ore body in a controlled way. As a result, regional stress changes occur, considerable abutment stresses form, and large-scale subsidence and significant seismic energy releases occur. Experience shows that these rock mechanics effects become especially critical at great depths, where primary stress magnitudes reach and exceed rock mass strength, as well as in strong competent rock masses, which require large footprints to enable continuous caving. The presented raise caving method addresses previously mentioned rock mechanics issues. Initially, de-stressing slots are developed from raises with a minimum amount of pre-development. Substantial pillars separate neighboring slots in order to control stress magnitudes and seismicity near slots. The slots provide a stress shadow for production infrastructure so that large-scale mineral extraction can take place in de-stressed ground. As mining progresses, pillars are extracted and hanging wall is allowed to cave. Results of a pre-study conducted together with LKAB have highlighted advantages of raise caving from a rock mechanics, safety, and cost point of view.
Pillar systems in mines are statically indeterminate systems. The paper presents the results of numerical investigations to evaluate the effects of panel dimensions on pillar loads. It is shown that pillar load in deep mines is strongly influenced by the lateral and vertical extent of extraction panels. The commonly applied tributary area concept does not account for these effects and is an oversimplification that has to be applied with caution. The effects of local pillar failures on stability of pillar workings are examined using simple models. It is shown that limiting panel dimensions by substantial barrier pillars can reduce the danger of regional pillar collapses and enhance overall mine stability.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.